ORE User Guide - Resource Map Implementation in Atom

Abstract

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 resource that is a specialization of a named graph. 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. Although multiple serializations of Resource Maps are possible, the initial serialization is done using the Atom Syndication Format [RFC4287]. A detailed examination of the mapping of ORE Data Model concepts to the Atom Syndication Format is known as the Resource Map Profile of Atom [ReMProfileofAtom]. The purpose of this document is to provide guidance to application developers on how to implement and interpret the Resource Map Profile of Atom. This user guide is one of several documents comprising the OAI-ORE specification and user guide.

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 resource that is a specialization of a named graph. 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. Although multiple serializations of Resource Maps are possible, the initial serialization is done using the Atom Syndication Format [RFC4287]. A detailed examination of the mapping of ORE Data Model concepts to the Atom Syndication Format is known as the Resource Map Profile of Atom [ReMProfileofAtom]. The purpose of this document is to provide guidance to application developers on how to implement and interpret the Resource Map Profile of Atom. We anticipate that the contents and guidance given in this document to evolve over time to reflect the best practices of the community.

This document does not address ReM validation. Readers interested in validation are referred to Appendix C of [ReMProfileofAtom] for a Schematron Schema of the Resource Map Profile of Atom.

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 RFC 2119 [IETF RFC 2119].

2. Populating Elements

The Atom Syndication Format defines many elements and the Resource Map Profile of Atom [ReMProfileofAtom] defines which elements have special meaning when a ReM is serialized as an Atom feed. In this section, the most common and potentially confusing elements are examined and best practices are put forward regarding their population. Throughout document, we will use the following arXiv e-print as the defining example:

http://arxiv.org/abs/astro-ph/0601007

This is an interesting example because it has multiple identifiers, versions, formats, mirrors and external relationships. Although arXiv does not yet support ReMs, we will assume in the examples below a hypothetical ReM available at the following URI ("URI-R" from [ORE Model]):

http://arxiv.org/rem/astro-ph/0601007

The subsections below provide a step-by-step build-up of a ReM for the above arXiv e-print, culminating in a minimal but complete ReM that later sections will further expand.

2.1 Creating the Skeleton of a ReM

We begin by creating the skeleton of a ReM and Aggregation, highlighting the values of the elements that map to the ORE Data Model and the conventions that declare that an Atom Feed that is being used to represent an ORE aggregation (see Table 1 of [ReMProfileofAtom] for a complete mapping of the ORE and Atom models).

The values of URI-A and URI-R (as defined in [ORE Model]) are used to populated /feed/id and /feed/link[@rel="self"]/@href, respectively. There are multiple methods for choosing values for URI-A and URI-R (see [ORE HTTP] for further information). In this example, we use the simple method of "URI-A = URI-R#aggregation".
Next, we give values to the ReM-specific elements, /feed/generator and /feed/updated. For /feed/generator, we use the author(s) of the ReM. This value is often different from the authors of the Aggregation (see the metadata section below). In this example, the ReM author is "arXiv.org e-Print Repository" and the Aggregation authors are "Hui Li, Zong-Kuan Guo, Yuan-Zhong Zhang". The value of /feed/updated is the datetime of the last update to the ReM (in this case, the creation time of the ReM). It is NOT the date of publication of the Aggregation.
Finally, we use a /feed/category element to designate that we have an ORE aggregation in the ReM.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />

</feed>

2.2 Adding Aggregated Resources

In the ORE Model, /feed/entry elements correspond to Aggregated Resources (again, see Table 1 of [ReMProfileofAtom] for a complete mapping of the ORE and Atom models). For the arXiv e-print example, we will assume just 3 Aggregated Resources (http://arxiv.org/ps/astro-ph/0601007 ; http://arxiv.org/pdf/astro-ph/0601007 ; http://arxiv.org/e-print/astro-ph/0601007). To include these resources in the Aggregation, we must create /feed/entry elements and corresponding /feed/entry/id and /feed/entry/link[@rel="alternate"]/@href elements.

