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XML Encoding Rules (XER)

XML Encoding Rules (XER). Presented to Query Language '98 December 4, 1998 by Eliot Christian U.S. Geological Survey. Immediate Need (Nov. 1998). An abstract specification of search was needed to respond to the OpenGIS Consortium RFP for Catalog Services (CORBA, COM, Z39.50, SQL, and LDAP)

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XML Encoding Rules (XER)

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  1. XML Encoding Rules (XER) Presented toQuery Language '98 December 4, 1998 byEliot ChristianU.S. Geological Survey

  2. Immediate Need (Nov. 1998) An abstract specification of search was needed to respond to the OpenGIS Consortium RFP for Catalog Services (CORBA, COM, Z39.50, SQL, and LDAP) XML chosen as the notational syntax for the catalog services search specification

  3. XML to XER XER constrains the XML specification of the search service to assure interoperability with existing Clearinghouse for Geospatial Metadata, other GILS and Z39.50 catalog systems

  4. Basic Concept of XER Analog to ASN.1 (Abstract Syntax Notation), BER (Basic Encoding Rules) Standardized rules for transforming: • appropriate ASN.1 encoded structures into equivalent XML structures • appropriate XML encoded structures into equivalent ASN.1 structures

  5. Opportunities XML developers • leverage investments in ASN.1-based applications already interoperable ASN.1 developers • leverage investments in XML-based applications coming up on the Internet

  6. Initial Scope ASN.1 is used in a variety of applications, protocols, and network environments with various encoding rules (BER, PER, DER) • XER initial focus is the Z39.50 (ISO 23950 Information Search and Retrieval) protocol • In the Z39.50 community of applications, ASN.1 is used only with BER • Initial XER specification compatible with HTTP over the Internet

  7. ASN.1/Z39.50 Fragments PDU ::= CHOICE{searchRequest [22] IMPLICIT SearchRequest,searchResponse [23] IMPLICIT SearchResponse, SearchRequest ::= SEQUENCE{resultSetName [17] IMPLICIT InternationalString,databaseNames [18] IMPLICIT SEQUENCE OF DatabaseName,query [21] Query, SearchResponse ::= SEQUENCE{resultCount [23] IMPLICIT INTEGER,numberOfRecordsReturned [24] IMPLICIT INTEGER,nextResultSetPosition [25] IMPLICIT INTEGER,searchStatus [22] IMPLICIT BOOLEAN,resultSetStatus [26] IMPLICIT INTEGER,records Records OPTIONAL,

  8. XML Encoding: SearchRequest <?xml version='1.0' ?><ISO23950> <searchRequest> <resultSetName> 1 </resultSetName> <databaseNames> mwcat </databaseNames> <query> [ query on next slide ] </query> </searchRequest></ISO23950>

  9. XML Encoding: Query Detail <query> <type-1> <rpnQuery> <attributeSet> CIP </attributeSet> <rpn> <rpn> [operand next slide] </rpn> <rpn> [operand next slide] </rpn> <operator> AND </operator> </rpn> </rpnQuery> </type-1></query>

  10. XML Encoding: Operand Detail <operand> <attributeValue> CreationDate </attributeValue> <attributeValue> Greater Than or Equal </attributeValue> <attributeValue> Date </attributeValue> <term> 1995-01-01 </term></operand>

  11. XML Encoding: SearchResponse <?xml version='1.0' ?><ISO23950> <searchResponse> <resultCount> 76 </resultCount> <numberOfRecordsReturned>0 </numberOfRecordsReturned> <nextResultSetPosition> 0 </nextResultSetPosition> <searchStatus> <true/></searchStatus> </searchResponse></ISO23950>

  12. Relevance of Z39.50 • Z39.50 is widespread and growing throughout the library and information services community • Many hundreds of valuable resources reachable through Z39.50 (e.g., Library of Congress, National Library of Medicine, Spatial Data Infrastructure, environmental data, … )

  13. Advanced Search Facility • Facilitates Z39.50 search of Internet resources • Creates document-level and summary-level XML "locator records" (content with network context) • GILS-compliant, supports STAS, GEO, WhoIs++ • Freeware and commercial products available

  14. Semantic Map • A simple XML mechanism to communicate a few important aspects of metadata • Not a global solution or comprehensive registry • Borrows from ISO EDI Basic Semantic Registry • Follows ISO 11179 guidance • Initial example has 100 common metadata elements in several contexts ("registries"), e.g. title, author, subject, date-of-publication, place-of-publication, language, abstract, place, bounding-coordinates, time-period, medium ...

  15. Semantic Map DTD <!ELEMENT semantic-map ( semantic-unit*)> <!ELEMENT semantic-unit ( context*)> <!ELEMENT context ( context-id?, tag?, linkage?, data-type?, occurrence?, definition?, concept-class?, representation? )>

  16. URL References XER home page <http://asf.gils.net/xer> Advanced Search Facility<http://asf.gils.net> Semantic Map proposal<http://asf.gils.net/semantic_map.html>

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