1. Introduction

Open Archives Initiative Object Reuse and Exchange (OAI-ORE) defines standards for the description and exchange of Aggregations of Web resources. OAI-ORE introduces the notion of Resource Maps that describe an Aggregation. A Resource Map is a specialization of a Named Graph [Named Graph], which  is a set of triples named by a URI.  This URI makes it possible for other applications to link to or refer to the Resource Map. A Resource Map identifies an Aggregation, it asserts the finite set of constituent resources (the Aggregated Resources) of the Aggregation, and it can express types and relationships pertaining to the Aggregation and its Aggregated Resources. Each Aggregation may be described by one or more Resource Maps, each of which must have exactly one Representation that is a serialization of the Resource Map according to a specific format. The purpose of this document is to specify a serialization for Resource Maps based on and compliant with the Atom syndication format [RFC4287]. This serialization may be referred to as the Resource Map Profile of Atom. Atom-based Resource Maps may be appealing to a number of application domains because of their simplicity and the existence of standard Web feed technology.

The ORE Model imposes constraints on the types of triples that can be expressed in the Resource Map RDF Graph. Although the hierarchical structure of Atom Feeds does not naturally accomodate the expression of aribtrary graphs, the Atom-based serialization of the Resource Map RDF Graph described in this document is capable of expressing the entire range of triples allowed by the ORE Abstract Data Model in Atom. Moreover, Atom-based Resource Maps can automatically and losslessly be transformed into the RDF/XML serializations of Resource Maps as described in the ORE User Guide - Resource Map Implementation in RDF/XML [ORE User Guide RDF/XML].

This specifcation uses concepts and terms introduced in the following ORE documents:

• ORE Specification - Abstract Data Model [ORE Model];
• ORE Specification - Vocabulary [ORE Vocabulary].

Atom representations of Resource Maps are fully compliant with the Atom Syndication Format [RFC4287] and adhere to a specific profile of it:

• Section 2 defines how entities of the ORE Model relate to entities of the Atom model.
• Section 3 and Section 4 restrict the use of some Atom constructs and elements, and specify how to use the extensibility features of Atom to address ORE requirements.

The ORE User Guide - Resource Map Implementation in Atom [ORE User Guide Resource Map] provides Atom implementation guidance that supplement this specification.

1.1 Notational Conventions

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

This specification uses the same shorthands to terms from the XML Infoset [XML Infoset] as used in [RFC4287]: the phrase "Information Item" is omitted when naming Element Information Items and Attribute Information Items. Therefore, when this specification uses the term "element," it is referring to an Element Information Item in Infoset terms. Likewise, when it uses the term "attribute," it is referring to an Attribute Information Item.

This specification uses the common term URI [RFC3986] to mean both IRI [RFC3987] and URI.

1.2 Namespaces

This specification uses the following namespaces and prefixes:

1.3 Compliance

Atom representations of Resource Maps MUST be compliant with the Atom Syndication Format [RFC4287]. Moreover, they MUST adhere to the semantic mapping between the ORE Model and the Atom model detailed Section 2, as well as to the restrictions and extensions for Atom representations of Resource Maps detailed in Section 3 and Section 4.

Specifically, an Atom representation of a Resource Map MUST be a well-formed XML document that is valid according to the Relax NG Compact Schema of [RFC4287]. Moreover, it MUST be valid according to the more specific Schematron Schema of Appendix C that further restricts the Atom syntax to represent Resource Maps.

1.4 Example

Throughout the remainder of this document, the following scenario will be used to illustrate the specifics of Atom-based representations of Resource Maps.

<?xml version="1.0" encoding="UTF-8" ?>
<atom:feed  xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:ore="http://www.openarchives.org/ore/terms/"
    xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
    grddl:transformation="http://www.openarchives.org/ore/atom/atom-grddl.xsl"> 

    <!-- About the Aggregation --> 

    <atom:id>http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
    <atom:author>
        <atom:name>Michael Nelson</atom:name>
        <atom:uri>http://www.cs.odu.edu/~mln/</atom:uri>
    </atom:author>
    <atom:author>
        <atom:name>Joan Smith</atom:name>
        <atom:uri>http://www.joanasmith.com/</atom:uri>
    </atom:author>
    <atom:author>
        <atom:name>Frank McCown</atom:name>
        <atom:uri>http://www.cs.odu.edu/~fmccown/</atom:uri>
    </atom:author>
    <atom:title>Observed Web Robot Behavior on Decaying Web Subsites</atom:title>
    <atom:link href="info:doi/10.1045/february2006-smith" 
        rel="related"/>
    <atom:category  scheme="http://www.openarchives.org/ore/terms/" 
        term="http://www.openarchives.org/ore/terms/Aggregation" 
        label="Aggregation" />
    <atom:category  scheme="http://purl.org/eprint/type/" 
        term="http://purl.org/eprint/type/JournalArticle" 
        label="Journal Article" />
    <atom:link rel="alternate" 
        type="application/rdf+xml" 
        href="http://www.dlib.org/dlib/february06/smith/aggregation.rdf" />

