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RFC 0841

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Specification for message format for Computer Based Message Systems

Part 1 of 4, p. 1 to 34
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Obsoletes:    0806


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      RFC 841
	
      FIPS Pub 98


      SPECIFICATION FOR MESSAGE FORMAT FOR COMPUTER
      BASED MESSAGE SYSTEMS
	

      27 January 1983


      National Bureau of Standards


      This RFC is FIPS 98.  The purpose of distributing this document
      as an RFC is to make it easily accesible to the ARPA research
      community.  This RFC does not specify a standard for the ARPA
      Internet.

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                              TABLE OF CONTENTS




                                                                   Page



      EXECUTIVE SUMMARY                                               5



      1.  INTRODUCTION                                                7


          1.1  Guide to Reading This Document                         7
          1.2  Vendor-Defined Extensions to the Specification         8
          1.3  The Scope of the Message Format Specification          8
          1.4  Issues Not Within the Scope of the Message Format      8
               Specification
          1.5  Relationship to Other Efforts                          9



      2.  A SIMPLE MODEL OF A CBMS ENVIRONMENT                       10


          2.1  Logical Model of a CBMS                               12
          2.2  Relationship to the ISO Reference Model for Open      14
               Systems Interconnection
          2.3  Messages and Fields                                   14
          2.4  Message Originators and Recipients                    15



      3.  SEMANTICS                                                  17


          3.1  Semantics of Message Fields                           17
               3.1.1  Types of fields                                17
               3.1.2  Semantic Compliance Categories                 18
               3.1.3  Originator fields                              18
               3.1.4  Recipient fields                               19
               3.1.5  Date fields                                    20
               3.1.6  Cross-reference fields                         21
               3.1.7  Message-handling fields                        22
               3.1.8  Message-content fields                         23
               3.1.9  Extensions                                     23

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          3.2  Message Processing Functions                          24
               3.2.1  Message creation and posting                   24
               3.2.2  Message reissuing and forwarding               25
                    3.2.2.1  Redistribution                          26
                    3.2.2.2  Assignment                              28
               3.2.3  Reply generation                               28
               3.2.4  Cross-referencing                              29
                    3.2.4.1  Unique identifiers                      29
                    3.2.4.2  Serial numbering                        30
               3.2.5  Life span functions                            30
               3.2.6  Requests for recipient processing              31
                    3.2.6.1  Message circulation                     31
          3.3  Multiple Occurrences and Ordering of Fields           31



      4.  SYNTAX                                                     34


          4.1  Introduction                                          34
               4.1.1  Message structure                              34
               4.1.2  Data elements                                  35
                    4.1.2.1  Primitive data elements                 36
                    4.1.2.2  Constructor data elements               36
               4.1.3  Properties                                     36
                    4.1.3.1  Printing-names                          37
                    4.1.3.2  Comments                                37
               4.1.4  Data compression and encryption                37
          4.2  Overview of Syntax Encoding                           37
               4.2.1  Identifier Octets                              38
               4.2.2  Length code and Qualifier components           39
                    4.2.2.1  Length Codes                            41
                    4.2.2.2  Qualifier                               42
               4.2.3  Property-List                                  44
               4.2.4  Data Element Contents                          44
          4.3  Data Element Syntax                                   44
               4.3.1  Data elements                                  45
                    4.3.1.1  Primitives                              47
                    4.3.1.2  Constructors                            49
                    4.3.1.3  Data Elements that Extend this Speci-   52
                             fication
               4.3.2  Using data elements within message fields      53
               4.3.3  Properties and associated elements             54
               4.3.4  Encryption identifiers                         54
               4.3.5  Compression identifiers                        54
               4.3.6  Message types                                  55

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      SUMMARY OF APPENDIXES                                          56



      APPENDIX A.  FIELDS -- IMPLEMENTORS' MASTER REFERENCE          57



      APPENDIX B.  DATA ELEMENTS -- IMPLEMENTORS' MASTER REFERENCE   63



      APPENDIX C.  DATA ELEMENT IDENTIFIER OCTETS                    71



      APPENDIX D.  SUMMARY OF MESSAGE FIELDS BY COMPLIANCE CATE-     72
                   GORY


          D.1  REQUIRED Fields                                       72
          D.2  BASIC Fields                                          72
          D.3  OPTIONAL Fields                                       72



      APPENDIX E.  SUMMARY OF MESSAGE SEMANTICS BY FUNCTION          74


          E.1  Circulation                                           74
          E.2  Cross-Referencing                                     74
          E.3  Life Spans                                            74
          E.4  Delivery System                                       74
          E.5  Miscellaneous Fields Used Generally                   75
          E.6  Reply Generation                                      75
          E.7  Reissuing                                             75
          E.8  Sending (Normal Transmission)                         75



      APPENDIX F.  SUMMARY OF DATA ELEMENT SYNTAX                    76



      APPENDIX G.  SUMMARY OF DATA ELEMENTS BY COMPLIANCE CATEGORY   78


          G.1  BASIC Data Elements                                   78
          G.2  OPTIONAL Data Elements                                78

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      APPENDIX H.  EXAMPLES                                          80


          H.1  Primitive Data Elements                               80
          H.2  Constructor Data Elements                             82
          H.3  Data Elements that Extend this Specification          87
          H.4  Fields                                                88
          H.5  Messages                                              90
          H.6  Unknown Lengths                                       94
          H.7  Message Encoding Using Vendor-Defined Fields          97
               H.7.1  Example of a JANAP-128 Message                 97
               H.7.2  Encoding of Example using the FIPS Message     97
                      Format
               H.7.3  Field Mappings of JANAP-128 to FIPS Format    101
               H.7.4  Vendor-Defined Fields                         101



      REFERENCES                                                    103



      INDEX                                                         105

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                               LIST OF FIGURES




      FIG. 1.    LOGICAL MODEL OF A COMPUTER-BASED MESSAGE SYSTEM    12
      FIG. 2.    MESSAGE FORWARDING AND REDISTRIBUTION               27
      FIG. 3.    EXAMPLE OF MESSAGE CIRCULATION                      32
      FIG. 4.    STRUCTURE OF IDENTIFIER OCTETS                      39
      FIG. 5.    ENCODING MECHANISM FOR QUALIFIERS AND LENGTH        40
                 CODES
      FIG. 6.    REPRESENTATION OF LENGTH CODES                      42
      FIG. 7.    EXAMPLES OF QUALIFIER VALUES                        43

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                               LIST OF TABLES




      TABLE 1.    FIELDS USED IN MESSAGE PROCESSING FUNCTIONS        24
      TABLE 2.    HIGH-ORDER BITS IN THE IDENTIFIER OCTET            39

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                             Federal Information
                     Processing Standards Publication 98
                               27 January 1983
                         Announcing the Standard for


                               MESSAGE FORMAT
                                     FOR
                       COMPUTER BASED MESSAGE SYSTEMS



      Federal  Information Processing Standards Publications are issued
      by the National Bureau of Standards pursuant to section 111(f)(2)
      of the Federal Property and Administrative Services Act of  1949,
      as  amended,  Public  Law 89-306 (79 Stat. 1127), Executive Order
      11717 (38 FR 12315, dated May 11, 1973), and Part 6 of  Title  15
      Code of Federal Regulations (CFR).

