RFC 8322
Resource-Oriented Lightweight Information Exchange (ROLIE)
Pages: 43
Proposed Standard
Proposed Standard
Part 1 of 2 – Pages 1 to 20
Internet Engineering Task Force (IETF) J. Field Request for Comments: 8322 Pivotal Category: Standards Track S. Banghart ISSN: 2070-1721 D. Waltermire NIST February 2018 Resource-Oriented Lightweight Information Exchange (ROLIE)Abstract
This document defines a resource-oriented approach for security automation information publication, discovery, and sharing. Using this approach, producers may publish, share, and exchange representations of software descriptors, security incidents, attack indicators, software vulnerabilities, configuration checklists, and other security automation information as web-addressable resources. Furthermore, consumers and other stakeholders may access and search this security information as needed, establishing a rapid and on-demand information exchange network for restricted internal use or public access repositories. This specification extends the Atom Publishing Protocol and Atom Syndication Format to transport and share security automation resource representations. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8322.
Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents
1. Introduction ....................................................3 2. Terminology .....................................................4 3. XML-Related Conventions .........................................5 3.1. XML Namespaces .............................................5 3.2. RELAX NG Compact Schema ....................................5 4. Background and Motivation .......................................5 5. ROLIE Requirements for the Atom Publishing Protocol .............7 5.1. AtomPub Service Documents ..................................7 5.1.1. Use of the "app:workspace" Element ..................8 5.1.2. Use of the "app:collection" Element .................8 5.1.3. Service Document Discovery ..........................9 5.2. Category Documents .........................................9 5.3. Transport Layer Security ..................................10 5.4. User Authentication and Authorization .....................10 5.5. "/" (Forward Slash) Resource URL ..........................11 5.6. HTTP Methods ..............................................11 6. ROLIE Requirements for the Atom Syndication Format .............11 6.1. Use of the "atom:feed" Element ............................11 6.1.1. Use of the "atom:category" Element .................13 6.1.2. Use of the "atom:link" Element .....................14 6.1.3. Use of the "atom:updated" Element ..................15 6.2. Use of the "atom:entry" Element ...........................16 6.2.1. Use of the "atom:content" Element ..................17 6.2.2. Use of the "atom:link" Element .....................17 6.2.3. Use of the "rolie:format" Element ..................18 6.2.4. Use of the "rolie:property" Element ................19 6.2.5. Requirements for a Standalone Entry ................20
7. Available Extension Points Provided by ROLIE ...................21 7.1. The Category Extension Point ..............................21 7.1.1. General Use of the "atom:category" Element .........22 7.1.2. Identification of Security Automation Information Types ..................................22 7.2. The "rolie:format" Extension Point ........................24 7.3. The Link Relation Extension Point .........................24 7.4. The "rolie:property" Extension Point ......................24 8. IANA Considerations ............................................26 8.1. XML Namespaces and Schema URNs ............................26 8.2. ROLIE URN Sub-namespace ...................................26 8.3. ROLIE URN Parameters ......................................27 8.4. ROLIE Information Types Registry ..........................29 9. Security Considerations ........................................29 10. Privacy Considerations ........................................31 11. References ....................................................32 11.1. Normative References .....................................32 11.2. Informative References ...................................34 Appendix A. RELAX NG Compact Schema for ROLIE .....................37 Appendix B. Examples of Use .......................................37 B.1. Service Discovery ..........................................37 B.2. Feed Retrieval .............................................40 B.3. Entry Retrieval ............................................42 Acknowledgements ..................................................43 Authors' Addresses ................................................431. Introduction
This document defines a resource-oriented approach to security automation information sharing that follows the Representational State Transfer (REST) architectural style [REST]. In this approach, computer security resources are maintained in web-accessible repositories structured as Atom Syndication Format [RFC4287] Feeds. Within a given Feed, which may be requested by the consumer, representations of specific types of security automation information are organized, categorized, and described. Furthermore, all collections available to a given user are discoverable, allowing the consumer to search all available content they are authorized to view, and to locate and request the desired information resources. Through the use of granular authentication and access controls, only authorized consumers may be permitted the ability to read or write to a given Feed. The goal of this approach is to increase the communication and sharing of security information between providers and consumers that can be used to automate security processes (e.g., incident reports, vulnerability assessments, configuration checklists, and other security automation information). Such sharing allows human
operators and computer systems to leverage this standardized communication system to gather information that supports the automation of security processes. To support new types of security automation information being used as time goes on, this specification defines a number of extension points that can be used either privately or globally. These global extensions are IANA-registered by Resource-Oriented Lightweight Information Exchange (ROLIE) extension specifications and provide enhanced interoperability for new use cases and domains. Sections 5 and 6 of this document define the requirements for XML representations of ROLIE; other equivalent representations (e.g. JSON) may be described by other documents. An overview of the extension system is provided in Section 7. Implementers seeking to provide support for specific security automation information types should refer to the specification for that domain as described by the IANA registry found in Section 8.4.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. The previous key words are used in this document to define only the requirements for implementations of this specification and are not used for recommendations or requirements for the usage of ROLIE. (In other words, a programmer of a ROLIE server MUST implement a given feature, but a user of that ROLIE server needn't use that feature.) Definitions for some of the common computer-security-related terminology used in this document can be found in Section 2 of [RFC7970]. The following term is unique to this specification: Information Type: A class of security automation information having one or more associated data models. Often, such security automation information is used in the automation of a security process. See Section 7.1.2 for more information.