    <!-- About the Resource Map --> 

    <atom:link rel="self" 
        type="application/atom+xml" 
        href="http://www.dlib.org/dlib/february06/smith/aggregation.atom" />
    <atom:generator uri="http://www.dlib.org">D-Lib Magazine</atom:generator>
    <atom:updated>2007-09-22T07:11:09Z</atom:updated>

    <!-- Aggregated Resources --> 

    <atom:entry>
        <atom:id>http://oreproxy.org/r?what=http://www.dlib.org/dlib/february06/smith/02smith.html&amp;where=http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
        <atom:author>
            <atom:name>Michael Nelson</atom:name>
            <atom:uri>http://www.cs.odu.edu/~mln/</atom:uri>
        </atom:author>
        <atom:author>
            <atom:name>Joan Smith</atom:name>
            <atom:uri>http://www.joanasmith.com/</atom:uri>
        </atom:author>
        <atom:author>
            <atom:name>Frank McCown</atom:name>
            <atom:uri>http://www.cs.odu.edu/~fmccown/</atom:uri>
        </atom:author>
        <atom:title>Observed Web Robot Behavior on Decaying Web Subsites</atom:title>
        <atom:updated>2007-08-17T21:12:44Z</atom:updated>
        <atom:category scheme="http://purl.org/ontology/bibo/" 
            term="http://purl.org/ontology/bibo/WebPage" 
            label="WebPage" />
        <atom:category  scheme="http://purl.org/dc/dcmitype/" 
            term="http://purl.org/dc/dcmitype/Text" 
            label="Text" />
        <atom:category  scheme="info:eu-repo/semantics/" 
            term="info:eu-repo/semantics/humanStartPage" 
            label="Human Start Page" />        
        <atom:link  rel="alternate" type="text/html" 
            href="http://www.dlib.org/dlib/february06/smith/02smith.html" />
    </atom:entry>
    <atom:entry>
        <atom:id>http://oreproxy.org/r?what=http://www.dlib.org/dlib/february06/smith/pg1-13.html&amp;where=http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
        <atom:title>owenbrauODULPT2 dgrp1 pg1-13-html</atom:title>
        <atom:updated>2007-08-17T21:12:44Z</atom:updated>
        <atom:category scheme="http://purl.org/ontology/bibo/" 
            term="http://purl.org/ontology/bibo/WebPage" 
            label="WebPage" />
        <atom:category  scheme="http://purl.org/dc/dcmitype/" 
            term="http://purl.org/dc/dcmitype/Text" 
            label="Text" />
        <atom:link  rel="alternate" 
            type="text/html" 
            href="http://www.dlib.org/dlib/february06/smith/pg1-13.html" />
    </atom:entry>
    <atom:entry>
        <atom:id>http://oreproxy.org/r?where=what=http://www.dlib.org/dlib/february06/smith/pg1-13.pdf&amp;http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
        <atom:title>owenbrauODULPT2 dgrp1 pg1-13-pdf</atom:title>
        <atom:updated>2007-08-17T21:12:44Z</atom:updated>
        <atom:category  scheme="http://purl.org/dc/dcmitype/" 
            term="http://purl.org/dc/dcmitype/Text" 
            label="Text" />
        <atom:link  rel="alternate" 
            type="application/pdf" 
            href="http://www.dlib.org/dlib/february06/smith/pg1-13.pdf" />
    </atom:entry>
    <atom:entry>
        <atom:id>http://oreproxy.org/r?what=http://www.dlib.org/dlib/february06/smith/MLN_Google.png&amp;where=http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
        <atom:title>MLN_Google.png</atom:title>
        <atom:updated>2007-09-22T07:11:09Z</atom:updated>
        <atom:category  scheme="http://purl.org/dc/dcmitype/" 
            term="http://purl.org/dc/dcmitype/Image" 
            label="Image" />
        <atom:link  rel="alternate" 
            type="image/png" 
            href="http://www.dlib.org/dlib/february06/smith/MLN_Google.png" />
    </atom:entry>
    <atom:entry>
        <atom:id>http://oreproxy.org/r?what=http://www.crossref.org/openurl?url_ver=Z39.88-2004%26rft_id=info:doi/10.1045/february2006-smith%26noredirect=true&amp;where=http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
        <atom:author>
            <atom:name>CrossRef</atom:name>
            <atom:uri>http://www.crossref.org</atom:uri>
        </atom:author>
        <atom:title>Bibliographic metadata for info:doi/10.1045/february2006-smith</atom:title>
        <atom:updated>2007-08-17T21:12:44Z</atom:updated>
        <atom:category  scheme="info:eu-repo/semantics/" 
            term="info:eu-repo/semantics/descriptiveMetadata" 
            label="Descriptive Metadata" />  
        <atom:link rel="alternate" 
            type="application/xml" 
            href="http://www.crossref.org/openurl?url_ver=Z39.88-2004&amp;rft_id=info:doi/10.1045/february2006-smith&amp;noredirect=true" />
    </atom:entry>
</atom:feed>

2. Correspondence between the ORE Model and the Atom Model

2.1. Mapping between the ORE Model and the Atom Model: Basics

Table 1, Figure 1 and Figure 2 illustrate how entities from the ORE Model map to entities from the Atom model [RFC4287].