Whether /feed/entry/id (URI-P) should be resolvable or non-resolvable remains an open issue.

The Atom /feed/entry/id elements can be protocol-based URIs, or they can be non-protocol-based URIs (i.e., the URI scheme is not dereferencable). In the examples, we use non-protocol-based URIs for /feed/entry/id elements. Good candidates for non-protocol-based URIs include uuids [RFC4122], tag URIs [RFC4151], and info URIs [RFC4452]. The tag and info schemes are good for conveying semantics in the identifier and uuids are good for opaque identifiers. Three considerations regarding the minting of these identifiers are important:
- The identifiers are relative to the author of the ReM and MUST globally unqiue. For example, if a repository other than arXiv.org aggregated the same three Aggregated Resources, the /feed/entry/id elements would be different in the two ReMs.
- The identifiers need to persist. For example, once an Atom entry is created, that entry should always be served with the same /feed/entry/id.
- Systems that make the Atom feed accessible should consider how this persistence can be achieved. Obviously, storing the Atom identifiers is one approach. But sometimes doing so may cause unwanted overhead. As shown below, values for /feed/entry/id can be generated based on metadata that is available to the system that makes the ReM available.
In our example, arXiv.org has minted Atom identifiers in the tag URI namespace using metadata that pertains to each of the Aggregated Resources within the context of this Aggregation. It should be noted that for each Aggregated Resource, there is a unique combination of values that could be used for the creation of an Atom entry identifier, namely the URI of the ReM itself and the URI of the Aggregated Resource conveyed by the Atom entry. This combination could be used as the seed to achieve a unique re-computable identifier, for example by concatenating the URIs and creating a hash over them.
The Aggregation aggregates the Aggregated Resources by placing the URIs of the Aggregated Resources in the /feed/entry/link[@rel="alternate"]/@href elements. Unlike the values for /feed/entry/id described above which would change based on the author of the ReM (i.e., 1st or 3rd party ReMs), the URIs in the /feed/entry/link[@rel="alternate"]/@href do not change. They are the URIs of the Aggregated Resources, regardless of who is doing the aggregation.

In summary, the URIs in /feed/entry/link[@rel="alternate"]/@href elements identify the resource that is being aggregated and do not change based on who is doing the aggregating. The URIs in /feed/entry/id elements do change based on who is doing the aggregating.

Expanding our skeleton ReM, we now have:

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
 </entry>

</feed>

2.3 Adding Metadata for the Aggregation and Aggregated Resources

There are three approaches for adding metadata to an Aggregation and Aggregated Resources. First, the aggregation can have additional identifiers such as DOIs or Handles, that can be included with multiple /feed/link[@rel="related"]/@href elements. The second is to use Atom elements like /feed/author, /feed/title, /feed/entry/author, and /feed/entry/title to make the ReM more human readable and more usable in standard syndication tools (e.g., Google Reader). The third approach is to aggregate any metadata with its own URI (such as an OAI-PMH record) as a separate Aggregated Resource.

The arXiv example has an info URI ("info:arxiv/astro-ph/0601007v2") and a DOI ("info:doi/10.1142/S0217732306019475") associated with the aggregation and we encode them with /feed/link[@rel="related"]/@href elements. Note, that as in this example, the URIs provided in /feed/link[@rel="related"]/@href might not be resolvable.
In this example, we use the title and authors of the aggregation as the values for /feed/title and /feed/author, respectively. We choose not to provide values for /feed/entry/author, preferring instead to inherit those values from /feed/author (see section 4.2.1 of [ReMProfileofAtom]). Rather than repeat the value of /feed/title in /feed/entry/title, we generate a human-readable value that helps distinguish one Aggregated Resource from another. If the Aggregation had distinctly separate titles for its Aggregated Resources, we use those values for /feed/entry/title accordingly.
Finally, we add a fourth Aggregated Resource, which is the OAI-PMH metadata available from the arXiv e-print repository. Although not required, in this example, we modify the /feed/entry/title to add a human-readable hint that this Aggregated Resource is metadata. To unambiguously mark it as bibliographic metadata, we use appropriate values in /feed/entry/category to mark it as metadata (although in the example below, it uses an Info URI namespace (eu-repo) that is pending registration). Note that under the rules of the Atom Syndication Format, if not otherwise present, /feed/entry/author inherits the value of /feed/author. In this example that is acceptable, but in other scenarios one might want to explicitly set a value (possibly a null value if necessary) for /feed/entry/author.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

