Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH)

Phil Barker, March 2006. © Heriot-Watt University.You may reproduce all or any part of this presentation but please retain acknowledgement of authorship & copyright. Also I would appreciate it if you let me know how you are using it and sent me any feedback <philb@icbl.hw.ac.uk>

OAI Background• Has origins in ePrints (arXive, CogPrints), dating

back to 1999 – actively seeking wider applicability– Nothing to do with OAIS

• Aims to “facilitate the efficient dissemination of content” – free access to the archives (at least: metadata)– consistent interfaces for archives and service provider– low barrier protocol / effortless implementation (e.g.,

because based on HTTP, XML, DC)

• Now on version 2.0 (June 2002)

OAI-PMH: what’s it all about

• Service providers harvest metadata from data providers.

Requests (HTTP)

Metadata (XML)

Data provider

Metadata(+ resources)

Harv

est

er

Service Provider

Metadata“service”

Adapted from http://www.oaforum.org/tutorial/english/page3.htm

OAI PMH

What can be requested (verb)

• Description of the archive (Identify)• A list of metadata formats supported by

the data provider (ListMetadataFormats)• A list of sets provided (ListSets)• A list of resource identifiers (ListIdentifiers)• Many records (ListRecords)• An individual record (GetRecord)

Example Requests

• http://archive.example.org/oaipmh?verb=Identify

• http:// archive.example.org/oaipmh?verb=ListRecords&metadataPrefix=oai_dc

Metadata Formats

• Metadata may be returned in any XML format• Dublin Core is mandatory

– OAI-PMH specifies the XML schema to use– No single DC element is mandatory

• Other element sets / bindings are optional– Qualified DC (e.g. RDN, NSDL)– MODS (LoC)– LOM (RDN-LTSN)– ODRL (JORUM (I think))– ...

Sets

• A grouping of items made to allow selective harvesting– E.g. all theses– E.g. the Engineering section– E.g. all resources from a given source

• Optional

List Records

• Harvester can ask for specific metadata format for– All available items – All items in a set– All records modified in given date range– (A single item — GetRecord)

• Data provider can return– All relevant records– Some relevant records + resumption token– An error code (no such set / metadata format)

Static Repositories

• Even lighter-weight specification for data providers with small and relatively static collections– E.g. the output from a conference

• Essentially an XML file available at a URL

• Accessed through a “static repository gateway” intermediary

Issues: complexity

• Providing data is easy• Harvesting data is easyHowever• Doing so may lead to complex workflow /

policy issues– What do you do with the harvested metadata?– Do you modify the metadata you harvest?– If so, do you feed this back to the provider?– What if the provider changes a modified record?– Does a service provider disseminate via OAI?

Issues: uptake

• Lots of implementers, who have produced lots of useful support

However• Relatively little commercial uptake• Relatively little support for harvesting

rich metadata• Relatively little support/consensus on

sets

Issues: Harvesting resource (e.g. Full text)

• Nothing in OAI-PMH requires that full-text should be available for harvesting.– Resource may be physical or accessed controlled

• Nothing in OAI-PMH requires that information required for harvesting should be available.

• However in many cases OAI-PMH will provide the information required to harvest the resource.

Further resources

• Open Archives Initiative– http://www.openarchives.org/– Spec, best practice guide and useful resources,

mailing lists

• OAI for beginners– http://www.oaforum.org/tutorial/– Online tutorial

• OAI Repository Explorer– http://www.purl.org/NET/oai_explorer– Web interface for issuing OAI-PMH requests