3. XML-Related Conventions
3.1. XML Namespaces
This specification uses XML namespaces [W3C.REC-xml-names-20091208] to uniquely identify XML element names. It uses the following namespace prefix mappings for the indicated namespace URI: o "app" is used for the "https://www.w3.org/2007/app" namespace defined in [RFC5023]. o "atom" is used for the "https://www.w3.org/2005/Atom" namespace defined in [RFC4287]. o "rolie" is used for the "urn:ietf:params:xml:ns:rolie:1.0" namespace defined in Section 8.1 of this specification.3.2. RELAX NG Compact Schema
Some sections of this specification are illustrated with fragments of a non-normative RELAX NG Compact Schema [RELAX-NG]. The text of this specification provides the definition of conformance. Schema for the "https://www.w3.org/2007/app" and "https://www.w3.org/2005/Atom" namespaces appear in Appendix B of [RFC5023] and Appendix B of [RFC4287], respectively. A complete informative RELAX NG Compact Schema for the new elements introduced by ROLIE is provided in Appendix A of this document.4. Background and Motivation
In order to automate security processes, tools need access to sufficient sources of structured security information that can be used to drive security processes. Thus, security information sharing is one of the core components of automating security processes. Vulnerabilities, configurations, software identification, security incidents, and patch data are just a few of the classes of information that are shared today to enable effective security on a wide scale. However, as the scale of defense broadens as networks become larger and more complex, and the volume of information to process makes humans-in-the-loop difficult to scale, the need for automation and machine-to-machine communication becomes increasingly critical.
ROLIE seeks to address this need by providing four major information-
sharing benefits:
Extensible information type categories and format agnosticism: ROLIE
is not bound to any given data format or category of information.
Instead, information categories are extensible, and Entries
declare the format of the referenced data. In cases where several
formats or serializations are available, ROLIE can use link
relations to communicate how a consumer can access these formats.
For example, clients may request that a given resource
representation be returned as XML, JSON, or in some other format
or serialization. This approach allows the provider to support
multiple isomorphic formats, allowing the consumer to select the
most suitable version.
Open and distributed information sharing: Using the Atom Publishing
Protocol (AtomPub), ROLIE Feeds can easily aggregate Feeds and
accept information posted to them from other sources. Webs of
communicating ROLIE servers form ad hoc sharing communities,
increasing data availability and the ability to correlate linked
data across sources for participating consumers. ROLIE servers
needn't be distributed, however, as large ROLIE repositories can
function as a central collection or federated collections.
Stateless communication model: ROLIE, as a RESTful system, is
stateless. That is, the server doesn't keep track of client
sessions but rather uses link relations for state transitions. In
practice, this means that any consumer can find and share
information at any organizational level and at any time without
needing to execute a long series of requests.
Information discovery and navigation: ROLIE provides a number of
mechanisms to allow clients to programmatically discover and
navigate collections of information in order to dynamically
discover new or revised content. Extensible information types and
other categories provide one way of determining content that is
desirable. Link elements, each with a target URI and an
established relationship type, provide a means for ROLIE providers
to link other information that is relevant to the current Entry
or Feed.