2.4 /feed/updated and /feed/entry/updated

Whereas RFC-4287 allows updated to be changed "when an entry or feed was modified in a way the publisher considers significant", the Resource Map Profile of Atom is more strict. The /feed/updated value SHOULD match the "Last-Modified" HTTP response header [RFC2616], if that header exists. If the "Last-Modified" header does not exist (which can happen when a resource is dynamically generated), the /feed/updated MAY be the value in the "Date" HTTP response header (the date the HTTP response was generated). However, in this case of the "Last-Modified" HTTP response header not being available, it is RECOMMENDED that the ReM publisher keep track of what the correct value of /feed/updated should be and strictly update its value based on any modification, significant or not. See section 4.2.15 of [ReMProfileofAtom] for a detailed explanation.

Populating /feed/entry/updated is more subtle. Even in the case of 1st party ReMs (such as the arXiv example explored here), /feed/entry/updated is not the "Last-Modified" HTTP response header of the Aggregated Resource, but rather the last time the Aggregation described by the ReM made an assertion about the Aggregated Resource. In other words, /feed/entry/updated is the datestamp of that particular Atom entry, not the Aggregated Resource described by that entry.

Finally, the value of /feed/updated MUST always be equal to or later in time than the values of all /feed/entry/updated elements.

In our example ReM, we have all the /feed/entry/updated values being the same (in the case of arXiv, like many repositories, all the resources were aggregated at the same time), but we show a different datestamp for /feed/updated to correspond with an edit of the ReM that occurred after aggregating the Aggregated Resources.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

2.5 GRDDL crosswalk from Atom XML to RDF/XML

The up-to-date version of the GRDDL-compliant XSLT to transform an Atom-based serialization of a Resource Map into a serialization in RDF/XML is available at http://www.openarchives.org/ore/0.3/atom-grddl.xsl. In order to allow Atom-based Resource Maps to be readily transformed in this manner, it is RECOMMENDED to add GRDDL namespace and transformation information as attributes to the /feed element.

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

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

3. Common Scenarios

In this section we review the appropriate techniques within the Resource Map Profile of Atom for handling common scenarios for Aggregations.

3.1 Multiple Formats

In the example we have been working with, the PostScript, PDF and the page containing links to other formats are all considered separate Aggregated Resources and not simply the same Aggregated Resource realized in multiple MIME types. This differs from the typical Atom Syndication Format idiom, where multiple MIME types are often grouped in the same /feed/entry element.

We can also express that Aggregated Resources share a format relationship. In this example, we link the PostScript and PDF formats together by placing hasFormat elements (from the dcterms namespace) in each Atom entry, referencing each other. Although it is RECOMMENDED to place these RDF assertions in the corresponding entry elements for readability, they MAY appear anywhere in the ReM. It is also RECOMMENDED that RDF blocks not be nested to ensure greater readability. We use RDF to make the subject and object of the relationship explicit (see section 4.2.16 of [ReMProfileofAtom]).