In general, the mapping leverages the fact that the Atom model distinguishes between two URIs that pertain to an Atom Feed:

• The URI of the Atom Feed itself, which corresponds to the URI of an Aggregation (URI-A) of the ORE Model, and
• The URI from which an Atom Feed Document is retrievable, which corresponds with the URI of a Resource Map (URI-R) that describes an Aggregation, and from which a representation is available that serializes the Resource Map according to a specific format (Atom in this case).

The mapping also introduces an Atom Entry for each Aggregated Resource of the Aggregation. Two URIs introduced by the ORE Model in relation to an Aggregated Resource are expressed in Atom in the following way:

• The URI of the Aggregated Resource (URI-AR) itself is conveyed in the Atom Entry as the link target of a unique atom:link child element of atom:entry that expresses an "alternate" relationship; this URI is the value of the href attribute of this atom:link.
• The URI of the Proxy for an Aggregated Resource (URI-P), which is introduced as an optional concept by the ORE Model, corresponds with the identifier of the Atom Entry that conveys the Aggregated Resource. This URI denotes the Aggregated Resource not in its own right, but rather as it exists in the context of the Aggregation. The URI of the Proxy for the Aggregated Resource is the value of the atom:id child element of the atom:entry. Since atom:id are mandatory in Atom, the use of Proxy URIs in the Resource Map Profile of Atom is not optional but REQUIRED.

Furthermore, the mapping introduces an unambiguous way to interpret other elements provided in an Atom-based Resource Map in terms of the ORE Model:

• For child elements of atom:feed this mapping between Atom and ORE is detailed in Table 2. In summary:
  • The atom:generator, atom:updated, and atom:rights child elements of atom:feed pertain to the Resource Map, and correspond with the dcterms:creator, dcterms:modified and dc:rights elements introduced in the ORE Model as Metadata pertaining to a Resource Map;
  • All other child elements of atom:feed that are in the Atom namespace pertain to the Aggregation described by the Resource Map;
  • The content of an rdf:Description child element of atom:feed pertains to either the Aggregation or the Resource Map, depending on the URI (URI-A or URI-R) that is provided as the value of the rdf:about attribute of the element;
  • The content of additional rdf:Description child elements of atom:feed pertain to the resource for which the URI is provided as the value of the rdf:about attribute of the element and are used to express types and relationships of resources that have a direct or indirect relationsip to the Aggregation or the Resource Map;
  • Other child elements of atom:feed have no correspondence in the ORE Model, and MAY be ignored by ORE processors.
• For child elements of atom:entry this mapping between Atom and ORE is detailed in Table 3 . In summary:
  • The atom:published, atom:updated, atom:rights and atom:source child elements of atom:entry are Atom-specific metadata. They pertain to the Atom Entry and have no correspondence in the ORE Model;
  • An atom:link child element of atom:entry that has a rel attribute with a value of "via" may be used to express the notion of Lineage introduced in the ORE Model. It pertains to the Proxy of the Aggregated Resource conveyed by the Atom Entry;
  • All other child elements of atom:entry that are in the Atom namespace pertain to the Aggregated Resource conveyed in the Atom Entry;
  • The content of an rdf:Description child element of atom:entry pertains to either the Aggreged Resource or to its Proxy, depending on the URI (URI-AR or URI-P) that is provided as the value of the rdf:about attribute of the element;
  • The content of additional rdf:Description child elements of atom:entry pertain to the resource for which the URI is provided as the value of the rdf:about attribute of the element and are used to express types and relationships of resources that have a direct or indirect relationsip to the Aggregated Resource or to its Proxy;
  • Other child elements of atom:entry have no correspondence in the ORE Model, and MAY be ignored by ORE processors.

Figure 1: Mapping between basic items from the ORE and Atom models

Figure 2: Mapping between advanced items from the ORE and Atom models

2.2. Mapping between the ORE Model and the Atom Model: Atom Elements and RDF Triples

Table 2 shows the elements of an Atom Feed used to serialize a Resource Map in the Atom format. Elements that are mandatory are highlighted. Note that the column "ORE Abstract Model, and RDF Triples" of this table indicates how elements of an Atom-based Resource Map SHOULD be mapped to RDF triples. As shown, some predicates for these RDF triples are in the ore namespace, while others are in other, commonly used namespaces listed in Section 1.2.

Table 3 shows the elements of an Atom Entry used to serialize a Resource Map in the Atom format. Elements that are mandatory are highlighted. Note that the column "ORE Abstract Model, and RDF Triples" of this table indicates how elements of an Atom-based Resource Map SHOULD be mapped to RDF triples. As shown, some predicates for these RDF triples are in the ore namespace, while others are in other, commonly used namespaces listed in Section 1.2.

3. Use of Atom Constructs in the Resource Map Profile of Atom

This Section specifies the use of common Atom Constructs to represent Resource Maps in Atom. When, in the remainder of this document, an Atom element is identified as being a particular kind of construct, it inherits the requirements specified here.

