3.5 Interoperability and Crosswalk: Standards and Tools
Interoperability means the provision of exchanging data without minimal loss of content functionality of multiple systems (with different hardware & software platform and data structure interface). A crosswalk is mapping of the elements, semantics and syntax from one metadata schema to those of another so that metadata created by one community can be used by another group that employs a different metadata standard. By Crosswalk, it is possible to use metadata created by one community by another group that may employ different metadata standards. It is useful for virtual collections where resources are drawn from varieties of sources and expected to act as a whole. Interoperability and crosswalk ensures exchange of bibliographic data among heterogeneous systems across the globe. Automated and digital library systems are now supporting various standards and protocols like Z39.50, OAI/PMH, METS (Metadata Encoding and Transmission Standard), MARC-XML, SRU (Search/Retrieval via URL protocol) and SRW (Search /Retrieve Web service protocol) to achieve interoperability. In other words, interoperability is the ability of systems, services and organizations to work together seamlessly toward common or diverse goals. In the technical arena it is supported by open standards for communication between systems and for description of resources and collections, among others. Interoperability is considered here primarily in the context of resource discovery and access. The domain of LIS services uses extensively two interoperability standards – Z 39.50 and OAI/PMH. These two interoperability standards are different in nature. OAI/PMH deals with metadata harvesting whereas Z 39.50 is a protocol for distributed search services. There are some similarities of distributed search services and centralized search services in case of distributed object type, bibliographic world view and object presentation through data provider. Similarly these two interoperability protocols are different in some aspect of searching and semantic mapping. Z39.50 search is basically distributed search whereas OAI based searching is basically centralized searching. In case of Z39.50 protocol search is done by data provider and in OAI protocol search is done by service provider. Semantic mapping is done at the time of searching in Z39.50 protocol and in OAI it is done after metadata delivery. Now, let’s explore the concept of harvesting in order to fetch metadata from OAI-compliant repositories. With the better use of harvesting mechanism we can create centralized search service to consolidate OA contents deposited in OARs. OAI-PMH is based on HTTP, XML and supports unqualified Dublin Core. So implementing such kind of low barrier protocol is quite effortless at the service provider end. OAI is supporting distributed network information services. In that case any organization can create their own harvesting system to fetch data from distributed service providers across the world and may facilitate search service centrally by processing in local server. Let’s see how OAI-PMH mechanism works upon.