      Name  of  Standard.  Message  Format  for  Computer Based Message
      Systems (FIPS PUB 98).

      Category of Standard. Software Standard; Interchange Codes, Media
      and Data Files.

      Explanation.  This  standard  separates  information  so  that  a
      Computer  Based  Message  System  can  locate and operate on that
      information (which is found in the fields of messages).  This  is
      the  first of a family of standards which will ensure information
      interchange among Computer Based Message Systems.

      Approving Authority. Secretary of Commerce

      Maintenance Agency. Department of Commerce,  National  Bureau  of
      Standards (Institute for Computer Sciences and Technology).

      Cross Index. Not Applicable.

      Related Documents.


         a. American   National   Standard   Code  for  Information
            Interchange (ASCII), X3.4-1977,FIPS PUBS 1-1.

         b. American National Standard  Code  Extension  Techniques
            for  Use with the 7-bit Coded Character Set of American
            National  Standard   Code   (ASCII)   for   Information
            Interchange, X3.41-1974, FIPS PUB 35.

         c. National  Bureau  of Standards.  Calendar Date. Federal
            Information Processing Standards  Publication  4,  U.S.

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            Department  of Commerce / National Bureau of Standards,
            November, 1968.

         d. National Bureau of Standards. Data Encryption Standard.
            Federal Information  Processing  Standards  Publication
            46,  U.S.  Department  of  Commerce/National  Bureau of
            Standards, January, 1977.

         e. National Bureau of Standards. Representation  of  Local
            Time  of  the  Day for Information Interchange. Federal
            Information Processing Standards Publication  58,  U.S.
            Department  of Commerce / National Bureau of Standards,
            February 1979.

         f. National  Bureau  of   Standards.   Representation   of
            Universal  Time,  Local  Time Differentials, and United
            States   Time   Zone   References    for    Information
            Interchange.  Federal  Information Processing Standards
            Publication 59, U.S. Department of Commerce /  National
            Bureau of Standards, February, 1979.


      Applicability.  This  message  format standard applies to Federal
      departments  and  agencies  in  their  acquisition  and  use   of
      computer-based  message  systems (CBMS) and services in networked
      systems,   except   for   certain    single-processor    systems.
      Specifically,  the  standard  does not apply to a CBMS if it is a
      stand-alone system which is not  interconnected  with  any  other
      CBMS:  nevertheless, conformance with the standard is recommended
      under these circumstances particularly if there is a  possibility
      that  use  of another central processing unit, or interconnection
      with another system, will be required in the future.  Where a new
      CBMS node is incorporated into an existing network, the  standard
      applies  at  the  interface  between  CBMS's.  In  this instance,
      previously existing nodes may  accommodate  the  standard  either
      through  retrofit  or  by  the use of a translator.  In addition,
      networks  that  are  established  strictly  for  the  purpose  of
      supporting  research  in  computer  science or communications are
      exempt from complying with this standard.

      Subcommittee TC97/SC16  of  the  International  Organization  for
      Standardization   (ISO)  has  developed  a  reference  model  for
      describing communications between "open" systems.  (ISO/TC97/SC16
      DIS7498) This model is known as the ISO Reference Model for  Open
      Systems   Interconnection   (OSI).    It  divides  communications
      protocols   into   seven   layers,    ranging    from    physical
      interconnection   at   the  lowest  layer  to  data  exchange  by
      applications programs at the top.

      The NBS message format deals with data  used  by  an  application
      within  a  system; it is not a protocol.  Messages defined by the

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      NBS   message   format   would   be  manipulated  by  a  layer  7
      (Application) protocol.

      A message as referenced by the NBS message format is  a  unit  of
      communication from an originator to a recipient, exclusive of any
      message  heading  or  control information (often referred to as a
      message envelope).  An originator  and  recipient  are  typically
      people  but  may  be  roles  or  processes.   A role identifies a
      function within an organization as opposed to an  individual  who
      performs  that  function.  A process refers to a computer process
      that might originate or receive a message.

      Special Information. Certain characteristics distinguish  a  CBMS
      from  other  systems  for  sending  messages.    Originators  and
      recipients  may  be  terminal  users   or   processes   (discrete
      software).    A  system  in  which  the  originator  addresses  a
      particular terminal device rather than a particular recipient  is
      not  considered to be a CBMS.  The recipient's system need not be
      available when the originator sends a message.  The  message  can
      be  stored  in the originator's system or at an intermediate node
      in the network until the recipient's  system  becomes  available.
      In  addition,  a  CBMS  offers  both message creation and message
      processing facilities as part of the system.  A CBMS offers  text
      editing  facilities  to  assist  the user in the preparation of a
      message.   The  recipient  CBMS  stores  the  message  until  the
      recipient  chooses  to  read  it.    Message systems which do not
      provide these minimum functions are not considered CBMS's.

      The intent of the message format standard is to  allow  users  of
      different computer based message systems to send messages to each
      other.    The  standard  does  not  make  demands  on the message
      transfer system except that it transports messages transparently.
      The standard makes some simple demands on the  CBMS.    The  CBMS
      must  recognize  fields  within  the  message,  process fields in
      predetermined ways, create messages  in  the  correct  form,  and
      recognize  and  create  data  elements of messages in the correct
      format.  The standard does not dictate or constrain the  services
      that  the  CBMS  provides for users, or the way that messages are
      stored, represented, manipulated, or presented to the user by the
      CBMS.

      The standard does constrain the format  of  the  message  at  the
      interface  between  systems.   This guarantees that, whatever the
      source of the message, it arrives at the receiving system in  the
      standard   format.      The  message  format  standard  separates
      information into fields so that the CBMS can locate  and  operate
      on  that  information.   The message is converted from the format
      used within the originator's CBMS  to  the  standard  format  (if
      different)  on  leaving  the  originator's  CBMS.  The message is
      converted from the standard format to the format used within  the
      recipient's CBMS (if different) on entering the recipient's CBMS.

