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Example Application of a Semantics Register

The Search option on the Advanced Search Facility (ASF) Web site demonstrates an application of a Metadata Semantics Register built on the Basic Semantics Register, using either the XML Schema language or the RDF Schema language. 

The ASF Web site search facility is at <http://asf.gils.net/asfsearch.html>. If you enter a search (e.g, find the word "GILS" with "no  field selected"), your hits will be listed with hyperlinks for each hit. If you click the number "1" on the first hit, you will see a locator record. This locator record is in XML format (use "view source" to see the XML structure.)

Looking at this XML locator record, you will see that the top-level element contains the attribute xmlns="/xml-en.rdfs". This XML namespace attribute refers to an application schema. In this case, the "rdfs" file extension shows that the schema is represented using the RDF Schema language. (The equivalent XML Schema language schema would have the file extension of "xsd".) 

The XML Schema defines the XML elements as they are used in this particular instance of  XML. In this case, we are looking at a locator record having elements with English tags (hence the name "xml-en").

Let's say we are interested in the element having the XML English tag "Subject-Terms-Uncontrolled". We can navigate to the schema referenced in the xmlns parameter, /xml-en.rdfs. There, we will find this entry with an rdfDescription ID value equal to "Subject-Terms-Uncontrolled":

<rdf:Description rdf:ID="Subject-Terms-Uncontrolled">
   <rdf:type rdf:resource="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#Property" />
   <rdfs:subPropertyOf rdf:resource="/bsr-gils.rdfs#1133.541.1207.96" />
</rdf:Description>

This entry in the schema asserts that the "Subject-Terms-Uncontrolled" element is a subProperty of an element defined elsewhere. Specifically, the element is defined at a numbered element within the "gils" subset of the Basic Semantics Register ("bsr"). This information is given by the resource reference, /bsr-gils.rdfs#1133.541.1207.96

We have here a machine-processable connection between a particular instance of metadata (the element tagged as "Subject-Terms-Uncontrolled") and its underlying schema (an entry in the Basic Semantics Register). First, the application that generated the XML element with an English tag uses the xmlns parameter. This connects each of its named XML elements to a semantic registers where the meanings, relations, and attributes of elements are defined. In our example application, this register just makes a simple relationship between a tag in some syntax like XML and a language like English. The substance of the actual element definition is carried in a common repository of semantics, here the GILS subset of the Basic Semantics Register. One can follow the subProperty hyperlink for more information about the element that has the English XML tag of "Subject-Terms-Uncontrolled". Navigating to the BSR entry at the target of </bsr-gils.rdfs#1133.541.1207.96> , we find this definition for the Property numbered "1133.541.1207.96":

<rdf:Description rdf:ID="1133.541.1207.96">
   <rdf:type rdf:resource="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#Property" />
   <rdfs:isDefinedBy rdf:resource="/bsr-gils.rdfs#1133.541.1207.96" />
   <rdfs:label xml:lang="en">InformationResource.Subject.UncontrolledTerm.Group</rdfs:label>
   <rdfs:domain rdf:resource="#1133.541.1207" />
   <rdfs:range rdf:resource="#96" />
   <rdfs:comment>The group of terms, not from a controlled vocabulary, associated with the subject of the information resource.</rdfs:comment>
</rdf:Description>

In this example, we have followed a semantics register represented in RDF Schema language. To follow exactly the same example using XML Schema Language, merely change the xmlns attribute filename extension from "rdfs" to "xsd".


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