OAI-PMH Concepts

Requests are made to a repository using the HTTP GET or POST methods. There is a single base URL for all requests. All requests consist of a list of keyword arguments which take the form of key=value pairs. One of the key=value pairs must be the verb key paired with one of the six allowed verb values.

Verb	Description
GetRecord	Retrieve an individual metadata record from the repository. For example: GetRecord
Identify	Retrieve information about a repository. For example: Identify
ListIdentifiers	Retrieve a list of identifiers that uniquely identifies each metadata record in the repository. For example: ListIdentifiers
ListMetadataFormats	Retrieve a list of the metadata formats that the repository supports. For example: ListMetadataFormats
ListRecords	Retrieve all metadata records in the repository. For example: ListRecords
ListSets	Retrieve the sets supported by the repository. Sets are predetermined groups of metadata records that identify related items. For example: ListSets

Additional mandatory and optional arguments are specified depending on the particular verb used.

Responses are returned in the XML format. The structure of the XML is mostly specified by the OAI-PMH. However, requests using the verbs GetRecord or ListRecords contain a metadata record section, the structure of which is specified by the metadataPrefix argument. Take, for example, the request:

http://arXiv.org/oai2?verb=GetRecord&identifier=oai:arXiv.org:cs/0112017&metadataPrefix=oai_dc

The GetRecord verb means that we are attempting to retrieve the metadata record for a specific item in the repository. The identifier argument specifies the particular item we are attempting to retrieve, and the metadataPrefix argument specifies the format of the metadata record section. In the response below, the metadata record section is contained within the <metadata> tags. All other parts of the response are specified by the OAI-PMH:

<?xml version="1.0"?>
<OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/
           http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd">
  <responseDate>2012-12-20T07:37:42Z</responseDate>
  <request verb="GetRecord" identifier="oai:arXiv.org:cs/0112017"
           metadataPrefix="oai_dc">http://export.arxiv.org/oai2</request>
  <GetRecord>
    <record>
      <header>
        <identifier>oai:arXiv.org:cs/0112017</identifier>
        <datestamp>2007-05-23</datestamp>
        <setSpec>cs</setSpec>
      </header>
      <metadata>
        <oai_dc:dc xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/"
                   xmlns:dc="http://purl.org/dc/elements/1.1/"
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                   xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/
                     http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
          <dc:title>Using Structural Metadata to Localize Experience of Digital Content</dc:title>
          <dc:creator>Dushay, Naomi</dc:creator>
          <dc:subject>Computer Science - Digital Libraries</dc:subject>
          <dc:subject>H.3.7</dc:subject>
          <dc:description>
            With the increasing technical sophistication of both 
            information consumers and providers, there is increasing demand
            for more meaningful experiences of digital information. We
            present a framework that separates digital object experience,
            or rendering, from digital object storage and manipulation, so
            the rendering can be tailored to particular communities of
            users. Our framework also accommodates extensible digital
            object behaviors and interoperability. The two key components
            of our approach are 1) exposing structural metadata associated
            with digital objects -- metadata about the labeled access
            points within a digital object and 2) information
            intermediaries called context brokers that match structural
            characteristics of digital objects with mechanisms that produce
            behaviors. These context brokers allow for localized rendering
            of digital information stored externally.
          </dc:description>
          <dc:description>Comment: 23 pages including 2 appendices, 8 figures</dc:description>
          <dc:date>2001-12-14</dc:date>
          <dc:type>text</dc:type>
          <dc:identifier>http://arxiv.org/abs/cs/0112017</dc:identifier>
        </oai_dc:dc>
      </metadata>
    </record>
  </GetRecord>
</OAI-PMH>

Repositories are only required to support one metadata format, unqualified Dublin Core (oai_dc), but may optionally support any number of additional formats. The formats that a repository supports can be queried using the ListMetadataFormats verb.

Sets are an optional OAI-PMH concept that allow repositories to group items. Sets are defined by three elements:

• setSpec: the unique identifier of a set.
• setName: a short string naming the set.
• setDescription: an optional description of the set.

Sets that are exposed by the repository may be listed using the ListSets request. They can also be used to limit the responses to the ListIdentifiers and ListRecords requests using the set argument.

Sets may be organized in a hierarchy. Hierarchical organization is specified by the syntax of the setSpec element. Each hierarchical item in the set is separated in the setSpec by a colon. Take, for example, the sets:

setName	setSpec
Institutions	institution
Oceanside University of Nebraska	institution:nebraska
Valley View University of Florida	institution:florida
Subjects	subject
Existential Kinesiology	subject:kinesiology
Quantum Psychology	subject:quantum

Here we have two main sets, institution and subject, each with two subsets.

The advantages of hierarchical sets are:

• Large sets can be partitioned into logically smaller groups.
• All subsets are returned in response to ListIdentifiers and ListRecords requests using the set argument containing a parent setSpec.

Note: The setSpec element must only contain alphanumeric characters, colons or the characters: - _ . ! ~ * ' ( )