These benefits result in an information-sharing protocol that is
lightweight, interactive, open, and, most importantly, machine
readable.
The requirements in this specification are broken into two major
sections: extensions to AtomPub [RFC5023] and extensions to the Atom
Syndication Format [RFC4287]. All normative requirements in AtomPub
and Atom Syndication are inherited from their respective specifications and apply here unless the requirement is explicitly overridden in this document. In this way, this document may upgrade the requirement (e.g., make a "SHOULD" a "MUST") but will never downgrade a given requirement (e.g., make a "MUST" a "SHOULD").5. ROLIE Requirements for the Atom Publishing Protocol
This section describes a number of restrictions of, and extensions to, AtomPub [RFC5023] that define the use of AtomPub in the context of a ROLIE-based solution. The normative requirements in this section are generally oriented towards client and server implementations. An understanding of the AtomPub specification [RFC5023] is helpful to understand the requirements in this section.5.1. AtomPub Service Documents
As described in Section 8 of [RFC5023], a Service Document is an XML-based document format that allows a client to dynamically discover the Collections provided by a publisher. A Service Document consists of one or more "app:workspace" elements that may each contain a number of "app:collection" elements. The general structure of a Service Document is as follows (from Section 4.2 of [RFC5023]): Service o- Workspace | | | o- Collection | | | | | o- URI, categories, media types | | | o- ... | o- Workspace | | | o- Collection | | | | | o- URI, categories, media types | | | o- ... | o- ... Note that the Internationalized Resource Identifiers (IRIs) in the original diagram have been replaced with URIs.
5.1.1. Use of the "app:workspace" Element
In AtomPub, a workspace, represented by the "app:workspace" element, describes a group of one or more Collections. Building on the AtomPub concept of a workspace, in ROLIE a workspace represents an aggregation of Collections pertaining to security automation information resources. This specification does not restrict the number of workspaces that may be in a Service Document or the specific Collections to be provided within a given workspace. A ROLIE implementation can host Collections containing both public and private information Entries. It is suggested that implementations segregate Collections into different "app:workspace" elements by their client access requirements. With proper naming of workspaces, this reduces the amount of trial and error a human user would need to utilize to discover accessible Collections.5.1.2. Use of the "app:collection" Element
In AtomPub, a Collection in a Service Document, represented by the "app:collection" element, provides metadata that can be used to point to a specific Atom Feed that contains information Entries that may be of interest to a client. The association between a Collection and a Feed is provided by the "href" attribute of the "app:collection" element. Building on the AtomPub concept of a Collection, in ROLIE a Collection represents a pointer to a group of security automation information resources pertaining to a given type of security automation information. Collections are represented as Atom Feeds as per RFC 5023. Requirements specific to Atom Feed are defined in Section 6.1. ROLIE defines specialized data requirements for Collections, Feeds, and Entries containing data related to security automation. The difference between a ROLIE Collection and a non-ROLIE Collection defined in a Service Document can be determined as follows: ROLIE Collection: An app:collection is considered a ROLIE Collection when it contains an "app:categories" element that contains only one "atom:category" element with a "scheme" attribute value of "urn:ietf:params:rolie:category:information-type". Further, this category has an appropriate "term" attribute value as defined in Section 7.1.1. This ensures that a given Collection corresponds to a specific type of security automation information. Non-ROLIE Collection: An app:collection is considered a non-ROLIE Collection when it does not contain an "atom:category" element with a "scheme" attribute value of "urn:ietf:params:rolie:category:information-type".
By distinguishing between ROLIE and non-ROLIE Collections in this
way, implementations supporting ROLIE can host Collections pertaining
to security automation information alongside Collections of other
non-ROLIE information within the same AtomPub instance.
The following are additional requirements on the use of the
"app:collection" element for a ROLIE Collection:
o The child "atom:category" elements contained in the
"app:categories" element MUST be the same set of "atom:category"
elements used in the Atom Feed resource referenced by the
"app:collection" element's "href" attribute value. This ensures
that the category metadata associated with the Collection and the
associated Feed is discoverable in both of these resources.
o The "app:categories" element in an app:collection MAY include
additional "atom:category" elements using a scheme other than
"urn:ietf:params:rolie:category:information-type". This allows
other category metadata to be included.