3.1 Text Constructs

In the Resource Map Profile of Atom:

• The Text construct MUST be used in a manner described in the Text Construct section of [RFC4287].

3.2 Person Constructs

In the Resource Map Profile of Atom:

• The Person construct MUST be used in a manner described in the Person Construct section of [RFC4287].

3.3 Date Constructs

In the Resource Map Profile of Atom:

• The Date construct MUST be used in a manner described in the Date Construct section of [RFC4287].
• In the Resource Map Profile of Atom, expressing date-times in UTC is RECOMMENDED. The use of the special UTC designator ("Z") is RECOMMENDED over the notation using a numeric time zone offset. Hence, the RECOMMENDED format is YYYY-MM-DDThh:mm:ssZ.

4. Use of Atom Elements in the Resource Map Profile of Atom

4.1 Container Elements

4.1.1 The "atom:feed" Element

In the Resource Map Profile of Atom:

• The "atom:feed" element has semantics and properties as described in the atom:feed Element section of [RFC4287] unless specified differently below.
• An Atom Feed corresponds with an Aggregation of the ORE Model, and an Atom Feed Document corresponds with the (Atom-based) Resource Map of the ORE Model.
• The following rules apply regarding child elements of the atom:feed element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:feed elements MAY contain any number atom:author elements.
    • The atom:author element SHOULD convey meaningful authorship information for the Aggregation.
    • The use of a URI to identify an author is RECOMMENDED.
  • atom:feed elements MUST contain exactly one atom:category element typing the Atom Feed as an Aggregation.
    • This element MUST have a scheme attribute value of "http://www.openarchives.org/ore/terms/", a term attribute value of "http://www.openarchives.org/ore/terms/Aggregation", and a label attribute value of "Aggregation".
  • atom:feed elements MAY contain any number of atom:category elements in addition to the aforementioned one.
    • The atom:category element MUST convey a categorization or semantic type information for the Aggregation; It corresponds with the rdf:type relationship of the ORE Model.
  • atom:feed elements MAY contain any number of atom:contributor elements.
    • The atom:contributor element SHOULD convey meaningful contributor information for the Aggregation.
    • The use of a URI to identify a contributor is RECOMMENDED.
  • atom:feed elements MUST contain one or more atom:entry elements.
    • Each atom:entry element MUST convey an Aggregated Resource of the Aggregation.
  • atom:feed elements MUST contain exactly one atom:generator element.
    • The atom:generator element MUST convey the author of the Atom-based Resource Map; it corresponds with the dcterms:creator element introduced in the ORE Model as Metadata pertaining to a Resource Map.
    • The uri attribute of this atom:generator element is REQUIRED, and MUST convey a URI associated with the author of the Atom-based Resource Map.
  • atom:feed elements MUST NOT contain more than one atom:icon element.
    • The atom:icon element conveys an icon for the Aggregation.
  • atom:feed elements MUST contain exactly one atom:id element.
    • The atom:id element MUST convey the URI of the Aggregation (URI-A) of the ORE Model.
    • Guidelines on minting URIs for Aggregations are provided in the ORE User Guide - HTTP Implementation and Multiple Serializations.
  • atom:feed elements MUST contain one atom:link element with a rel attribute value of "self".
    • The href attribute value of this atom:link element MUST be the URI of the (Atom-based) Resource Map (URI-R) of the ORE Model.
    • The type attribute value of this atom:link element SHOULD be "application/atom+xml".
  • atom:feed elements MAY contain any number of atom:link elements with a rel attribute value of "related".
    • The href attribute value of this atom:link element MUST be a URI of a resource that is similar to the Aggregation described by the Resource Map. It corresponds with the ore:similarTo relationship of the ORE Model.
  • atom:feed elements MAY contain any number of atom:link elements with a rel attribute value of "alternate".