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      Specifications.  Federal  Information Processing Standard (FIPS),
      Message Format for Computer Based Message Systems (affixed).

      Qualifications. None

      Implementation Schedule. All  applicable  equipment  or  services
      ordered  on  or after 24 months from the date of issuance of this
      FIPS PUB, and all CBMS development initiated inhouse on or  after
      12  months  from the date of issuance of this FIPS PUB must be in
      conformance with this standard unless a waiver has been  obtained
      in  accordance  with the procedure described below.  An exception
      to this standard is made when procurement actions  are  into  the
      solicitation phase on the date of issuance of this FIPS PUB.

      Waivers.  Heads  of agencies may request that the requirements of
      this standard be waived in instances  where  it  can  be  clearly
      demonstrated  that  there  are  appreciable  performance  or cost
      advantages to be gained and that the  overall  interests  of  the
      Federal  Government  are  best  served  by granting the requested
      waiver.  Such waiver requests will be reviewed by and are subject
      to the approval of the Secretary of Commerce.  The waiver request
      must address the criteria stated above as the  justification  for
      the waiver.

      Forty-five  days should be allowed for review and response by the
      Secretary of Commerce.  Waiver requests shall be submitted to the
      Secretary of Commerce, Washington, D.C. 20230, and labeled  as  a
      Request   for  a  Waiver  to  a  Federal  Information  Processing
      Standard.  No agency shall take any action to  deviate  from  the
      standard  prior  to  the  receipt  of  a waiver approval from the
      Secretary of Commerce.  No agency  shall  begin  any  process  of
      implementation  or acquisition of non-conforming equipment unless
      it has already obtained such approval.

      Where to Obtain Copies. Either paper or microfiche copies of this
      Federal  Information  Processing  Standard,  including  technical
      specifications,  may  be  purchased  from  the National Technical
      Information  Service  (NTIS)  by  ordering  Federal   Information
      Processing Standard Publication (FIPS-PUB-98), Message Format for
      Computer  Based Message Systems.  Ordering information, including
      prices and delivery alternatives, may be obtained  by  contacting
      the   National   Technical   Information  Service  (NTIS),  U. S.
      Department of Commerce, Springfield,  Virginia  22161,  telephone
      number  (703)  487-4650.    Payment  may  be made by check, money
      order, purchase order, credit card, or deposit account.

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                              EXECUTIVE SUMMARY




           The  message  format  specification addresses the problem of
      exchanging  messages  between  different  computer-based  message
      systems  (CBMSs).    This interchange problem can be addressed on
      several  levels.    One  level  specifies  the  physical   inter-
      connections,  another  specifies  how information travels between
      CBMSs, another specifies  form  and  meaning  of  messages  being
      interchanged.    The  highest  level  specifies  operations  on a
      message.  Each of these levels would be covered  by  a  different
      standard.

           This  message format specification addresses only the issues
      of form and meaning of messages at the points in time  when  they
      are  sent  from  one  CBMS and received by another.  Messages are
      composed of fields, containing different classes of  information.
      These  fields  contain  information about the message originator,
      message recipient, subject matter, precedence and  security,  and
      references  to  previous  messages,  as  well  as the text of the
      message.  Standard formats (syntax) for messages provide a  basis
      for  the  contents  of  messages  generated  by  one  CBMS  to be
      processed by another CBMS.  Standard meanings (semantics) for the
      components of a message facilitate standard interpretation  of  a
      message,  so  that  everyone receiving a message gets the meaning
      intended by its sender.

           Each CBMS that implements this message format  specification
      will  be  compatible  with  any  other  CBMS  that implements the
      specification, provided that the use of optional fields and  data
      elements  is  negotiated  in  advance.    This  ensures  that the
      contents of a message posted by one  CBMS  can  be  received  and
      interpreted by a different CBMS.

           This  message  format  specification has been developed as a
      result of examining CBMSs currently  in  use  in  commercial  and
      research  environments.    Three major design perspectives helped
      shape the message format specification.


        o  Viability.    The  message  format  specification   uses
           concepts  that  already work.  It has been designed with
           implementation concerns in mind.

        o  Compatibility.    The   message   format   specification
           contains concepts from existing CBMSs.  For this reason,
           many CBMS would already contain functions and components
           similar  to  those  required  to  implement  the message
           format specification.

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        o  Extensibility.      This  message  format  specification
           defines a broad range of message content components  and
           requires  only an elementary subset of them.  This means
           that even a very simple CBMS can implement  the  message
           format  specification.  The message format specification
           contains a rich  set  of  optional  components  and,  in
           addition,  mechanisms  for  user  extensions  and future
           extensions to the message format specification.


           The  message  format  specification  defines  the  form  and
      meaning  of  message  contents  and their components as they pass
      from one CBMS to another through a message transfer system.   The
      message   format  specification  does  not  address  any  of  the
      following major issues.


        o  Functions or services provided to a user by a CBMS.
                For  example,  the  message  format   specification
                assumes  that  every CBMS allows a user to send and
                receive messages.  It does not specify any  of  the
                details of how a send function or a message-reading
                function  might  work or how it might appear to the
                user.  That is, the  message  format  specification
                neither limits nor mandates functions.

        o  Storage or format of message contents in a CBMS.
                The  message  format specification defines the form
                and contents of messages when they are  transferred
                between  systems.   A CBMS may or may not choose to
                use the same format for internal storage.

        o  Message transfer system protocols.
                The message format specification does  not  specify
                how  a  message  travels  between  CBMSs.   It does
                specify the form of its contents as it  leaves  and
                arrives,  assuming  only  that the message is moved
                transparently by the transfer system.

        o  Message envelopes.
                While a message is traveling between CBMSs,  it  is
                enclosed  in a message envelope.  Message envelopes
                contain all the information about a message that  a
                message transfer system needs to know.  The message
                format  specification does not define the format or
                content of a message envelope.

        o  How message originators and recipients are identified.
                The message format specification does not provide a
                representation scheme for the names or addresses of
                message originators  and  recipients  as  they  are
                known to a CBMS.

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      1.  INTRODUCTION


           A  computer-based message system (CBMS) allows communication
      between "entities" (usually people) using computers.    Computers
      serve  both  to mediate the actual communications between systems
      and to provide users with facilities for creating and reading the
      messages.

           CBMSs have  been  developing  for  over  ten  years.    More
      recently,  CBMSs  have  been one of the bases in industry for the
      introduction of office automation.  A growing number  of  organi-
      zations  use  either  their own or a commercially available CBMS.
      The design and complexity of these systems  vary  widely.    This
      message  format  specification  provides  a basis for interaction
      between different CBMSs by defining the format of messages passed
      between them.



