z39.50 as a web service
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Z39.50 as a Web Service. Ralph LeVan Research 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. - PowerPoint PPT PresentationTRANSCRIPT
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: MetaSearch, 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/SRW-RAC20030814.ppt
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