Newsletter Discussion

Abstract

OAI-PMH is a lightweight harvesting protocol for sharing metadata between services. A Data Provider maintains one or more repositories (web servers) that support the OAI-PMH as a means of exposing data. A Service Provider issues OAI-PMH requests to data providers and uses the metadata as a basis for building value-added services. The OAI-PMH Requests must be submitted using the GET or POST methods of HTTP. The OAI Responses are formatted as HTTP responses.

OAI Protocol for Metadata Harvesting

OAI stands for open archives initiative. This has been initiated by the e-print community. The aim is to enable access to web-accessible material through interoperable repositories for metadata sharing, publishing and archiving. This has been initiated as there is a growing need for a low-barrier interoperability solution to access across fairly heterogeneous repositories.

OAI-PMH is a lightweight harvesting protocol for sharing metadata between services. A Data Provider maintains one or more repositories (web servers) that support the OAI-PMH as a means of exposing metadata. A Service Provider issues OAI-PMH requests to data providers and uses the metadata as a basis for building value-added services. Harvesting refers specifically to the gathering together of metadata from a number of distributed repositories into a combined data store.

The OAI-PMH Requests must be submitted using the GET or POST methods of HTTP. At least one key=value pair (verb=RequestType) must be provided. Additional key=value pairs depend on the request type.

The following are the OAI-PMH request types

• 1. Identify
• 2. ListMetadataFormats
• 3. ListSets
• 4. ListIdentifiers
• 5. ListRecords
• 6. GetRecord

The OAI-PMH Responses are formatted as HTTP responses. The response format must be well-formed XML.

The response has the following structure

• 1. XML declaration

  (<?xml version="1.0"encoding="UTF-8" ?>)

• 2. Root element named OAI-PMH with three attributes

  (xmlns, xmlns:xsi, xsi:schemaLocation)

• 3. Three child elements

  1. ResponseDate (UTC datetime)

  2. Request (the request that generated this response)

  3a) error (in case of an error or exception condition)

  3b) element with the name of the OAI-PMH request

As a well formed xml it can be interoperable over the fairly heterogeneous repositories. But the problem with this protocol is that it is limited to some seven types of request types. As there is more description about the available objects now we need a better protocol which can be extended over the time.