    • The href attribute value of this atom:link element MUST be the URI of another Resource Map that describes the same Aggregation as the one described by the current Atom-based Resource Map, i.e. the linked Resource Map and the current Resource Map MUST have the same URI-A. This atom:link corresponds with the ore:isDescribedBy relationship introduced in the ORE Model.
    • The type attribute value of this link SHOULD convey the media type of the other Resource Map.
  • atom:feed elements MUST NOT contain more than one atom:link element with a rel attribute value of "license".
    • The href attribute value of this atom:link element MUST be the URI of a rights expression pertaining to the Aggregation.
    • It is RECOMMENDED that the referenced rights expression is machine readable.
  • atom:feed elements MAY contain additional atom:link elements beyond those described above.
    • These atom:link elements have no correspondence in the ORE Model, and MAY be ignored by ORE processors.
  • atom:feed elements MUST NOT contain more than one atom:link element with a rel attribute value of "alternate" that has the same combination of type and hreflang attribute values.
  • atom:feed elements MUST NOT contain more than one atom:logo element.
    • The atom:logo element conveys a logo for the Aggregation.
    • The atom:logo element has no correspondence in the ORE Model, and MAY be ignored by ORE processors.
  • atom:feed elements MUST NOT contain more than one atom:rights element.
    • The atom:rights element SHOULD NOT be used to convey machine-readable licensing information.
    • The atom:rights element MUST convey the rights pertaining to the Resource Map; it corresponds with the dc:rights element introduced in the ORE Model as Metadata pertaining to a Resource Map.
  • atom:feed elements MUST NOT contain more than one atom:subtitle element.
    • The atom:subtitle element SHOULD convey a meaningful subtitle for the Aggregation.
  • atom:feed elements MUST contain exactly one atom:title element.
    • The atom:title element SHOULD convey a meaningful title for the Aggregation.
  • atom:feed elements MUST contain exactly one atom:updated element.
    • The atom:updated element MUST convey the date-time of most recent update of the Atom-based Resource Map; it corresponds with the dcterms:modified element introduced in the ORE Model as Metadata pertaining to a Resource Map.
  • atom:feed elements SHOULD NOT contain more than one rdf:Description element with a value of its rdf:about attribute equal to the URI of the Aggregation (URI-A).
    • This element MUST be used to convey types and relationships pertaining to the Aggregation that can not be expressed using child elements of atom:feed that are in the Atom namespace.
  • atom:feed elements SHOULD NOT contain more than one rdf:Description element with a value of its rdf:about attribute equal to the URI of the Atom-based Resource Map (URI-R).
    • This element MUST be used to convey types and relationships pertaining to the Atom-based Resource Map that can not be expressed using child elements of atom:feed that are in the Atom namespace.
  • atom:feed elements MAY contain any number of rdf:Description elements with a value of their rdf:about attribute equal to a URI other than the URI of the Aggregation (URI-A) or the Atom-based Resource Map (URI-R).
    • Such elements MAY be used to convey types and relationships pertaining to resources other than the Aggregated Resources that have a direct or indirect relationships with the Aggregation or the Resource Map.
  • Child elements of atom:feed other than the ones listed above have no correspondence in the ORE Model, and MAY be ignored by ORE processors.
  • An Atom Feed Document MUST NOT have multiple atom:entry elements with the same atom:id value, as is permitted by [RFC4287]. Such entries would convey the same Aggregated Resource, and might contain conflicting assertions about that Aggregated Resource within the confines of the same Resource Map. As a result, updating an atom:entry in the Resource Map Profile of Atom MUST always be achieved by editing the existing atom:entry and by changing the value of its atom:updated child element. It MUST NOT be achieved by adding an additional atom:entry with the same atom:id as the already existing one.