5.1.3. Service Document Discovery
The Service Document serves as the "head" of a given ROLIE
repository: from the Service Document, all other repository content
can be discovered. A client will need to determine the URL of this
Service Document to discover the Collections provided by the
repository. The client might determine the URL from a web page,
based on out-of-band communication, or through a "service" link
relation in a Feed or Entry Document that the client has already
retrieved. The latter is a typical scenario if the client learns of
a specific Feed or Entry through an out-of-band mechanism and wishes
to discover additional information provided by the repository.
This document does not provide a fully automated discovery mechanism.
A mechanism may be defined in the future that allows automated
clients to discover the URL to use to retrieve a ROLIE Service
Document representing the head of the ROLIE repository.
5.2. Category Documents
As described in Section 7 of [RFC5023], a Category Document is an
XML-based document format that allows a client to dynamically
discover the categories used within AtomPub Service Documents, Atom
Syndication Feeds, and Entry Documents provided by a publisher. A
Category Document consists of one "app:categories" element that
contains a number of inline "atom:category" elements, or a URI
referencing a Category Document.
5.3. Transport Layer Security
ROLIE is intended to be handled with Transport Layer Security (TLS). TLS version 1.2 MUST be supported. TLS 1.2 SHOULD be implemented according to all recommendations and best practices presented in [RFC7525]. It is RECOMMENDED that the most recent published version of TLS be supported. If this version is TLS 1.3 [TLS-1.3], it is suggested that 0-RTT (Zero Round-Trip Time Resumption) not be used, in order to prevent replay attacks. Replay attacks on PUT, POST, or DELETE requests can disrupt repository operation by modifying data unexpectedly. For example, an automated ROLIE repository that updates very frequently may receive a PUT request against a given resource a few times an hour (or more). An attacker may store an early PUT request, and at the end of the resumption window replay the PUT request, reverting the resource to an old version. Not only could an attacker be doing this replay continuously to cause havoc on the server, but the client is completely unaware of the attack taking place. Given the potentially sensitive nature of data handled by ROLIE, all appropriate precautions should be taken at the transport layer to protect forward secrecy and user privacy. The server MUST implement certificate-based client authentication. This MAY be enabled on a workspace-by-workspace basis.5.4. User Authentication and Authorization
Implementations MUST support user authentication. However, a given implementation MAY allow user authentication to be disabled on a Feed-by-Feed or workspace-by-workspace basis. It is recommended that servers participating in an information- sharing consortium and supporting interactive user logins by members of the consortium support client authentication via a federated identity scheme. This document does not mandate the use of any specific user authorization mechanisms. However, service implementers SHOULD support appropriate authorization checking for all resource accesses, including individual Atom Entries, Atom Feeds, and Atom Service Documents.
5.5. "/" (Forward Slash) Resource URL
The "/" resource MAY be supported for compatibility with existing deployments that are using [RFC6546] ("Transport of Real-time Inter-network Defense (RID) Messages over HTTP/TLS"). The following requirements apply only to implementations that support both RFC 6546 and the "/" resource as described above: o Consistent with Erratum ID 3267 [Err3267] for [RFC6546], a client requesting a GET on the "/" resource SHOULD receive an HTTP status code 405 ("Method Not Allowed"). o An implementation MAY provide full support for [RFC6546] such that a POST to the "/" resource containing a recognized RID message is handled correctly as a RID request. Alternatively, a client requesting a POST to "/" MAY receive an HTTP status code 307 ("Temporary Redirect"). In this case, the location header in the HTTP response will provide the URL of the appropriate RID endpoint, and the client may repeat the POST method at the indicated location. If RFC 6546 is unsupported, then a request for the "/" resource may be handled as deemed appropriate by the server.5.6. HTTP Methods
Servers MAY accept request methods beyond those specified in this document. Clients MUST be capable of recognizing and processing any standard HTTP status code, as defined in Section 5 of [RFC5023].6. ROLIE Requirements for the Atom Syndication Format
This section describes a number of restrictions of, and extensions to, the Atom Syndication Format [RFC4287] that define the valid use of the format in the context of a ROLIE implementation. An understanding of the Atom Syndication Format specification [RFC4287] is helpful to understand the requirements in this section.6.1. Use of the "atom:feed" Element
As described in Section 4.1.1 of [RFC4287], an Atom Feed is an XML-based document format that describes a list of related information items. The Atom Feeds provided by a ROLIE service are listed in the service's Service Document through one or more "app:collection" elements. Each Feed Document, represented using the "atom:feed" element, contains a listing of zero or more Entries.