      1.1  Guide to Reading This Document


           The method of presenting the material in this  specification
      is  to  combine  the technical specification with tutorial infor-
      mation.  This approach has been taken to place the  specification
      in context and improve its readability.

           The  core of the technical information in the document is in
      Section 2, "A Simple Model of a CBMS Environment";  Section  3.1,
      "Semantics  of  Message Fields"; Section 4.2, "Overview of Syntax
      Encoding"; and Section 4.3, "Data Element Syntax".  Appendixes  A
      and  B  consolidate  the technical information.  These appendices
      are designed  for  ease  of  reference  and  should  be  read  in
      conjunction   with   the  body  of  the  report  for  a  complete
      understanding of the message format  presented  in  the  specifi-
      cation.

           Section  2  presents  a simple model of operation of a CBMS.
      Section 3 discusses the components of messages and their  meaning
      (semantics),    including    discussions   of   the   recommended
      relationship between message components and CBMS user  functions.
      (See  Section  3.2.)    Section  4  presents  details of the form
      (syntax) required for components of a message.

           Appendix D summarizes the components of  messages  according
      to  whether  they are required or optional for CBMSs implementing
      the message format  specification.    Appendix  E  organizes  the
      message  components  according  to  the  functional  class of the
      components.  Appendix F provides an  overview  of  the  syntactic
      elements defined by this message format specification; Appendix G

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      summarizes  those elements according to whether they are required
      or optional for a CBMS implementing the message  format  specifi-
      cation.  Examples of each syntactic element appear in Appendix H,
      displaying syntax and describing the associated semantics.



      1.2  Vendor-Defined Extensions to the Specification


           This  specification provides the capability of extending the
      range of functionality by the use  of  vendor-defined  qualifiers
      and  vendor-defined  data  elements.    Any  vendor who uses this
      capability to provide services which are  essentially  equivalent
      to  those already designated as required, basic, or optional does
      not comply with the specification.



      1.3  The Scope of the Message Format Specification


           The purpose of  this  message  format  specification  is  to
      present  the  semantics  and syntax to be used for messages being
      exchanged between CBMSs.  Specifically, it defines the following:


        o  The meaning and form of standard fields to  be  used  in
           messages.

        o  Which fields must be present in all messages.

        o  Which fields complying CBMSs must be able to process.

        o  How  messages,  fields, and the data contained in fields
           are represented.



      1.4  Issues Not Within the Scope of the Message Format Specifi-
           cation


           The  message  format  specification  does  not  address  the
      following  issues,  some  of which are being covered by other NBS
      standards development programs  at  the  Institute  for  Computer
      Sciences and Technology (ICST).  (See [BlaR-80] for a description
      of the ICST network protocols program.)


        o  The nature of a message transfer system, except to state
           the assumption that it transfers messages transparently.

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        o  The  form  or  nature  of the protocols used to transfer
           messages (posting, relay, and delivery protocols).

        o  The content and representation of message envelopes.

        o  Representations for unique identifiers  (in  particular,
           message identifiers).

        o  Network and internetwork addressing.

        o  Representations  for  identities  of message originators
           and recipients.

        o  Certain message processing functions that CBMSs  provide
           for  users,  e.g., those concerned with the creation and
           editing of text.

        o  Presentation of messages to users.

        o  Representations for multi-media objects.

        o  Data representation for messages within CBMSs.

        o  Data sharing or any storage management within CBMSs.

        o  Representations for fixed  or  floating  point  numbers.
           



      1.5  Relationship to Other Efforts


           The  message  format specification is based on several docu-
      ments and the current state  of  many  CBMSs  available  both  in
      industry and the research community.  These documents include the
      standardization efforts in the ARPANet [CroD-77, PosJ-79] and the
      CCITT,  proposed  ISO  and  ANSI  header  format standards [TasG-
      80, ISOD-79], the work of IFIPS Working Group  6.5,  and  various
      papers  about the general nature of mail systems, addressing, and
      mail delivery.  (See [FeiE-79] for references.

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      2.  A SIMPLE MODEL OF A CBMS ENVIRONMENT


           In  order  to provide a framework for presenting the message
      format specification, this section describes a simple  functional
      model for a CBMS.  The model provides a high-level description of
      both  user  facilities  and  system architecture.  Discussions of
      messages, message originators, and message  recipients  serve  to
      further clarify the nature of a CBMS.

           A  CBMS permits the transfer of a message from an originator
      to a recipient.  "Originator" and "recipient" are used  in  their
      normal  English  senses.    (See Section 2.4.)  A message (in its
      most abstract definition) is simply a unit of communication  from
      an  originator  to a recipient.  A CBMS offers several classes of
      functions to its users:


        o  Message Creation:  The  facilities  used  by  a  message
           originator  to  create messages and specify to whom they
           are to be sent.

        o  Message Transfer: The facilities used to convey  a  mes-
           sage to its recipient(s).

        o  Recipient  Processing:  The facilities used by a message
           recipient to process messages that have arrived.


           These classes of functions are presented in more  detail  in
      Section 3.2.

           CBMSs  differ  from  other  office automation/communications
      systems in a number of ways.


        o  Unlike other types of  electronic  communications,  CBMS
           messages  are  sent  to  particular  individuals, not to
           stations or telephone sets.  If a recipient moves  to  a
           different  location, messages sent to that recipient are
           delivered to the recipient at the new location.

        o  Transmission of CBMS  messages  is  asynchronous.    The
           recipient's  system  need not be available when the mes-
           sage leaves the originator's  system.    That  is,  CBMS
           message transfer facilities are store-and-forward.

        o  CBMS  messages can contain a wide variety of data.  They
           are not constrained to any single kind of communication.
           CBMS messages are often simple  memoranda  but  are  not
           restricted to text.  A CBMS message may contain any kind

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           of  data  that  an originator wishes to send to a recip-
           ient.  By contrast, Teletex  systems  and  communicating
           word  processors  handle  the  transfer  of  final  form
           documents; compatible communicating word processors  can
           exchange  documents in editable form; Telex and TWX deal
           in unformatted text.

        o  CBMSs offer message creation facilities as an  important
           part  of  the  system.  CBMSs assist users in the prepa-
           ration of messages by  having  text  editing  facilities
           available  and allowing users to include data stored on-
           line in messages.  Some CBMSs also  interface  to  other
           office  automation  facilities,  such  as formatters and
           spelling correctors.  This is not true of Telex, TWX, or
           similar services.

        o  CBMSs offer recipient processing facilities as an impor-
           tant part of the system.  This is not true of most other
           forms of electronic communications.  For example,  Telex
           and TWX systems simply print messages on paper when they
           are  received,  without  retaining a copy in the system.
           (Teletex systems are similar to Telex systems, but  some
           can  retain  a  copy  of the document in local storage.)
           Communicating  word  processors   might   notify   their
           operators  that  a  document  has  been  received and is
           stored on-line, but they offer  little  in  the  way  of
           other recipient processing facilities.  Most CBMSs offer
           at least the following recipient processing facilities:


             .  The  ability  to retain a copy of a message on-line
                after it has been read.