4.1.2 The "atom:entry" Element

In the Resource Map Profile of Atom:

• The "atom:entry" element has semantics and properties as described in the atom:entry Element section of [RFC4287] unless specified differently below.
• An Atom entry conveys an Aggregated Resource, Types and Relationships pertaining to the Aggregated Resource, as well as some Atom-specific information.
• The following rules apply regarding child elements of the atom:entry element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:entry elements MAY contain any number of atom:author elements.
    • The atom:author element SHOULD convey a meaningful author for the Aggregated Resource.
    • The use of a URI to identify an author is RECOMMENDED.
    • If the author of the Aggregated Resource is considered to be anonymous or otherwise unknown, an atom:author element containing nothing except an empty atom:name child element MUST be provided.
    • If no atom:author element is provided, then the atom:author elements of the contained atom:source element are considered to apply.
    • If none of these atom:author elements exist, then the atom:author elements of the atom:feed element are considered to apply.
  • atom:entry elements MUST NOT contain more than one atom:category element that types the Aggregated Resource as an Aggregation. Typing an Aggregated Resource in this manner corresponds with the notion of Nesting Aggregations introduced in the ORE Model.
    • This element MUST have a scheme attribute value of "http://www.openarchives.org/ore/terms/", a term attribute value of "http://www.openarchives.org/ore/terms/Aggregation", and SHOULD have a label attribute value of "Aggregation".
  • atom:entry elements MAY contain any number of additional atom:category elements.
    • The atom:category element MUST convey a categorization or semantic type information for the Aggregated Resource; It corresponds with the rdf:type relationship of the ORE Model.
  • atom:entry elements MUST NOT contain any atom:content elements.
  • atom:entry elements MAY contain any number of atom:contributor elements.
    • The atom:contributor element SHOULD convey meaningful contributor information for the Aggregated Resource.
    • The use of a URI to identify a contributor is RECOMMENDED.
  • atom:entry elements MUST contain exactly one atom:id element.
    • The atom:id element MUST convey the URI of the Proxy for the Aggregated Resource (URI-P) as introduced in the ORE Model.
    • Guidelines on minting URIs for Proxies are provided in the ORE User Guide - HTTP Implementation and Mutliple Serializations.
  • atom:entry elements MUST contain one atom:link element with a rel attribute value of "alternate".
    • The href attribute value of this atom:link element MUST be the URI of the Aggregated Resource (URI-AR).
  • atom:entry elements MAY contain any number of atom:link elements with a rel attribute value of "related".
    • The href attribute value of this atom:link element MUST be the URI of another Aggregation in which the Aggregated Resource is aggregated. It corresponds to the ore:isAggregatedBy relationship introduced in the ORE Model.
    • The type and length attributes of this atom:link SHOULD NOT be used as Aggregations are non-information resources; they have no mime type nor lenght.
  • atom:entry elements MUST NOT contain more than one atom:link element with a rel attribute value of "self".
    • This is the (optional) preferred URI for retrieving Atom Entry Documents representing this Atom entry.
    • The type attribute value of this atom:link element SHOULD be "application/atom+xml".
    • The href attribute value of this atom:link element MUST NOT be the URI of the Aggregated Resource (URI-AR).
    • This atom:link element has no correspondence in the ORE Model, and MAY be ignored by ORE processors.
  • atom:entry elements MAY contain any number of atom:link elements with a rel attribute value of "via".
    • This link MUST be used to express the lineage of the Aggregated Resource in another Aggregation as introduced in the ORE Model.
    • The href attribute value of this atom:link element MUST be the URI of a Proxy for the Aggregated Resource in another Aggregation.
  • atom:entry elements MUST NOT contain any atom:link elements other than the aformentioned ones.
  • atom:entry elements MUST NOT contain more than one atom:published element.
    • The atom:published element SHOULD convey the date-time of creation of the atom:entry element that conveys the Aggregated Resource. In the ORE perspective, it corresponds with the date-time the Aggregated Resource was first aggregated in the Aggregation.
  • atom:entry elements MUST NOT contain more than one atom:rights elements.
    • The atom:rights element SHOULD NOT be used to convey machine-readable licensing information.
    • The atom:rights element MUST convey the rights pertaining to the atom:entry;
    • If no atom:rights element is provided, then the atom:rights of the atom:feed element are considered to apply.
  • atom:entry elements MUST NOT contain more than one atom:source element.
    • The atom:source element MUST convey the origin of the atom:entry in another Atom Feed Document;
    • The atom:source element has no correspondence in the ORE Model.
  • atom:entry elements MUST NOT contain more than one atom:summary element.
    • The atom:summary element SHOULD convey meaningful summary for the Aggregated Resource.
  • atom:entry elements MUST contain exactly one atom:title element.
    • The atom:title element SHOULD convey a meaningful title for the Aggregated Resource.
  • atom:entry elements MUST contain exactly one atom:updated element.
    • The atom:updated element SHOULD convey the date-time of most recent update of the atom:entry.
  • atom:entry elements SHOULD NOT contain more than one rdf:Description element with a value of its rdf:about attribute equal to the URI of the Aggregated Resource (URI-AR).
    • This element MUST be used to convey types and relationships pertaining to the Aggregated Resource that can not be expressed using child elements of atom:entry that are in the Atom namespace.
  • atom:entry elements SHOULD NOT contain more than one rdf:Description element with a value of its rdf:about attribute equal to the URI of the Proxy for the Aggregated Resource (URI-P).
    • This element MUST be used to convey types and relationships pertaining to the Proxy for the Aggregated Resource.
  • atom:entry elements MAY contain any number of rdf:Description elements with a value of their rdf:about attribute equal to a URI other than the URI of the Aggregated Resource (URI-AR) or of its Proxy (URI-P).
    • Such elements MAY be used to convey types and relationships pertaining to resources (other than the Aggregation and the Resource Map) that have a direct or indirect relationships with the Aggregated Resource.
  • Child elements of atom:entry other than the ones listed above have no correspondence in the ORE Model, and MAY be ignored by ORE processors.

4.1.3 The "atom:content" Element

In the Resource Map Profile of Atom:

• The "atom:content" element MUST NOT be used.

4.2 Metadata Elements

4.2.1 The "atom:author" Element

In the Resource Map Profile of Atom:

• The "atom:author" element has semantics and properties as described in the atom:author Element section of [RFC4287] unless specified differently below.
• The "atom:author" element is a Person construct that indicates the author of an Atom Feed or Atom Entry.
• The following rules apply regarding the atom:author element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:feed elements MAY contain any number of atom:author elements.
    • The atom:author element SHOULD convey meaningful authorship information for the Aggregation.
    • The use of a URI to identify an author is RECOMMENDED.
  • atom:entry elements MAY contain any number of atom:author elements.
    • The atom:author element SHOULD convey a meaningful author for the Aggregated Resource.
    • The use of a URI to identify an author is RECOMMENDED.
    • If the author of the Aggregated Resource is considered to be anonymous or otherwise unknown, an atom:author element containing nothing except an empty atom:name child element MUST be provided.
    • If no atom:author element is provided, then the atom:author elements of the contained atom:source element are considered to apply.
    • If none of these atom:author elements exist, then the atom:author elements of the atom:feed element are considered to apply.