When applied to the problem domain of security automation information sharing, an Atom Feed may be used to represent any meaningful collection of security automation information resources. Each Entry in a Feed represents an individual resource (e.g., a specific checklist, a software vulnerability record). Additional Feeds can be used to represent other collections of security automation resources. As discussed in Section 5.1.2, ROLIE defines specialized data requirements for Feeds containing data related to security automation. The difference between a ROLIE Feed and a non-ROLIE Feed can be determined as follows: ROLIE Feed: For an "atom:feed" to be considered a ROLIE Feed, the "atom:feed" MUST contain only one child "atom:category" element with a "scheme" attribute value of "urn:ietf:params:rolie:category:information-type". This category MUST have an appropriate "term" attribute value as defined in Section 7.1.1. This ensures that a given Feed corresponds to a specific type of security automation information. Non-ROLIE Feed: For an "atom:feed" to be considered a non-ROLIE Feed, the "atom:feed" MUST NOT contain an "atom:category" element with a "scheme" attribute value of "urn:ietf:params:rolie:category:information-type". By distinguishing between ROLIE and non-ROLIE Feeds in this way, implementations supporting ROLIE can host Feeds pertaining to security automation information alongside Feeds of other non-ROLIE information within the same AtomPub instance. This is parallel to the handling of Collections as discussed earlier in this specification (Section 5.1.2).
The following Atom Feed definition represents a stricter definition of the "atom:feed" element defined in [RFC4287] when used as a ROLIE Feed. Any element not specified here inherits its definition and requirements from [RFC4287]. atomFeed = element atom:feed { atomCommonAttributes, (atomAuthor* & atomCategory+ & atomContributor* & atomGenerator? & atomIcon? & atomId & atomLink+ & atomLogo? & atomRights? & atomSubtitle? & atomTitle & atomUpdated & extensionElement*), atomEntry* } The following subsections contain requirements for a ROLIE Feed.6.1.1. Use of the "atom:category" Element
An "atom:feed" can contain one or more "atom:category" elements. In Atom, the naming scheme and the semantic meaning of the terms used to identify an Atom category are application defined. The following are additional requirements on the use of the "atom:category" element when used in a ROLIE Feed: o All member Entries in the Feed MUST represent security automation information records of the provided information type category. o The "atom:feed" MAY include additional "atom:category" elements using a scheme other than "urn:ietf:params:rolie:category:information-type". This allows other category metadata to be included.
6.1.2. Use of the "atom:link" Element
Link relations defined by the "atom:link" element are used to represent state transitions using a stateless approach. In Atom, a type of link relationship can be defined using the "rel" attribute. A ROLIE Feed MUST contain one or more "atom:link" elements with rel="service" and an "href" attribute whose value is a URI that points to an Atom Service Document associated with the Feed. If a client accesses a Feed without first accessing the service's Service Document, a link with the "service" relationship provides a means to discover additional security automation information. The "service" link relationship is defined in the IANA "Link Relations" registry at <https://www.iana.org/assignments/link-relations/>. A Feed can contain an arbitrary number of Entries. In some cases, a complete Feed may consist of a large number of Entries. Additionally, as new and updated Entries are ordered at the beginning of a Feed, a client may only be interested in retrieving the first N Entries in a Feed to process only the Entries that have changed since the last retrieval of the Feed. As a practical matter, a large set of Entries will likely need to be divided into more manageable portions, or pages. Based on Section 3 of [RFC5005], link elements SHOULD be included in all Feeds to support paging using the following link relation types: o "first" - Indicates that the "href" attribute value of the link identifies a resource URI for the furthest preceding page of the Feed. o "last" - Indicates that the "href" attribute value of the link identifies a resource URI for the furthest following page of the Feed. o "previous" - Indicates that the "href" attribute value of the link identifies a resource URI for the immediately preceding page of the Feed. o "next" - Indicates that the "href" attribute value of the link identifies a resource URI for the immediately following page of the Feed.
