Download OAI-Intro

Open Archives
Initiative
Protocol for Metadata
Harvesting
Collections in isolation
 Some thoughts
 A wonderful collection is of limited
use if it is not well known.
 Very redundant collections are
often wasteful
Virtual collections
 Some collections do not contain actual
materials, only information about materials
and links to the home site.
 How do these virtual collections get the
information about other collections? How do
they stay up to date?
 --> The Open Archives Initiative Protocol for
Metadata Harvesting (OAI-PMH)
OAI - PMH
 A protocol -- that is just an agreement to
exchange messages and interpret them
according to strict rules.
 Metadata -- data about the data -information about the material in the
collection
 Harvesting -- gathering in the desired
part of the collection for further use
The protocol
 See http://www.openarchives.org/OAI/openarchivesprotocol.html
 Two sides - the repository and the harvestor
 The repository (data providers)
 Prepares the required metadata
 Responds to the harvester queries
 Acts like a server - responding to queries when they
come
 The Harvester (data gatherer)
 Gathers the metadata from the collections
 Organizes the harvested metadata in a way to serve its
purpose.
 Acts like a client - requesting service when it needs it.
Resource, item, record
 Resource: the actual content of the collection; the
point of the digital library
 Item: a part of the repository that generates the
metadata.
 Record: metadata in a specific format available for
dissemination.
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Encoded in XML
Unique identifier
Datestamp
setSpecµ
Optional status
Sets
 Repositories may organize items into sets
 Allows selective harvesting
 Each node in a set organization has
 setSpec

Set may be hierarchical. If so, the levels are
separated by colons
 setName
 setDescription
Requests
 Request embedded in an HTTP request
 Valid OAI PMH Requests:
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GetRecord
Identify
ListIdentifiers
ListMetadataFormats
ListRecords
ListSets
GetRecord
 Required arguments
 Identifier = unique identifier of an item whose record is
requested
 metadataPrefix = prefix part of the metadata record
relevant to the requested item

This identifies the type of metadata applied to the record.
Example = oai_dc (the OAI version of the Dublin Core -standard 15 elements, no extension.)
 Errors: badArgument, cannotDisseminateFormat,
idDoesNotExist
Identify
 No arguments
 Requests information about the repository.
 Response includes
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repositoryName
BaseURL
protocolVersion
earliestDatestamp
deletedRecord (how does the repository handle
deletions -- no, transient, persistent
Granularity (how finely can the datestamp be
specified?)
adminEmail
compression (what schemes are supported)
description
Optional
ListIdentifiers
 Required Argument
 metadataPrefix
 Optional Arguments
 from
 until
 set
 Exclusive argument
 resumptionToken (flow control token for resuming an
incompleted previous ListIdentifiers request)
 Errors: badArgument, badResumptionToken,
cannotDisseminateFormat, noRecordsMatch,
noSetHierarchy
ListMetadataFormats
 Optional argument
 identifier (if metadataformat is needed only for
some particular item)
 Errors - badArgument, idDoesNotExist,
noMetadataFormats
 Response includes both metadataPrefix and
the associated schema
ListRecords
 Required arguments
 metadataPrefix - Only records for which the specified
metadataPrefix applies should be returned
 Optional arguments
 from
 until
 set
 Exclusive arguments
 resumtpionToken
ListSets
 Exclusive Argument
 resumptionToken (used to continue a previous
incomplete response to ListSets)
 Errors - badArgument, badResumtpionToken,
noSetHierarchy
Resources
 Compliance testing www.dlib.vt.edu/projects/OAI/repexp/repexp.html
 OAI PMH www.openarchives.org/OAI/openarchivesprotocol.html
 Implementation Guidelines
www.openarchives.org/OAI/2.0/guidelines.htm