<?xml version="1.0" encoding="UTF-8" ?>
<atom:feed  xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:ore="http://www.openarchives.org/ore/terms/"> 

    <!-- About the Aggregation --> 

    <atom:author>
        <atom:name>Michael Nelson</atom:name>
        <atom:uri>http://www.cs.odu.edu/~mln/</atom:uri>
    </atom:author>
    <atom:author>
        <atom:name>Joan Smith</atom:name>
        <atom:uri>http://www.joanasmith.com/</atom:uri>
    </atom:author>
    <atom:author>
        <atom:name>Frank McCown</atom:name>
        <atom:uri>http://www.cs.odu.edu/~fmccown/</atom:uri>
    </atom:author>

    <!-- Aggregated Resources --> 

    <atom:entry>
        <!-- Authorship of Aggregated Resource inherited from Feed-level author -->
        <atom:link  rel="alternate" 
            type="application/pdf" 
            href="http://www.dlib.org/dlib/february06/smith/pg1-13.pdf" />
    </atom:entry>
    <atom:entry>
        <!-- Authorship of Aggregated Resource unknown or anonymous --> 
        <!-- Authorship not inherited from Feed-level author -->
        <atom:author>
            <atom:name/>
        </atom:author>
        <atom:link  rel="alternate" 
            type="image/png" 
            href="http://www.dlib.org/dlib/february06/smith/MLN_Google.png" />
    </atom:entry>
    <atom:entry>
        <!-- Authorship of Aggregated Resource is known and different from Feed-level author --> 
        <!-- Authorship not inherited from Feed-level author -->
        <atom:author>
            <atom:name>CrossRef</atom:name>
            <atom:uri>http://www.crossref.org</atom:uri>
        </atom:author>
        <atom:link rel="alternate" 
            type="application/xml" 
            href="http://www.crossref.org/openurl?url_ver=Z39.88-2004&amp;rft_id=info:doi/10.1045/february2006-smith&amp;noredirect=true" />
    </atom:entry>
</atom:feed>

4.2.2 The "atom:category" Element

In the Resource Map Profile of Atom:

• The "atom:category" element has semantics and properties as described in the atom:category Element section of [RFC4287] unless specified differently below.
• The "atom:category" element conveys types pertaining to an Atom Feed or an Atom Entry.
• The following rules apply regarding the atom:category element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:feed elements MUST contain exactly one atom:category element typing the Atom Feed as an Aggregation.
    • This element MUST have a scheme attribute value of "http://www.openarchives.org/ore/terms/", a term attribute value of "http://www.openarchives.org/ore/terms/Aggregation", and SHOULD have a label attribute value of "Aggregation".
  • atom:feed elements MAY contain any number of atom:category elements in addition to the aforementioned one.
    • The atom:category element MUST convey a categorization or semantic type information for the Aggregation; It corresponds with the rdf:type relationship of the ORE Model.
  • atom:entry elements MUST NOT contain more than one atom:category element that types the Aggregated Resource as an Aggregation. Typing an Aggregated Resource in this manner corresponds with the notion of Nesting Aggregations introduced in the ORE Model.
    • This element MUST have a scheme attribute value of "http://www.openarchives.org/ore/terms/", a term attribute value of "http://www.openarchives.org/ore/terms/Aggregation", and SHOULD have a label attribute value of "Aggregation".
  • atom:entry elements MAY contain any number of additional atom:category elements.
    • The atom:category element MUST convey a categorization or semantic type information for the Aggregated Resource; It corresponds with the rdf:type relationship of the ORE Model.

<?xml version="1.0" encoding="UTF-8" ?>
<atom:feed  xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:ore="http://www.openarchives.org/ore/terms/"> 

    <!-- About the Aggregation --> 

    <atom:category  scheme="http://www.openarchives.org/ore/terms/" 
        term="http://www.openarchives.org/ore/terms/Aggregation" 
        label="Aggregation" />
    <atom:category  scheme="http://purl.org/eprint/type/" 
        term="http://purl.org/eprint/type/JournalArticle" 
        label="Journal Article" />

</atom:feed>

4.2.3 The "atom:contributor" Element

In the Resource Map Profile of Atom:

• The "atom:contributor" element has semantics and properties as described in the atom:contributor Element section of [RFC4287] unless specified differently below.
• The "atom:contributor" element is a Person construct that indicates a person or other entity who contributed to an Atom Feed or an Atom Entry.
• The following rules apply regarding the atom:contributor element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • The atom:contributor element SHOULD convey meaningful contributor information pertaining to the Aggregation or the Aggregated Resource.
  • The use of a URI to identify a contributor is RECOMMENDED.
  • atom:feed elements MAY contain any number of atom:contributor elements.
  • atom:entry elements MAY contain any number of atom:contributor elements.

4.2.4 The "atom:generator" Element

In the Resource Map Profile of Atom:

• The "atom:generator" element has semantics and properties as described in the atom:generator Element section of [RFC4287] unless specified differently below.
• The following rules apply regarding the atom:generator element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:feed elements MUST contain exactly one atom:generator element.
  • The atom:generator element MUST convey the author of the Resource Map; it corresponds with the dcterms:creator element introduced in the ORE Model as Metadata pertaining to a Resource Map.
  • The uri attribute of this atom:generator element is REQUIRED, and MUST convey a URI associated with the author of the Atom-based Resource Map.