For example:
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="https://www.w3.org/2005/Atom">
<id>b7f65304-b63b-4246-88e2-c104049c5fd7</id>
<title>Paged Feed</title>
<link rel="self" href="https://example.org/feedA?page=5"/>
<link rel="first" href="https://example.org/feedA?page=1"/>
<link rel="prev" href="https://example.org/feedA?page=4"/>
<link rel="next" href="https://example.org/feedA?page=6"/>
<link rel="last" href="https://example.org/feedA?page=10"/>
<updated>2012-05-04T18:13:51.0Z</updated>
<!-- remainder of the Feed's elements -->
</feed>
Example Paged Feed
A reference to a historical Feed may need to be stable, and/or a Feed
may need to be divided into a series of defined epochs.
Implementations SHOULD support the mechanisms described in Section 4
of [RFC5005] to provide link-based state transitions for maintaining
the archiving of Feeds.
A Feed MAY include additional link relationships not specified in
this document. If a client encounters an unknown link relationship
type, the client MUST ignore the unrecognized link and continue
processing as if the unrecognized link element did not appear. The
definition of new link relations that provide additional state
transition extensions is discussed in Section 7.3.
6.1.3. Use of the "atom:updated" Element
The "atom:updated" element identifies the date and time that a Feed
was last updated.
The "atom:updated" element MUST be populated with the current time at
the instant the Feed was last updated by adding, updating, or
deleting an Entry, or by changing any metadata for the Feed.
6.2. Use of the "atom:entry" Element
Each Entry in an Atom Feed, represented by the "atom:entry" element, describes a single referenced information record, along with descriptive information about its format, media type, and other publication metadata. The following "atom:entry" schema definition represents a stricter representation of the "atom:entry" element defined in [RFC4287] for use in a ROLIE-based Atom Feed as defined in Section 6.1.1. atomEntry = element atom:entry { atomCommonAttributes, (atomAuthor* & atomCategory* & atomContent & atomContributor* & atomId & atomLink* & atomPublished? & atomRights? & atomSource? & atomSummary? & atomTitle & atomUpdated & rolieFormat? & rolieProperty* & extensionElement*) } The notable changes from [RFC4287] are the addition of "rolieFormat" and "rolieProperty" elements. Also, the "atomContent" element is restricted to the atomOutOfLineContent formulation and is now REQUIRED. The following subsections contain requirements for Entries in a ROLIE Feed.
6.2.1. Use of the "atom:content" Element
An "atom:content" element associates its containing Entry with a content resource identified by the "src" attribute. There MUST be exactly one "atom:content" element in the Entry. The "atom:content" element MUST adhere to this definition, which is a stricter representation of the "atom:content" element defined in [RFC4287]: atomContent = element atom:content { atomCommonAttributes, attribute type { atomMediaType }, attribute src { atomUri }, empty } This restricts atomContent in ROLIE to the atomOutOfLineContent formulation presented in [RFC4287]. The "type" attribute MUST identify the serialization type of the content -- for example, "application/xml" or "application/json". A prefixed media type MAY be used to reflect a specific model used with a given serialization approach (e.g., "application/rdf+xml"). The "src" attribute MUST be a URI that can be dereferenced to retrieve the related content data.6.2.2. Use of the "atom:link" Element
Link relations can be included in an Entry to represent state transitions to and from the Entry, as well as to provide links to related information. If there is a need to provide the same information in different data models and/or serialization formats, separate Entry instances can be included in the same Feed or a different Feed. Such an alternate content representation can be indicated using an "atom:link" having a "rel" attribute with the value "alternate". A Feed MAY include additional link relationships not specified in this document. If a client encounters an unknown link relationship type, the client MUST ignore the unrecognized link and continue processing as if the unrecognized link element did not appear. The definition of new link relations that provide additional state transition extensions is discussed in Section 7.3.
