1 Presented to Query Language '98 December 4, 1998 by Eliot Christian U.S. Geological Survey XML Encoding Rules (XER)

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: zappropriate ASN.1 encoded structures into equivalent XML structures zappropriate XML encoded structures into equivalent ASN.1 structures

5 Opportunities XML developers zleverage investments in ASN.1-based applications already interoperable ASN.1 developers zleverage 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) zXER initial focus is the Z39.50 (ISO Information Search and Retrieval) protocol zIn the Z39.50 community of applications, ASN.1 is used only with BER zInitial 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 1 mwcat [ query on next slide ]

9 XML Encoding: Query Detail CIP [operand next slide] [operand next slide] AND

10 XML Encoding: Operand Detail CreationDate Greater Than or Equal Date

11 XML Encoding: SearchResponse

12 Relevance of Z39.50 zZ39.50 is widespread and growing throughout the library and information services community zMany 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 zFacilitates Z39.50 search of Internet resources zCreates document-level and summary-level XML "locator records" (content with network context) zGILS-compliant, supports STAS, GEO, WhoIs++ zFreeware and commercial products available

14 Semantic Map zA simple XML mechanism to communicate a few important aspects of metadata zNot a global solution or comprehensive registry zBorrows from ISO EDI Basic Semantic Registry zFollows ISO guidance zInitial 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 context ( context-id?, tag?, linkage?, data-type?, occurrence?, definition?, concept-class?, representation? )>

16 URL References XER home page Advanced Search Facility Semantic Map proposal