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<!--
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* metacatquery.html
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*
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* Authors: Jivka Bojilova
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* Copyright: 2000 Regents of the University of California and the
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* National Center for Ecological Analysis and Synthesis
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* For Details: http://www.nceas.ucsb.edu/
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* Created: 2000 April 5
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* Version: 0.01
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* File Info: '$Id$'
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*
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* October Meeting SDSC, 2000
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-->
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<HTML>
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<HEAD>
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<TITLE>Metacat</TITLE>
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<link rel="stylesheet" type="text/css" href="./default.css">
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</HEAD>
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<BODY>
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<table width="100%">
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<tr>
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<td class="tablehead" colspan="2"><p class="label">Queries and Results</p></td>
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<td class="tablehead" colspan="2" align="right">
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<a href="./metacatload.html">Back</a> | <a href="./metacattour.html">Home</a> |
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<a href="./metacatread.html">Next</a>
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</td>
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</tr>
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</table>
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<P>The Metacat Server provides
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an interface for searching of metadata stored in the Metacat database.
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<P> <img alt="architecture diagram of a Metacat query" src="metadataquery.gif">
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<br><br><b>Steps to perform a query in Metacat</b>
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<ol>
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<li>A pathquery document is created from the search criteria provided through
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the servlet parameters.</li>
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<li>This pathquery document is sent to DBQuery where it
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is processed and translated into SQL statements.</li>
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<li>The SQL statements are executed against the database and the resultsets
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are translated into an xml document of doctype "resultset".</li>
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<li>The resultset document is either returned directly to the client as XML
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or is transformed through XSLT and returned as HTML.</li>
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</ol>
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<b>The Pathquery Document</b>
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<pre>
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<pathquery version="1.0">
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<meta_file_id>unspecified</meta_file_id>
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<querytitle>unspecified</querytitle>
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<returnfield>dataset/title</returnfield>
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<returnfield>keyword</returnfield>
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<returnfield>originator/individualName/surName</returnfield>
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<returndoctype>eml://ecoinformatics.org/eml-2.0.1</returndoctype>
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<returndoctype>eml://ecoinformatics.org/eml-2.0.0</returndoctype>
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<querygroup operator="UNION">
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<queryterm casesensitive="false" searchmode="contains">
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<value>Plant</value>
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<pathexpr>dataset/title</pathexpr>
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</queryterm>
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<queryterm casesensitive="false" searchmode="contains">
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<value>plant</value>
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<pathexpr>keyword</pathexpr>
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</queryterm>
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</querygroup>
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</pathquery>
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</pre>
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<p>The pathquery document was designed to be flexible enough to query specific
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fields of any XML document. It also allows the client to specify which fields
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from a returned document are returned in the initial resultset. Each
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<returnfield> parameter specifies a field which the DB will return
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for any query hit. The returndoctype fields allows the client to limit the
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type of documents to be returned. If no returndoctype element , all document types are returned.
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A <querygroup> creates an AND or an OR statement of the <queryterm>s
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in the group. The operator can be UNION or INTERSECT. A <queryterm>
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defines the actual field against which the query is being performed. The value
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of the queryterm that we are quering for is encased in <value> tags.
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The <pathexpr> tag specifies an exact path to which you want to restrict
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the search. A <pathexpr> tag which contains the keyword returndoc is
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a special case which is discussed in <a href="./packages.html">Packages and
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Relations</a>.</p><br>
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<b>The Resultset Document</b><br>
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<p>When the pathquery document is submitted and processed, Metacat returns
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another XML document called a resultset document.<p>
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<pre>
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<resultset>
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<query>
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<pathquery version="1.0">
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<meta_file_id>unspecified</meta_file_id>
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<querytitle>unspecified</querytitle>
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<returnfield>dataset/title</returnfield>
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<returnfield>keyword</returnfield>
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<returnfield>originator/individualName/surName</returnfield>
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<returndoctype>eml://ecoinformatics.org/eml-2.0.1</returndoctype>
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<returndoctype>eml://ecoinformatics.org/eml-2.0.0</returndoctype>
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<querygroup operator="UNION">
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<queryterm casesensitive="false" searchmode="contains">
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<value>Datos</value>
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<pathexpr>dataset/title</pathexpr>
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</queryterm>
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<queryterm casesensitive="false" searchmode="contains">
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<value>plant</value>
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<pathexpr>keyword</pathexpr>
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</queryterm>
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</querygroup>
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</pathquery>
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</query>
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<document>
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<docid>nceas.44.1</docid>
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<docname>resource</docname>
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<doctype>eml://ecoinformatics.org/eml-2.0.1</doctype>
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<createdate>2001-01-12 16:12:06.0</createdate>
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<updatedate>2001-01-12 16:12:06.0</updatedate>
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<param name="dataset/title">Datos Meteorologicos</param>
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<param name="keyword">intertidal</param>
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<param name="originator/individualName/surName">Smith</param>
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</document>
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<document>
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<docid>nceas.42.1</docid>
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<docname>resource</docname>
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<doctype>eml://ecoinformatics.org/eml-2.0.1</doctype>
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<createdate>2001-01-12 16:11:31.0</createdate>
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<updatedate>2001-01-12 16:11:31.0</updatedate>
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<param name="dataset/title">Ocean Surface Temperature</param>
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<param name="keyword">Plant</param>
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<param name="originator/individualName/surName">Henry</param>
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</document>
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.....
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</resultset>
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</pre>
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<p>The first element in the resultset is <query>. Its content is just
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the pathquery document. The resultset always returns
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the pathquery document that created it in the <query> tag. The next
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major tag is <document>. Each XML document returned by the query
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is represented by a <document> tag. The default document information returned
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is docid, docname, doctype, doctitle, createdate and
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updatedate. The param tags are present if the document found contained
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the returnfield chosen in the pathquery document. The name attribute of the
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param tag is the full path to the node specified by the returnfield. <p>
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<br>
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<a href="./metacatload.html">Back</a> | <a href="./metacattour.html">Home</a> |
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<a href="./metacatread.html">Next</a>
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</BODY>
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</HTML>
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