6.2.3. Use of the "rolie:format" Element
As mentioned in Sections 1 and 4, a key goal of this specification is to allow a consumer to review a set of published security automation information resources and then identify and retrieve any resources of interest. The format of the data is a key criteria to consider when deciding what information to retrieve. For a given type of security automation information, it is expected that a number of different formats may be used to represent this information. To support this use case, both the serialization format and the specific data model expressed in that format must be known by the consumer. In the Atom Syndication Format, a media type can be defined using the "type" attribute of the "atom:content" element of an "atom:entry". The media type can be fully descriptive of the format of the linked document, such as "application/atom+xml". In some cases, however, a format-specific media type may not be defined. An example might be when "application/xml" is used because there is no defined specific media type for the content. In such a case, the exact data model of the content cannot be known without first retrieving the content. In cases where a specific media type does not exist, the "rolie:format" element is used to describe the data model used to express the information referenced in the "atom:content" element. The "rolie:format" element also allows a schema to be identified that can be used when parsing the content to verify or better understand the structure of the content. When it appears, the "rolie:format" element MUST adhere to this definition: rolieFormat = element rolie:format { atomCommonAttributes, attribute ns { atomUri }, attribute version { text } ?, attribute schema-location { atomUri } ?, attribute schema-type { atomMediaType } ?, empty } The "rolie:format" element MUST provide a "ns" attribute that identifies the data model of the resource referenced by the "atom:content" element. For example, the namespace used may be an XML namespace URI or an identifier that represents a serialized JSON model. The URI used for the "ns" attribute MUST be absolute. The resource identified by the URI need not be resolvable.
The "rolie:format" element MAY provide a "version" attribute that identifies the version of the format used for the related "atom:content" element. The "rolie:format" element MAY provide a "schema-location" attribute, which is a URI that identifies a schema resource that can be used to validate the related "atom:content" element. The "rolie:format" element MAY provide a "schema-type" attribute, which is a media type (as described in [RFC2045]) identifying the format of the schema resource identified by the "schema-location" attribute. The following nominal example shows how these attributes describe the format of the content: <rolie:format ns="urn:ietf:params:xml:ns:iodef-2.0" version="2.0" schema-location= "https://www.iana.org/assignments/xml-registry/schema/iodef-2.0.xsd" schema-type="text/xml"/> The previous element provides an indication that the content of the given Entry is using the Incident Object Description Exchange Format (IODEF) v2 format.6.2.4. Use of the "rolie:property" Element
An "atom:category" element provides a way to associate a name/value pair of categorical information using the "scheme" and "term" attributes to represent the name and using the "label" attribute to represent the value. When used in this way, an "atom:category" allows a specific label to be selected from a finite set of possible label values that can be used to further classify a given Entry or Feed. Within ROLIE, there may be a need to associate additional metadata with an Entry. In such a case, the use of an "atom:category" is not practical to represent name/value data for which the allowed values are unbounded. Instead, ROLIE introduces a new "rolie:property" element that can represent non-categorical metadata as name/value pairs. Examples include content-specific identifiers, naming data, and other properties that allow for unbounded values. There MAY be zero or more "rolie:property" elements in an "atom:entry".
The element MUST adhere to this definition:
rolieProperty =
element rolie:property {
atomCommonAttributes,
attribute name { atomUri },
attribute value { text },
empty
}
The "name" attribute provides a URI that identifies the namespace and
name of the property as a URI.
The "value" attribute is text that provides a value for the property
identified by the "name" attribute.
For example, the nominal element <rolie:property
name="urn:ietf:params:rolie:property:content-id" value="12345"/>
would expose an IODEF ID value contained in a given Entry's content.
The name used in the example also demonstrates the use of a
registered ROLIE property extension, which is described in
Section 7.4.
Implementations MAY use locally defined and namespaced elements in an
Entry in order to provide additional information. Clients that do
not recognize a property with an unregistered "name" attribute MUST
ignore the "rolie:property" element; that is, the client MUST NOT
fail parsing content that contains an unrecognized property.
6.2.5. Requirements for a Standalone Entry
If an Entry is ever shared as a standalone resource, separate from
its containing Feed, then the following additional requirements
apply:
o The Entry MUST have an "atom:link" element with rel="collection"
and href="[URI of the containing Collection]". This allows the
Feed or Feeds of which the Entry is a member to be discovered,
along with the related information the Feed may contain. In the
case where the Entry has multiple containing Feeds, the Entry MUST
have one "atom:link" for each related Feed.
o The Entry MUST declare the information type of the content
resource referenced by the Entry (see Section 7.1.2).
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