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/ps/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/pdf/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/pdf/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/ps/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

3.2 Mirror Copies

arXiv maintains many mirrors throughout the world. For example, the the same e-print can be accessed at the mirror repository in Japan with this URI:

http://jp.arxiv.org/abs/astro-ph/0601007

We treat this the same as adding an additional identifier (such as the arXiv info URI) and use the /feed/link[@rel="related"]/@href element.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <link href="http://jp.arxiv.org/abs/astro-ph/0601007" rel="related"/>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/ps/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/pdf/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/pdf/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/ps/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

3.3 Versions

The arXiv example we have been working with is actually version 2 of the e-print. Up until now, we have not distinguished the second (current) version vs. the first (older version). To do so, we import the hasVersion element from the dcterms namespace and place this new metadata element at the Aggregation level. The value of this element is the URI-R of the previous version of the ReM. If we wanted to inform the agent that the older version should be considered deprecated, we would use the replaces element from the same namespace.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <link href="http://jp.arxiv.org/abs/astro-ph/0601007" rel="related"/>
  <rdf:Description rdf:about="http://arxiv.org/rem/astro-ph/0601007">
     <dcterms:hasVersion rdf:resource="http://arxiv.org/rem/astro-ph/0601007v1"/>
  </rdf:Description>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/ps/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/pdf/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/pdf/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/ps/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

3.4 Splash Pages

So-called "splash" pages conventionally serve as a human-readable surrogate for an Aggregation; they are the page where human agents "start". From the point of view of the ReM, they are just another Aggregated Resource, albeit with a /feed/entry/category element indicating to automated agents that one of the Aggregated Resources is distinguished and can serve as the entry point for humans navigating the Aggregation. This is done in the same manner as marking an Aggregated Resource as bibliographic metadata above, using the values from the proposed info:eu-repo/ namespace.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <link href="http://jp.arxiv.org/abs/astro-ph/0601007" rel="related"/>
  <rdf:Description rdf:about="http://arxiv.org/rem/astro-ph/0601007">
     <dcterms:hasVersion rdf:resource="http://arxiv.org/rem/astro-ph/0601007v1"/>
  </rdf:Description>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:abs</id>
   <link href="http://arxiv.org/abs/astro-ph/0601007" rel="alternate" type="text/html"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Splash Page for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/humanStartPage" label="humanStartPage" />
 </entry>

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/ps/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/pdf/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/pdf/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/ps/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

4. Linking to Other Aggregations

The Data Model Document [ORE Model] defines the notion of Aggregations linking to other Aggregations, in whole or in part, with three relationships: ore:aggregates, ore:isAggregatedBy, and ore:lineage. The methods for specifying these relationships in Atom are, respectively, /feed/entry/category, /feed/entry/link[@rel="related"]/@href, and /feed/entry/link[@rel="via"]/@href.

4.1 Multiplely Aggregated Resources

The actual arXiv e-print that we use in our example points to a citation service at citebase.org that takes as an argument an arXiv identifier and determines the other e-prints that cite that e-print, the number of downloads for that e-print, and other services. For this section, we will assume that citebase.org also publishes ReMs that describe Aggregations from the point of view of their repository. Within one of their ReMs, the splash page for our example arXiv e-print is considered an aggregated resource. Since there is a high level of coordination between the two repositories, the arXiv e-print ReM acknowledges that one its Aggregated Resources "isAggregatedBy" another Aggregation. This is done with /feed/entry/link[@rel="related"]/@href within the appropriate /feed/entry. See Table 1 of [ReMProfileofAtom] and section 5.1 of the [ORE Model] for more information.

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://arxiv.org/rem/astro-ph/0601007#aggregation</id>
  <link href="http://arxiv.org/rem/astro-ph/0601007" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator> 
  <updated>2007-10-10T18:30:02Z</updated> 
  <category scheme="http://www.openarchives.org/ore/terms/" 
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
  <link href="info:doi/10.1142/S0217732306019475" rel="related"/>
  <link href="info:arxiv/astro-ph/0601007v2" rel="related"/>
  <link href="http://jp.arxiv.org/abs/astro-ph/0601007" rel="related"/>
  <rdf:Description rdf:about="http://arxiv.org/rem/astro-ph/0601007">
     <dcterms:hasVersion rdf:resource="http://arxiv.org/rem/astro-ph/0601007v1"/>
  </rdf:Description>
  <title>Parametrization of K-essence and Its Kinetic Term</title> 
  <author><name>Hui Li</name></author> 
  <author><name>Zong-Kuan Guo</name></author> 
  <author><name>Yuan-Zhong Zhang</name></author> 

