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<h2><a name="CQL" id="CQL">CQL</a></h2>

<p>CQL (the Common Query Language, <a>http://www.loc.gov/cql/</a>) 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.</p>

<p>CQL was designed for use with <a href="#SRW">SRW</a>, a search protocol
successor to <a href="#Z39.50">Z39.50</a>. 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.</p>

<p>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.</p>

<p>CQL was designed for use with <a href="#SRW">SRW</a>, a search protocol
successor to <a href="#Z39.50">Z39.50</a>. 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.</p>

<p>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.</p>

<h2><a name="SRW" id="SRW">SRW</a></h2>

<p>SRW <a
href="http://www.loc.gov/z3950/agency/">(http://www.loc.gov/z3950/agency/)</a>
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 <a href="#Z39.50">Z39.50</a> Information Retrieval protocol with recent
developments in the web technologies arena.</p>

<p>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.</p>

<p>The SRW Initiative, building on <a href="#Z39.50">Z39.50</a> along with
web technologies, recognizes the importance of <a href="#Z39.50">Z39.50</a>
(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 <a href="#Z39.50">Z39.50</a> semantics enables the creation of gateways to
existing <a href="#Z39.50">Z39.50</a> systems while reducing the barriers to
new information providers, to make their resources available via a standard
search and retrieve service.</p>

<p>SRW defines a web service combining several <a href="#Z39.50">Z39.50</a>
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 <a href="http://srw.cheshire3.org">srw.cheshire3.org</a></p>

<h2><a name="SRU" id="SRU">SRU</a></h2>

<p>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.</p>

<h2><a name="Z39.50" id="Z39.50">Z39.50</a></h2>

<p>Z39.50 <a
href="http://www.loc.gov/z3950/agency/">(http://www.loc.gov/z3950/agency/)</a>
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.</p>

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