             .  The ability to examine or  delete  stored  messages
                individually.

             .  The ability to organize messages using some form of
                electronic "file folder."

             .  The  ability  to  determine  if a message is recent
                (has arrived since the last time the recipient used
                the CBMS) or unseen (has never been examined by the
                recipient).

             .  The  ability  to  summarize  stored  messages.    A
                summary   usually   includes  information  such  as
                whether the message is recent or  unseen,  when  it
                was  received,  its length, who it is from, and its
                subject.

             .  The ability to retrieve a stored message based upon

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                one  or  more of its attributves (for example, when
                the message was received, whether  or  not  it  has
                been  seen  or deleted, and the values contained in
                its fields).

             .  A forward facility that allows users to include all
                or part of a message in a new outgoing message.

             .  A reply facility that allows users to  answer  mes-
                sages  without having to enter a new list of recip-
                ients.



      2.1  Logical Model of a CBMS


           CBMS facilities for message creation, transfer,  and  recip-
      ient  processing  are  reflected  in  a  logical  model of a CBMS
      developed by IFIP Working Group 6.5.  (An  essentially  identical
      model  is  being  used  by  CCITT  Study  Group  VII, Question 5,
      regarding  Message  Handling  Systems [CCIT-82].)     The   model
      consists  of  a  Message  Transfer  System  and  a number of User
      Agents.  (See Figure 1.)



                    |                  |
                    |     *************     |
      *********  ------>  *  Message  *  ------->  *********
      * User  *  Posting  * Transfer  *  Delivery  * User  *
      * Agent *  Protocol *  System   *  Protocol  * Agent *
      *********  <------- *************  <-------  *********
                    |                       |
                    |                       |
                 Posting                Delivery
                  Slot                    Slot

                          Message Flow
      Originator --------------------------------> Recipient



      FIG. 1.  LOGICAL MODEL OF A COMPUTER-BASED MESSAGE SYSTEM


           A User Agent (UA) is a functional entity that acts on behalf
      of a user, assisting with creating and  processing  messages  and
      communicating with the Message Transfer System.

           The Message Transfer System(MTS) is an entity that accepts a

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      message from its originator's User Agent and ultimately passes it
      to  each  of  its  recipients' User Agents.  The Message Transfer
      System may perform routing and storage functions  (among  others)
      in order to accomplish its task.

           Transferring  a  message  from an originator's User Agent to
      the Message Transfer System is called Posting;  the  originator's
      User  Agent  and  Message  Transfer  System  engage  in a Posting
      Protocol in order to accomplish Posting.  Transferring a  message
      from  the  Message Transfer System to a recipient's User Agent is
      called Delivery; the recipient's User Agent and Message  Transfer
      System  engage  in  a  Delivery  Protocol  in order to accomplish
      Delivery.

           The point at which responsibility for a  message  is  trans-
      ferred  is called a Slot.  The Posting Slot is the point at which
      responsibility for a message passes  from  an  originator's  User
      Agent  to  the  Message Transfer System; the Delivery Slot is the
      point at which responsibility  for  a  message  passes  from  the
      Message Transfer System to a recipient's User Agent.

           The  model  divides  messages  into  two  parts, the message
      content and the message envelope.  The  message  content  is  the
      information  that the originator wishes to send to the recipient;
      this message format specification deals solely with  the  message
      content.    The  message envelope consists of all the information
      necessary for the Message Transfer System to  do  its  job;  this
      message   format  specification  does  not  specify  the  message
      envelope.  Some of the data appearing  on  the  message  envelope
      could  be  redundant with some data found in the message content.
      The Message Transfer  System  is  not  expected  to  examine  the
      message content unless it is told to do so by the originator's or
      recipient's User Agent.

           This  message format specification places no restrictions on
      the Message Transfer System itself, except that  it  be  able  to
      transfer  messages  between originating and receiving UAs without
      reading or altering the contents  of  messages  unless  otherwise
      instructed by the UAs.  In addition, this message format specifi-
      cation  does  not dictate the form or nature of any protocol used
      by the Message Transfer System.   Finally,  this  message  format
      specification does not specify the content or form of the message
      envelope.   That is, the message format specification defines the
      format for the contents of messages, not the manner in which they
      are transmitted.

           Many of today's commercially available CBMSs incorporate all
      of the facilities  represented  in  the  logical  model.    Their
      architectures  may  reflect  the economies that can be taken when
      implementing systems  that  are  self-contained.    For  example,
      stand-alone  systems  that  store  messages  in  a single central

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      database  require  no  Message Transfer System; an implementation
      may integrate software for User Agent and Message Transfer System
      functions, doing away with Posting or Delivery Protocols.



      2.2  Relationship to the ISO Reference Model for Open Systems
           Interconnection


           Subcommittee TC97/SC16 of the International Organization for
      Standardization  (ISO)  has  developed  a  reference  model   for
      describing communications between "open" systems [ISOD-82].  This
      model  is  known  as  the  ISO  Reference  Model for Open Systems
      Interconnection (OSI).  It divides communications protocols  into
      seven layers, ranging from physical interconnection at the lowest
      layer to data exchange by application programs at the top.

           This message format specification deals with data used by an
      application  within  a  system.    Thus, the message format being
      specified here is not a protocol.  Since it is not a protocol, it
      lies outside of the model for open systems interconnection.  User
      Agents are application layer entities (layer 7), however, and the
      protocols used by a message transfer system are above the session
      layer (layer 5).



      2.3  Messages and Fields


           A message is a unit of communication from an originator to a
      recipient.  A message consists of a series of  components  called
      fields.   Fields can be described according to their meaning in a
      message (semantics) and according to the format required for them
      in a message (syntax).

           Semantically, a field is just a component of a message;  the
      meanings  of particular fields are defined by this message format
      specification.  Syntactically, a field is a unit  of  data  whose
      form is defined by this message format specification.  Additional
      fields can be defined by users or vendors as long as they conform
      to  the  syntactic  and  semantic  rules that this message format
      specification defines for additional fields.