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:abs</id>
   <link href="http://arxiv.org/abs/astro-ph/0601007" rel="alternate" type="text/html"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Splash Page for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/humanStartPage" label="humanStartPage" />
   <link href="http://www.citebase.org/rem?id=oai:arXiv.org:astro-ph/0601007#aggregation" 
   rel="related" />
 </entry>

 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:oai-pmh</id>
   <link href="http://export.arxiv.org/oai2?verb=GetRecord&amp;metadataPrefix=oai_dc&amp;identifier=astro-ph/0601007" 
   rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Dublin Core Metadata for "Parametrization of K-essence and Its Kinetic Term"</title>
   <category scheme="info:eu-repo/semantics/" 
   term="info:eu-repo/semantics/DescriptiveMetadata" label="DescriptiveMetadata" />
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:ps</id>
   <link href="http://arxiv.org/ps/astro-ph/0601007" rel="alternate" type="application/postscript"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PostScript Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/ps/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/pdf/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:pdf</id>
   <link href="http://arxiv.org/pdf/astro-ph/0601007" rel="alternate" type="application/pdf"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>PDF Version of "Parametrization of K-essence and Its Kinetic Term"</title> 
   <rdf:Description rdf:about="http://arxiv.org/pdf/astro-ph/0601007">
	<dcterms:hasFormat rdf:resource="http://arxiv.org/ps/astro-ph/0601007"/>
   </rdf:Description>
 </entry>
 
 <entry>
   <id>tag:arxiv.org,2007:astro-ph/0601007v2:e-print</id>
   <link href="http://arxiv.org/e-print/astro-ph/0601007" rel="alternate"/>
   <updated>2007-05-31T12:52:00Z</updated>
   <title>Other Versions of "Parametrization of K-essence and Its Kinetic Term"</title> 
 </entry>

</feed>

4.2 Lineage

The ore:lineage relation (see seciton 6.3 of [ORE Model] for more information) exists so an Aggregation can provide an unambiguous declaration of origin of the present Aggregated Resource. For example, imagine that a repository took the PDF Aggregated Resource from the arXiv e-print example and modified the PDF so its references are clickable OpenURL links. The new PDF has its own URI, and the /feed/entry/id corresponding to the new PDF is relative to the new repository and does not match the /feed/entry/id from the arXiv example. We can encode this lineage by using a /feed/entry/link[@rel="via"]/@href element with the href value of the arXiv /feed/entry/id. Although in this example, the arXiv /feed/entry/id value is not a resolvable URI, it does uniquely identify the Aggregated Resource within the context of the Aggregation. The value in /feed/entry/link[@rel="via"]/@href is the proxy for the Aggregated Resource as it appears in the original Aggregation (URI-P; see section 6 of [ORE Model] for more information).

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://converter.repo.org/converted/2008-03-30/#aggregation</id>
  <link href="http://converter.repo.org/converted/2008-03-30/" rel="self" type="application/atom+xml"/>
  <generator uri="http://repo.org/">OpenURL PDF Converter Repository</generator>
  <updated>2008-03-30T13:03:20Z</updated>
  <category scheme="http://www.openarchives.org/ore/terms/"
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />

 <!-- other entries -->

 <entry>
   <id>tag:repo.org,2008:astro-ph-0601007.pdf</id>
   <link href="http://repo.org/astro-ph-0601007.pdf" rel="alternate"/>
   <updated>2008-03-30T13:03:20Z</updated>
   <title>"Parametrization of K-essence and Its Kinetic Term" (with OpenURL-enabled references)</title>
   <link href="tag:arxiv.org,2007:astro-ph/0601007v2:pdf" rel="via"/>
 </entry>

 <!-- other entries -->

</feed>

4.3 Nested Aggregations

It is possible to build nested aggregations, where the Aggregated Resource in one Aggregation is another Aggregation. For example, if arXiv.org created an Aggregation for all of its e-prints, then the Aggregated Resources in that Aggregation would be Aggregations corresponding to the e-prints. To provide a hint that the Aggregated Resource is itself an Aggregation, the /feed/entry/category element MAY be used (see section 4.2.2 of [ReMProfileofAtom] for more information).

