Z39.50 as a Web Service

Ralph LeVanResearch Scientist

Roadmap

• Why Z39.50 as a Web Service?– The Weaknesses of Classic Z39.50

• The Strengths of Classic Z39.50• SRW: Search and Retrieve on the Web• SRU: Search and Retrieve with URL’s• Outlook for SRW/SRU

The Weaknesses of Classic Z39.50

• Not popular with the Web community– Connection-based Sessions– Binary Encoding– Transmitted directly over TCP/IP

• Complicated

Z39.50 Complicated?

• 11 Native Services– Init, Search, Present, DeleteResultSet,

AccessControl, ResourceControl, TriggerResourceControl, ResourceReport, Scan, Sort, Segment.

• 7 Extended Services– PersistentResultSet, PersistentQuery,

PeriodicQuerySchedule, ItemOrder, DatabaseUpdate, ExportSpecification, ExportInvocation

Z39.50 Complicated?

• 156 page standard– 147 in the 2002 draft

• Vocabulary from the OSI community– Target, Origin, APDU, A-association, Z-

association..• Records described with ASN.1• Attribute Sets

The Strengths of Classic Z39.50

• Result Sets (a.k.a. Statefulness)• Abstraction

– Abstract Access Points (Attribute Sets)– Abstract Record Schemas

• Explain

SRW: Search and Retrieve on the Web• SOAP (Simple Object Access Protocol)

Based– HTTP– XML

• Records Described in WSDL (Web Service Description Language)

• 1 Service: SearchAndRetrieve• No Documentation :-)

Semantically equivalent to classic Z39.50• Gateways Trivial• Preserves the experience of the ZIG

without the baggage of the standard• Syntactic equivalence discounted

SRW: The Basics

• Only one database per request• String (not structure) based queries• Index Sets, not Attribute Sets• One Record Syntax (XML)

The SRW Request

• String Query• Integer StartRecord• Integer MaximumRecords• String RecordSchema

The SRW Response

• String ResultSetReference– ResultSetName– ResultSetTimeToLive

• Integer TotalHits• Records• Status (Status Code & Diagnostic)

CQL: Common Query Language

• Loosely based on CCL Search• Boolean & Proximity Operators• Index Sets & Indexes• Truncation Characters ‘*’, ‘#’ & ‘?’• Example:

dc.title=“harry potter” or bib1.isbn=123-456-78x

Explain Now Possible

• Not practical for classic Z39.50• List of supported Schemas• List of supported Indexes

SRU: Search and Retrieve with URL’s• SRW Without the SOAP Wrapper• Intended for Thin Clients• Adds ResponseSchema Parameter• Example

http://deimos.oclc.org/SRW/etdcat?query=nuclear&maxRecords=10

Outlook for SRW/SRU

• A solution looking for a problem?• Not likely to be quickly adopted by the

library community• Could show up first in other

communities: Geospatial, Biodiversity, OAI(?)

• Will be seen as a competitor with XML Query

Links

• http://www.loc.gov/z3950/agency/zing/zing.html

• http://staff.oclc.org/~levan/docs/RAC20020321-SRW.ppt

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