           (A note on terminology: A  message  consists  of  components
      called  fields.  The words "message" and "field" are used both in
      the informal sense  of  the  previous  sentence  and  in  a  more
      restricted  sense  as names of particular syntactic elements.  As
      syntactic  element  names,   Message   and   Field   are   always
      capitalized.)

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           Some  CBMS functions are based on the contents of particular
      fields; other functions (such as the ability to read  a  message)
      may  have  little  to do with the fields themselves.  Section 3.2
      discusses some of  the  specific  functions  that  a  CBMS  might
      provide  to  users  and  the  fields that must be used to support
      those functions.



      2.4  Message Originators and Recipients


           This message format specification refers to  message  origi-
      nators  and recipients.  These terms were defined functionally in
      Figure 1.  When the message format specification  refers  to  the
      identity  of  a  message  originator or recipient, it means "that
      information which uniquely identifies the message  originator  or
      recipient  within  the  domain of the given message system."  The
      syntax and semantics of message addressing  are  not  within  the
      scope of the message format specification.

           Originators  and  recipients can be people, roles, processes
      or groups.

           People.  People as originators and recipients  are  specific
      individuals.

           Roles.    Roles  identify  functions within organizations as
      opposed to the  specific  individuals  who  perform  them.    For
      example,  consider  a  newspaper  that  produces both morning and
      evening editions and therefore operates with more than one shift.
      Someone wishing to contact the city desk would send a message  to
      the  city  desk  role rather than trying to determine exactly who
      was assigned to the city desk at a specific time.    (Of  course,
      messages  can usually be sent to the individuals directly whether
      or not they are actually performing a role at the time.)

           Processes.  A process in a computer could serve as either an
      originator or a recipient for messages.  A computer system  might
      originate  a  message  to  notify a recipient about the status of
      some task.  For example, an archive utility  could  notify  users
      about  files  that  have been archived; a distributed file system
      could notify a user that a remote file has been  deposited  on  a
      local file system.  Messages could be used by computer systems to
      warn  about  some  impending  condition  or  even  to monitor the
      performance of the computer itself.  Some computer processes  may
      also  be  message  recipients,  taking  action based upon message
      contents.

           In addition, some CBMSs allow messages to be sent to groups.
      A group is a predefined list of  message  recipients.    Using  a

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      group   name  as  a  recipient  permits  message  originators  to
      designate a potentially large number of recipients using a single
      recipient identifier.  This makes using the CBMS more  convenient
      and accurate.

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      3.  SEMANTICS


           This  section discusses two major topics, message processing
      functions and message field meanings.  Section 3.1 describes  the
      six  functional  groups of message fields.  The functional groups
      are Origination, Dates, Recipients,  Cross-referencing,  Message-
      handling, and Message-contents.  They are explained more fully in
      Section 3.1.1, along with detailed discussion of the semantics of
      all  the  fields in each functional group.  Section 3.2 describes
      message processing functions whose  operation  is  based  on  the
      meanings of particular message fields.



      3.1  Semantics of Message Fields


           The  definition  of  a  message  is  discussed  generally in
      Sections 1 and 2.  Semantically valid messages must  contain  one
      From  field,  one  To field, and one Posted-Date field.  They may
      contain, in addition, any number of other  fields,  depending  on
      the  processing  and  functions  supplied  by  the originating or
      receiving CBMS.  (Section  3.2  describes  classes  of  functions
      supplied by CBMSs.)


      3.1.1  Types of fields


           Message  receiving programs are required to interpret fields
      according to the semantics described in  the  remainder  of  this
      section.  The message fields defined in this document are grouped
      into the following functional categories.


        o  Originator  fields  indicate who or what participated in
           the creation of the message and where replies should  be
           directed.  (See Section 3.1.3.)

        o  Date fields record when events take place, for a variety
           of events, such as message creation or expiration.  (See
           Section 3.1.5.)

        o  Recipient  fields  indicate  who  or what is intended to
           receive a message.  (See Section 3.1.4.)

        o  Cross-reference fields label a message or refer to other
           messages.  (See Section 3.1.6.)

        o  Message-handling fields record the  type  of  service  a

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           message's  sender requested of a message transfer system
           or indicate how the message should  be  treated  by  its
           recipients.  (See Section 3.1.7.)

        o  Message-content   fields   either  contain  the  primary
           content of a message, or index the message, or summarize
           the message.  (See Section 3.1.8.)

        o  Extension fields provide mechanisms  for  extending  the
           message format specification.  (See Section 3.1.9.)


      3.1.2  Semantic Compliance Categories


           For purposes of determining whether a CBMS complies with the
      semantic  requirements of this message format specification, mes-
      sage fields have been divided into three categories:


      REQUIRED  These fields must be present in all messages  and  must
                be  processed  by message receiving programs as defined
                by the message format specification.

      BASIC     These fields need not be present in  all  messages  but
                when  they do appear, they must be processed by message
                receiving programs as defined  by  the  message  format
                specification.

      OPTIONAL  These  fields  need  not be present in all messages and
                may be ignored by  message  receiving  programs.    The
                exact  meaning  of  "ignored"  is  not specified by the
                message format specification.   However,  a  CBMS  must
                recognize  the existence of an optional field (that is,
                optional fields should not cause errors) and  must  not
                process the field in a manner contrary to the semantics
                defined  for  that field by the message format specifi-
                cation.  It is left to the discretion of a  recipient's
                CBMS  what  action is to be taken when an instance of a
                locally unimplemented optional field is detected.


           (Syntactic compliance is defined in Section 4.1.2.)


      3.1.3  Originator fields


           A message originator may be  a  person,  role,  or  process.
      Originator fields identify a message's author, who is responsible
      for   the   message,   who   or  what  sent  it,  and  where  any
      replies should be directed.  (See Section 2.4.)

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      From                     (REQUIRED)

                This  field  contains the identity of the originator(s)
                taking formal responsibility for  this  message.    The
                contents  of  the  From field is to be used for replies
                when no Reply-to field appears in a message.

      Reply-To                 (BASIC)

                This field identifies any recipients of replies to  the
                message.

      Author                   (OPTIONAL)

                This  field  identifies the individual(s) who wrote the
                primary contents of the message.   Use  of  the  Author
                field  is  discouraged  when the contents of the Author
                field and the From field would be completely redundant.

      Sender                   (OPTIONAL)

                This field identifies the agent who sent  the  message.
                It is used either when the sender is not the originator
                responsible  for the message or to indicate who among a
                group  of  originators  responsible  for  the   message
                actually   sent  it.    Use  of  the  Sender  field  is
                discouraged when the contents of the Sender  field  and
                From  field  would be completely redundant.  The sender
                field may specify  only  one  originator  identity  and
                appear only once in a message.