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
      xmlns:grddl="http://www.w3.org/2003/g/data-view#" 
      grddl:transformation="http://www.openarchives.org/ore/atom-grddl.xsl"
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dcterms="http://purl.org/dc/terms/">

  <id>http://arxiv.org/list/astro-ph/rem/recent/#aggregation</id>
  <link href="http://arxiv.org/list/astro-ph/rem/recent/" rel="self" type="application/atom+xml"/>
  <generator uri="http://arXiv.org/">arXiv.org e-Print Repository</generator>
  <updated>2008-03-31:30:22Z</updated>
  <category scheme="http://www.openarchives.org/ore/terms/"
  term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />

 <!-- other e-print entries -->

 <entry>
   <id>tag:arxiv.org,2008:list/astro-ph-0601007/rem#aggregation</id>
   <link href="http://arxiv.org/rem/astro-ph/0601007#aggregation" 
   type="application/atom+xml" rel="alternate"/>
   <category scheme="http://www.openarchives.org/ore/terms/"
   term="http://www.openarchives.org/ore/terms/Aggregation" label="Aggregation" />
   <updated>2007-10-10T18:30:02Z</updated>
   <title>Parametrization of K-essence and Its Kinetic Term</title>
   <author><name>Hui Li</name></author>
   <author><name>Zong-Kuan Guo</name></author>
   <author><name>Yuan-Zhong Zhang</name></author>
 </entry>

 <!-- other e-print entries -->

</feed>

5. References

[ORE HTTP]: ORE User Guide - HTTP Implementation and Multiple Serializations, C. Lagoze, H. Van de Sompel, P. Johnston, M. Nelson, R. Sanderson, S. Warner, 2008, Available at http://www.openarchives.org/ore/0.3/http.
[ORE Model]: ORE Specification - Abstract Data Model, C. Lagoze, H. Van de Sompel, P. Johnston, M. Nelson, R. Sanderson, S. Warner, 2007, Available at http://www.openarchives.org/ore/0.3/datamodel.
[ReMProfileofAtom]: ORE Specification - Resource Map Profile of Atom, C. Lagoze, H. Van de Sompel, P. Johnston, M. Nelson, R. Sanderson, S. Warner, 2007, Available at http://www.openarchives.org/ore/0.3/atom.
[RFC2119]: IETF RFC 2119: Key words for use in RFCs to Indicate Requirement Levels, S. Bradner, March 1997. Available at http://www.ietf.org/rfc/rfc2119.txt.
[RFC2616]: IETF RFC 2616: Hypertext Transfer Protocol - HTTP/1.1, R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, T. Berners-Lee, June 1999. Available at http://www.ietf.org/rfc/rfc2616.txt.
[RFC4122]: IETF RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace, P. Leach, M. Mealling, R. Salz, July 2005. Available at http://www.ietf.org/rfc/rfc4122.txt.
[RFC4151]: IETF RFC 4151: The 'tag' URI Scheme, T. Kindberg, S. Hawke, October 2005. Available at http://www.ietf.org/rfc/rfc4151.txt.
[RFC4287]: IETF RFC 4287: The Atom Syndication Format, M. Nottingham, R. Sayre, December 2005. Available at http://www.ietf.org/rfc/rfc4287.txt.
[RFC4452]: IETF RFC 4452: The "info" URI Scheme for Information Assets with Identifiers in Public Namespaces, H. Van de Sompel, T. Hammond, Manifest Solutions, S. Weibel, April 2006. Available at http://www.ietf.org/rfc/rfc4452.txt.

Date	Editor	Description
2008-03-31	mln	public alpha 0.3 release
2008-02-29	mln	public alpha 0.2 release
2007-12-10	mln	public alpha 0.1 release
2007-10-15	mln	alpha release to ORE-TC