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CQL

CQL (the Common Query Language, http://www.loc.gov/cql/) is an abstract and extensible query language designed to provide maximum interoperability between systems, with the minimum difficulty to learn and use, while retaining the functionality to permit complex searches.

CQL was designed for use with SRW, a search protocol successor to Z39.50. Its primary market currently is the bibliographic domain, however it is not limited to this context alone. As such, it provides a standards based and tested mechanism to specify a query that may be used either internally or remotely to select records from a database. The Library of Congress bibliographic database has an SRW/CQL interface available today for all 28 million records.

By using CQL in OpenOffice, a massive amount of data can be located on demand and retrieved for integration within the application. In the first instance this integration can easily be accomplished within the bibliographic subsystem, however in the future it would also, for example, permit standards based collaboration on documents by retrieving OpenOffice documents instead of bibliographic records from appropriate repositories.In order to maintain a consistent user experience, CQL should thus also be used internally for searching the bibliographic database provided as part of the application. The user does not need to use CQL directly, but the system should not be required to treat local and remote queries differently. CQL (the Common Query Language) is an abstract and extensible query language designed to provide maximum interoperability between systems, with the minimum difficulty to learn and use, while retaining the functionality to permit complex searches.

CQL was designed for use with SRW, a search protocol successor to Z39.50. Its primary market currently is the bibliographic domain, however it is not limited to this context alone. As such, it provides a standards based and tested mechanism to specify a query that may be used either internally or remotely to select records from a database. The Library of Congress bibliographic database has an SRW/CQL interface available today for all 28 million records.By using CQL in OpenOffice, a massive amount of data can be located on demand and retrieved for integration within the application. In the first instance this integration can easily be accomplished within the bibliographic subsystem, however in the future it would also, for example, permit standards based collaboration on documents by retrieving OpenOffice documents instead of bibliographic records from appropriate repositories.

In order to maintain a consistent user experience, CQL should thus also be used internally for searching the bibliographic database provided as part of the application. The user does not need to use CQL directly, but the system should not be required to treat local and remote queries differently.

SRW

SRW (http://www.loc.gov/z3950/agency/) is the "Search/Retrieve Web Service" protocol, which aims to integrate access to various networked resources, and to promote interoperability between distributed databases, by providing a common utilization framework. SRW is a web-service-based protocol whose underpinnings are formed by bringing together more than 20 years experience from the collective implementers of the Z39.50 Information Retrieval protocol with recent developments in the web technologies arena.

SRW features both SOAP and URL-based access mechanisms to provide for a wide variety of possible clients ranging from Microsoft's .Net initiative to simple Javascript and XSLT transformations. It leverages the CQL query language which provides a powerful yet intuitive means to formulate searches. The protocol mandates the use of open and industry-supported standards XML and XML Schema, and where appropriate, XPath and SOAP. SRW has been developed by an international team, minimizing cross-language pitfalls and other potential internationalization problems.

The SRW Initiative, building on Z39.50 along with web technologies, recognizes the importance of Z39.50 (as currently defined and deployed) for business communication, and focuses on getting information to the user. SRW provides semantics for searching databases containing metadata and objects, both text and non-text. Building on Z39.50 semantics enables the creation of gateways to existing Z39.50 systems while reducing the barriers to new information providers, to make their resources available via a standard search and retrieve service.

SRW defines a web service combining several Z39.50 features, most notably, the Search, Present, and Sort Services. Additional features/services may be added later or defined later as new web services. Also see srw.cheshire3.org

SRU

The difference between SRU and SRW is that SRU uses HTTP as the transport mechanism. This means that the query itself is transmitted as an URL and that XML is returned as if it were a web page (note: POST, an alternative for using the HTPP transport mechanism, is not allowed in SRU). SRW is SOAP based, meaning that both the query and the result are XML streams. The advantage of this is that a variety of transport mechanisms can be used, including for instance e-mail.

Z39.50

Z39.50 (http://www.loc.gov/z3950/agency/) is a national and international (ISO 23950) standard defining a protocol for computer-to-computer information retrieval. Z39.50 makes it possible for a user in one system to search and retrieve information from other computer systems (that have also implemented Z39.50) without knowing the search syntax that is used by those other systems. Z39.50 was originally approved by the National Information Standards Organization (NISO) in 1988.

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