      3.1.4  Recipient fields


           Message  recipients  may  be  people,  roles,  processes, or
      groups.  (See Section 2.4).  Recipient  fields  identify  who  or
      what is to receive the message.

      To                       (REQUIRED)

                This  field  identifies  the  primary  recipients  of a
                message.

      Bcc                      (OPTIONAL)

                This  field  identifies  additional  recipients  of   a
                message  (a  "blind carbon copies" list).  The contents
                of this field are not to be included in copies  of  the
                message  sent  to the primary and secondary recipients.
                See section 3.2.1 for further discussion of the use  of
                blind carbon copies lists.

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      Cc                       (BASIC)

                This field identifies secondary recipients of a message
                (a "carbon copies" list).

      Circulate-Next           (OPTIONAL)

                This field is used in conjunction with the Circulate-To
                field.    (See  Section  3.2.6.1.)    It identifies all
                recipients in a circulation list who have not  received
                the message.

      Circulate-To             (OPTIONAL)

                This   field  identifies  recipients  of  a  circulated
                message.   (See  Section  3.2.6.1.)    It  is  used  in
                conjunction with the Circulate-Next field.


      3.1.5  Date fields


           Date  fields  for two kinds of uses are provided.  Dates can
      be associated with some event in the history  of  a  message  and
      dates  can  delimit  the span of time during which the message is
      meaningful (its life span).

      Posted-Date              (REQUIRED)

                This field contains the  posting  date,  which  is  the
                point  in  time  when  the  message  passes through the
                posting slot into a message transfer system.  Only  one
                Posted-Date field is permitted in a message.

      Date                     (OPTIONAL)

                This   field   contains   a  date  that  the  message's
                originator wishes to associate with  a  message.    The
                Date field is to the Posted-Date field as the date on a
                letter is to the postmark added by the post office.

      End-Date                 (OPTIONAL)

                This  field  contains the date on which a message loses
                effect.  (See also Section 3.2.5.)

      Received-Date            (OPTIONAL)

                This field is also called Delivery date.    This  field
                may  be  added  to a message by the recipient's message
                receiving program.  It indicates when the message  left

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                the delivery system and entered the recipient's message
                processing domain.

      Start-Date               (OPTIONAL)

                This  field  contains the date on which a message takes
                effect.  (See also Section 3.2.5.)

      Warning-Date             (OPTIONAL)

                This field is used either alone or in conjunction  with
                an  End-Date  field.    It  contains one or more dates.
                These dates could  be  used  by  a  message  processing
                program  as  warnings of an impending end-date or other
                event.  (See also Section 3.2.5.)


      3.1.6  Cross-reference fields


           Cross-reference fields can be used to identify a message and
      to provide cross-references to  other  messages.    (See  Section
      3.2.4.)

      In-Reply-To              (OPTIONAL)

                This  field designates previous correspondence to which
                this message is a reply.  The usual  contents  of  this
                field  would be the contents of the Message-ID field of
                the message(s) being replied to.

      Message-ID               (OPTIONAL)

                This field contains a unique identifier for a  message.
                This  identifier is intended for machine generation and
                processing.   Further  definition  appears  in  Section
                3.2.4.1.    Only one Message-ID field is permitted in a
                message.

      Obsoletes                (OPTIONAL)

                This field identifies one or more  messages  that  this
                one replaces.

      Originator-Serial-Number (OPTIONAL)

                This field contains one or more serial numbers assigned
                by  the  message's  originator.  Messages with multiple
                recipients  should  have  the   same   value   in   the
                Originator-Serial-Number field.

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      References               (OPTIONAL)

                This  field  identifies  other correspondence that this
                message  references.    If  the  other   correspondence
                contains  a  Message-ID  field,  the  contents  of  the
                References field must be the message identifier.


      3.1.7  Message-handling fields


           Message-handling fields describe aspects of how a message is
      to be handled or categorized.

      Precedence               (OPTIONAL)

                This  field  indicates  the  precedence  at  which  the
                message  was posted.  Ordinarily, message precedence or
                priority is a service request  to  a  message  transfer
                system.    A  message  originator, however, can include
                precedence information in a message.   One  example  of
                precedence  categories  are  those  used  by  the  U.S.
                Military: "ROUTINE,"  "PRIORITY,"  "IMMEDIATE,"  "FLASH
                OVERRIDE,"  and "EMERGENCY COMMAND PRECEDENCE."

      Message-Class            (OPTIONAL)

                This  field  indicates  the  purpose of a message.  For
                example, it might contain values  indicating  that  the
                                                             1
                message is a memorandum or a data-base entry. 

      Reissue-Type             (OPTIONAL)

                This   field   is  used  in  conjunction  with  message
                encapsulating  (see  Section  3.2.2)  to  differentiate
                between messages being assigned or redistributed.

      Received-From            (OPTIONAL)

                This  field  contains  a  record  of  a  message's path
                through   a   message    transfer    system.        The
                recipient's  message receiving program could store here
                any information about the  transfer  that  it  obtained
                from a message transfer system.
      _______________

        1
         The message format specification is not intended to be used as
      a  specification  for  exchanging  data-base  records.  Messages,
      however, sometimes contain data from or for a database.

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      3.1.8  Message-content fields


           The   intent   of  most  messages  is  to  communicate  some
      particular information from originator  to  recipient.    Several
      fields in a message are designed to contain that information.

      Subject                  (BASIC)

                This  field  contains  any  information  the originator
                provided to summarize or indicate  the  nature  of  the
                message.

      Text                     (BASIC)

                This field contains the primary content of the message.

      Attachments              (OPTIONAL)

                This  field  contains  additional  data  accompanying a
                message.  It is similar in intent to  enclosures  in  a
                conventional mail system.

      Comments                 (OPTIONAL)

                This  field  permits  adding  comments  to  the message
                without  disturbing  the  original  contents   of   the
                message.

      Keywords                 (OPTIONAL)

                This  field  contains  keywords  or  phrases for use in
                retrieving a message.


      3.1.9  Extensions


           This message  format  specification  allows  two  additional
      types  of  fields,  vendor-defined  fields  and  as-yet-undefined
      (extension) fields that will be introduced by extensions to  this
      message format specification.


      vendor-defined-field
                Any  field  not defined in this message format specifi-
                cation or any extension or successor to it is a vendor-
                defined field.  Names for vendor-defined  fields  could
                be  preempted  by  extensions  to  this  message format
                specification.

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      extension-field
                Any  field that is defined in a document published as a
                formal extension or replacement to this message  format
                specification.



