ORE User Guide - Data Model Overview

8 January 2008


This document was part of an alpha release and has been superseded.

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Editors (OAI Executive)
Carl Lagoze, Cornell University Information Science
Herbert Van de Sompel, Los Alamos National Laboratory
Editors (ORE Technical Committee)
Pete Johnston, Eduserv Foundation
Michael Nelson, Old Dominion University
Robert Sanderson, University of Liverpool
Simeon Warner, Cornell University Information Science


Open Archives Initiative Object Reuse and Exchange (OAI-ORE) defines standards for the description and exchange of aggregations of Web resources. This document provides a brief overview of the abstract data model that is the foundation for these standards. The data model is described in detail in [Data Model]. This user guide is one of several documents comprising the OAI-ORE specification and user guide.

Table of Contents

1. Introduction
2. Foundations
3. Aggregation
4. Resource Map
5. Relationships to other Aggregations
6. References


A. Acknowledgements
B. Change Log

1. Introduction

The ORE Model makes it possible to associate an identity with aggregations of web resources and to describe their structure and semantics. It does this by introducing the Resource Map (ReM), which is a resource identified by a URI (say ReM-1) that encapsulates a set of RDF statements. These statements instantiate an aggregation as a resource with a URI, enumerate the constituents of the aggregation, the relationships among those constituents, and the Web context of the aggregation. The ORE Model can be serialized in a variety of formats which will be described, along with mappings of ORE Model concepts, in companion ORE documents. At present, only an Atom serialization [ORE Atom User Guide] [ORE Atom Profile] has been defined.

2. Foundations

The ORE Model is based on the Web Architecture in which a unit of information is called a Resource and is identified by a URI. Some URIs are based on common protocols, such as HTTP, and can be dereferenced to yield Representations. The ORE Model also uses RDF triples to make statements that relate a subject resource to an object resource or literal via a predicate (relationship). Example triples might include (in N3 format):

# resource URI-1 has type T-1, and was created by Joe Bloggs
<URI-1>  rdf:type    <T-1>.
<URI-1>  dc:creator  "Joe Bloggs".

meaning that resource URI-1 has type denoted with the URI T-1, and was created by Joe Bloggs. The ORE Model uses predicates from a number of vocabularies and in this document we use the following namespace prefixes.

Prefix Namespace URI Description
dc Dublin Core elements
dcterms Dublin Core terms
ore ORE vocabulary terms
owl OWL vocabulary terms
rdf RDF vocabulary terms

3. Aggregation

A Resource Map describes an Aggregation which is a set of resources, and possibly their types and relationships among the resources. Resources in the Aggregation are called Aggregated Resources.

In order to be able to talk about the Aggregation on the web, it must have a URI (say A-1). This URI is constructed by appending #aggregation to the Resource Map URI, i.e. ReM-1#aggregation. This syntactic device ensures that there is a unique Aggregation resource for every Resource Map.

4. Resource Map

The following figure shows a complete Resource Map with statements indicated as arrows from subject resource to object resource or literal.  The remainder of this section explains the components of this graph step-by-step.

A complete Resource Map

The Resource Map is identified by ReM-1 and an HTTP GET on ReM-1 must yield a serialization of the Resource Map. Note also that ReM-1 appears as a node in the figure and is the subject of several triples. First, there must be triples providing the type of the Resource Map, the type of the Aggregation, and linking the Resource Map to the Aggregation that it describes:

# mandatory, ReM-1 is a Resource Map (shown as T-1)
<ReM-1>  rdf:type            ore:ResourceMap.

# mandatory, A-1 in an Aggregation (shown as T-2)
<A-1>    rdf:type            ore:Aggregation.

# mandatory, ReM-1 describes A-1
<ReM-1>  ore:describes       <A-1>.

Some metadata about the Resource Map is mandatory, and additional metadata may optionally be expressed:

# mandatory: authoring authority and modification time of ReM
<ReM-1>  dc:creator          "Joe Bloggs".
<ReM-1>  dcterms:modified    "2007-10-15T00:00:00Z".

# optional: rights pertaining to and original creation time of ReM
<ReM-1>  dc:rights           <>.
<ReM-1>  dcterms:created     "2007-10-15T00:00:00Z".

If the Aggregation denotes an information object that has other identifiers then these are expressed using the owl:sameAs predicate:

There is some uncertainty over whether this is an appropriate use of owl:sameAs, which by some interpretations implies an exact equivalence between the subject and object of triples with this predicate. We do not mean exact equivalence but an assertion of semantic equivalence.
<A-1>    owl:sameAs          <DOI-1>.

All of the Aggregated Resources are linked to the Aggregation with the ore:aggregates predicate and may optionally be typed as ore:AggregatedResource:

<A-1>    ore:aggregates      <AR-1>.
<A-1>    ore:aggregates      <AR-2>.
<A-1>    ore:aggregates      <AR-3>.