<?xml version="1.0" encoding="UTF-8" ?>
<atom:feed  xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:ore="http://www.openarchives.org/ore/terms/"> 

    <!-- About the Resource Map --> 

    <atom:generator uri="http://www.dlib.org">D-Lib Magazine</atom:generator>

</atom:feed>

4.2.5 The "atom:icon" Element

In the Resource Map Profile of Atom:

• The "atom:icon" element has semantics and properties as described in the atom:icon Element section of [RFC4287] unless specified differently below.
• The "atom:icon" is an IRI reference [RFC3987] that identifies an image that provides iconic visual identification for a Resource Map (Atom feed).
• The following rules apply regarding the atom:icon element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:feed elements MUST NOT contain more than one atom:icon element.
  • The atom:icon element conveys an icon for the Aggregation.

<?xml version="1.0" encoding="UTF-8" ?>
<atom:feed  xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:ore="http://www.openarchives.org/ore/terms/"> 

    <!-- About the Aggregation --> 

    <atom:icon>http://www.dlib.org/icon/dlib_icon.png</atom:icon>

</atom:feed>

4.2.6 The "atom:id" Element

In the Resource Map Profile of Atom:

• The "atom:id" element has semantics and properties as described in the atom:id Element section of [RFC4287] unless specified differently below.
• The "atom:id" element conveys a permanent, universally unique identifier for an Atom feed or Atom entry.
• The normalization guidelines for generating atom:id elements are as described in the atom:id Element section of [RFC4287].
• The rules for comparing atom:id are as expressed in the Comparing atom:id section of [RFC4287].
• The following rules apply regarding the atom:id element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • The content of the atom:id element MUST be a IRI reference [RFC3987].
  • atom:feed elements MUST contain exactly one atom:id element.
    • The atom:id element MUST convey the URI of the Aggregation (URI-A) of the ORE Model.
    • Guidelines on minting URIs for Aggregations are provided in the ORE User Guide - HTTP Implementation and Multiple Serializations.
  • atom:entry elements MUST contain exactly one atom:id element.
    • The atom:id element MUST convey the URI of the Proxy for the Aggregated Resource (URI-P) as introduced in the ORE Model.
    • Guidelines on minting URIs for Proxies are provided in the ORE User Guide - HTTP Implementation and Mutliple Serializations.

<?xml version="1.0" encoding="UTF-8" ?>
<atom:feed  xmlns:atom="http://www.w3.org/2005/Atom"
    xmlns:ore="http://www.openarchives.org/ore/terms/"> 

    <!-- About the Aggregation --> 

    <atom:id>http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>

    <!-- About the Resource Map  --> 

    <atom:link rel="self" 
        type="application/atom+xml" 
        href="http://www.dlib.org/dlib/february06/smith/aggregation.atom" />

    <!-- Aggregated Resource --> 

    <atom:entry>
        <atom:id>http://oreproxy.org/r?what=http://www.dlib.org/dlib/february06/smith/02smith.html&amp;where=http://www.dlib.org/dlib/february06/smith/aggregation</atom:id>
        <atom:link  rel="alternate" type="text/html" 
            href="http://www.dlib.org/dlib/february06/smith/02smith.html" />
    </atom:entry>

</atom:feed>

4.2.7 The "atom:link" Element

In the Resource Map Profile of Atom:

• The "atom:link" element has semantics and properties as described in the atom:link Element section of [RFC4287] unless specified differently below.
• The atom:link element has attributes as described in the sections The "href" Attribute, The "rel" Attribute, The "type" Attribute, The "hreflang" Attribute, The "title" Attribute and The "length" Attribute of [RFC4287].
• The following rules apply regarding the atom:link element; rules that are more specific than the ones of [RFC4287] are shown in italic:
  • atom:feed elements MUST contain one atom:link element with a rel attribute value of "self".
    • The type attribute value of this atom:link element SHOULD be "application/atom+xml".
    • The href attribute value of this atom:link element MUST be the URI of the Atom-based Resource Map (URI-R) of the ORE Model.
  • atom:feed elements MAY contain any number of atom:link elements with a rel attribute value of "related".
    • The href attribute value of this atom:link element MUST be a URI of a resource that is similar to the Aggregation described by the Resource Map. It corresponds with the ore:similarTo relationship of the ORE Model.
  • atom:feed elements MAY contain any number of atom:link elements with a rel attribute value of "alternate".
    • The href attribute value of this atom:link element MUST be the URI of another Resource Map that describes the same Aggregation as the one described by the current Atom-based Resource Map, i.e. the linked Resource Map and the current Resource Map MUST have the same URI-A. This atom:link corresponds with the ore:isDescribedBy relationship introduced in the ORE Model.
    • The type attribute value of this link SHOULD convey the media type of the other Resource Map.
  • atom:feed elements MUST NOT contain more than one atom:link element with a rel attribute value of "license".
    • The href attribute value of this atom:link element MUST be the URI of a rights expression pertaining to the Aggregation.
    • It is RECOMMENDED that the referenced rights expression is machine readable.