      3.2  Message Processing Functions


           A  CBMS  provides three basic classes of functions: creating
      messages, transmitting messages to  their  recipient,  and  post-
      receipt  processing.    Although the message format specification
      does not define the number or nature of user functions in  CBMSs,
      the  meanings  for  the  fields  clearly  assume certain kinds of
      functions.  For example, fields specifying recipients of  replies
      to messages assume some kind of reply function; fields specifying
      message life span assume some kind of date processing functions.

           This  section  provides  more  detail on the processing that
      might be done by these kinds of functions, discussing the message
      fields that would be used and how  they  would  be  used.    (See
      summary in Table 1.)



      Processing Function    Fields Involved

      Message creation       Author, From, Sender, To,
        and posting          Cc, Bcc
      Message reissuing      Reissue-Type
      Reply generation       Reply-To
      Cross-referencing      Message-ID, In-Reply-To, References,
                             Obsoletes, Originator-Serial-Number
      Life span functions    Start-Date, End-Date,
                             Warning-Date
      Recipient processing   Circulate-To, Circulate-Next



      TABLE 1.  FIELDS USED IN MESSAGE PROCESSING FUNCTIONS


      3.2.1  Message creation and posting


           Messages  can  be  created  either  by reissuing an existing
      message to a new recipient (see Section 3.2.2) or by  creating  a
      new  message.    The  process of message creation might mean that
      some fields of a new message are filled in from the  contents  of
      some  other  message.  Reply functions (Section 3.2.3) provide an
      example of this.

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           Different  individuals could be involved in different phases
      of originating a message: creating it, taking responsibility  for
      it,  and  explicitly  interacting  with  a CBMS to send it to its
      recipient.  One or more individuals may create  a  message  (that
      is,  write, but not necessarily enter it into the CBMS); they are
      said to be the message's authors, identified by the Author field.
      One or more individuals may take responsibility for its  contents
      and  the  decision  to  post  it; they are identified by the From
      field.  One individual explicitly posts  a  given  message;  this
      person  is  called the message's sender (identified by the Sender
      field).

           The sender and author(s) are often, but not always,  respon-
      sible  for the message.  A common case in which the sender is not
      responsible for the message is when a secretary enters and  posts
      messages  for someone else.  An example of a situation in which a
      message's author is not responsible for  the  message  itself  is
      when  an  administrative assistant prepares a report that is sent
      under a manager's signature.

           The use of the Cc field is  identical  to  current  business
      practice.  This field contains the formal secondary recipients of
      the message.

           Messages  containing  Bcc  fields  are  treated specially by
      CBMSs.  The contents of this field are not included in copies  of
      the  message sent to the recipients other than the originator who
      are not included in the Bcc field itself.  Some  systems  include
      the  contents  of  the  Bcc  field only in the originator's copy;
      others include all or part of the Bcc field in the copies sent to
      the recipients indicated in the Bcc field.    This  specification
      does not indicate exactly how the Bcc field is to be treated.


      3.2.2  Message reissuing and forwarding


           Reissuing and forwarding both serve the general user goal of
      passing  a  message on to a new set of recipients.  Forwarding is
      the term used for an informal mechanism, which CBMSs implement by
      copying some or all of the original message into the contents  of
      a  field  in  the  new message.  Reissuing is the term used for a
      formal mechanism to ensure that the message being passed on never
      loses its integrity as a previously  sent  message.    CBMSs  use
      reissuing  to implement several different functions, depending on
      the purposes being served:


        o  Redistribution.  Making others aware of the complete and
           unaltered contents of the message.

Top       Page 33 
        o  Assignment.  Delegating the responsibility for a message
           to somebody else.


      These purposes are exemplified in Figure 2.

           When  a  CBMS examines a forwarded message, it cannot always
      distinguish  the  old  message  from  what  was  added  when  the
      forwarding  took  place.   In addition, the forwarded information
      might no longer have the form of a  message.    This  is  usually
      because  the format of the message has been changed (for example,
      to pure unformatted text).  (See Figure 2 for an example of how a
      CBMS might forward a message.)  In contrast, a  reissued  message
      can  always  be  separated  from  its enclosing message and never
      loses its identity as a correctly formed message.

           This  specification  provides  the  Reissue-Type  field  for
      supporting  reissuing.  Forwarding, since it is an informal means
      of  serving  the  purpose  of  passing  on  information,  has  no
      supporting fields in the specification.

           This  specification  provides  for  reissuing of messages by
      encapsulating.  This method embeds the  entire  original  message
      inside  a  new  message.  Encapsulating adds structure around the

             2
      message .  This allows any part of it to be easily extracted.

           This  procedure for passing on previously sent messages is a
      matter of organizational policy  and  has  authentication  as  an
      associated  issue.   Each organization must decide if the CBMS it
      acquires should support reissuing or simply supply forwarding.


      3.2.2.1  Redistribution

           Redistribution is a CBMS function for sending  the  original
      contents  of a message intact and unchanged to new recipients.  A
      redistributed message is identical to the original  message  with
      the  exception  of  added  information  about the reissuing.  For
      reissuing with this purpose, the Reissue-Type field contains  the
      ASCII  string  "Redistribution."    The original message has been
      included directly in a new message.  (See Figure 2.)


      _______________

        2
         A message can contain another message, and  that  message  can
      contain another message, and so on to any depth of encapsulating.
      This can occur by reissuing a message repeatedly.

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                            The Original Message
      John Doe wishes Jane Jones to get a copy of the following
      message:
                      Message:
                        Field: From "Jean Smith"
                        Field: Posted-Date "27 January 1983"
                        Field: To "John Doe"
                        Field: Subject "Next Project Meeting"
                        Field: Text "The agenda for ..."

                               Redistribution
      Message:
        Field: From "John Doe"                  John Doe is responsible
        Field: Posted-Date "28 January 1983"    for the redistribution.
        Field: To "Jane Jones"
        Field: Reissue-Type "Redistribution"    This message directly
        Message:                                incorporates a
          Field: From "Jean Smith"              redistributed message.
          Field: Posted-Date "27 January 1983"
          Field: To "John Doe"
          Field: Subject "Next Project Meeting"
          Field: Text "The agenda for ..."

                                 Forwarding
      Message:
        Field: From "John Doe"
        Field: Posted-Date "28 January 1983"
        Field: To "Jane Jones"
        Field: Text                             A realization of the
          "From Jean Smith                      original message is
           To John Doe                          copied into the Text field.
           Sent on 27 January 1983              Note that John's CBMS
           Subject Next Project Meeting         has chosen to represent
                                                it as a text string.
           The agenda for ..."



      FIG. 2.  MESSAGE FORWARDING AND REDISTRIBUTION


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