# optional declarations of types
<AR-1>   rdf:type            ore:AggregatedResource.
<AR-2>   rdf:type            ore:AggregatedResource.
<AR-3>   rdf:type            ore:AggregatedResource.

Thus far, the Aggregation is just a bag of resources, AR-1, AR-2, and AR-3, unrelated except for their status as constituents of the Aggregation. A Resource Map may also describe the structure of the Aggregation by expressing internal relationships between the Aggregation and/or Aggregated Resources, for example:

# shown as R-1
<AR-2>   dc:hasFormat        <AR-3>.

Finally, the Resource Map may include two types of external relationships: 1) Semantic types may be associated with either the Aggregation and/or the Aggregeted Resources using the rdf:type predicate. 2) The context of the Aggregation among other other resources may be expressed using predicates in any vocabulary provided either the subject or object is the Aggregation or and Aggregated Resource.

# A-1 has type T-4 (journal article perhaps) and is part of resource A
<A-1>    rdf:type            <T-4>.
<A-1>    dcterms:isPartOf    <A>.

# AR-1 references B (perhaps another article) and has type Text
<AR-1>   dcterms:references  <B>.
<AR-3>   rdf:type            <>.

5. Relationships to other Aggregations

When reusing Resource Maps and the Aggregations that they descibe, it is important to remember the distinction between these two concepts. Statements about ReM-1 are statements about the Resource Map and not the Aggregation; statements about A-1 (= ReM-1#aggregation) are statements about the intellectual object that is the Aggregation.

An Aggregated Resource may be aggregated in more than one Aggregation (say A-1 and A-2). The predicate ore:isAggregatedBy is the inverse of ore:aggregates and allows membership in another Aggregation to be expressed.

# Creator of ReM-1 knows AR-1 aggregated by A-2 as well as A-1
<AR-1>   ore:isAggregatedBy  <A-2>.

The Resource Map describing A-2 is naturally obtained when the fragment identifier part of A-2 is removed (leaving ReM-2 since A-2 = ReM-2#aggregation) in the process of dereferencing A-2.

A second use of ore:isAggregatedBy is to indicate nesting, where one Aggregation an Aggregated Resource in another Aggregation. Image that A-1 is a journal article which is part of a journal issue (Aggregation A-3). This context can be expressed in ReM-1 with the following triple.

# ReM-1 indicates that aggregation A-1 is aggregated by A-3
<A-1>    ore:isAggregatedBy  <A-3>.

6. References

[Data Model]
ORE Specification - Abstract Data Model, Carl Lagoze, Herbert Van de Sompel, Pete Johnston, Michael Nelson, Robert Sanderson, Simeon Warner (editors), 2007-12-10. Available at
[ORE Atom User Guide]
ORE User Guide - Resource Map Implementation in Atom, Carl Lagoze, Herbert Van de Sompel, Pete Johnston, Michael Nelson, Robert Sanderson, Simeon Warner (editors), 2007-12-10. Available at
[ORE Atom Profile]
ORE Specification - Resource Map Profile of Atom, Carl Lagoze, Herbert Van de Sompel, Pete Johnston, Michael Nelson, Robert Sanderson, Simeon Warner (editors), 2007-12-10. Available at

A. Acknowledgements

This document is the work of the Open Archives Initiative. Funding for Open Archives Initiative Object Reuse and Exchange is provided by the Andrew W. Mellon Foundation, Microsoft, and the National Science Foundation.  Additional support is provided by the Coalition for Networked Information.

This document is based on meetings of the OAI-ORE Technical Committee (ORE-TC), with participation from the OAI-ORE Liaison Group (ORE-LG).  Members of the ORE-TC are: Chris Bizer (Freie Universität Berlin), Les Carr (University of Southampton), Tim DiLauro (Johns Hopkins University), Leigh Dodds (Ingenta), David Fulker (UCAR), Tony Hammond (Nature Publishing Group), Pete Johnston (Eduserv Foundation), Richard Jones (Imperial College), Peter Murray (OhioLINK), Michael Nelson (Old Dominion University), Ray Plante (NCSA and National Virtual Observatory), Rob Sanderson (University of Liverpool), Simeon Warner (Cornell University), and Jeff Young (OCLC).  Members of ORE-LG are: Leonardo Candela (DRIVER), Tim Cole (DLF Aquifer and UIUC Library), Julie Allinson (JISC), Jane Hunter (DEST), Savas Parastatidis  (Microsoft), Sandy Payette (Fedora Commons), Thomas Place (DARE and University of Tilburg), Andy Powell (DCMI), and Robert Tansley (Google, Inc. and DSpace)

We also acknowledge comments from the OAI-ORE Advisory Committee (ORE-AC).

B. Change Log

Date Editor Description
2008-01-08 simeon correct N3 example
2007-12-10 simeon public alpha release
2007-10-15 simeon alpha release to ORE-TC

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