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SRU: An overview of the SRU protocol and how it can be used to

facilitate Web Service-based search

Monica Duke (Software Developer)

The British Library, 2nd June 2009

                                                             

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SRU: in a nutshell

• Web Service for Search and Retrieval• Search protocol

– Client sends message

– Server processes message, sends response

– Query languageSyntax for query parameters

                                                             

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History

• Derived from Z39.50• Brought over most useful bits, in

simplified format• Lower implementation barrier

                                                             

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SRU Timeline

• Version 1.0 (experimental) Nov 2002• Version 1.1 (stable) Feb 2004• Version 1.2 (latest) 2006/7• 1.2

– Organizational Changes (rebranding)– Technical Changes

• Standardization sought 2007

                                                             

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Standardization– Both Industry and Academia participate– Neutral ground for merging competing de

facto standards

• Process– Open Discussion– Formation of OASIS Technical Committee– Discussion, Ballot– Leading to SRU 2.0– http://www.dlib.org/dlib/january09/denenberg/01denenberg.html

                                                             

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What is a Web Service?

• Facilitates communication to a networked application– Client requests something – Server carries out the request and reports success or

failure– Responses and requests (sometimes) are encoded in

XML• Programmers embed calls to a web service

as a part of a useful local application– Query a online database– Receive news updates– Receive stock quotations

                                                             

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What is REST?

• REpresentational State Transfer – A design philosophy not a protocol– The fundamental concept behind the web– Each URL/URI is a unique state transferred from

server to client

• Characteristics of REST-ful web services:– Always over HTTP– Request: Form a URL + query string

http://myrest.com/?query=cat&operation=search

– Response: Comes back in XML

                                                             

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REST vs SOAP/XML-RPC

Eric Lease Morgan classifies web services:SOAP-ful Web Services

– More complicated; but potentially more robust than REST

– Can use any sort of transport mechanism, email; SSH, telnet

– Encoded using the SOAP XML wrapper – W3C standard for web services

– Example – The Google API (incorporate Google’s search results into your own program)

REST-ful Web Services– Serve up as arbitrary application defined XML only

– Transported via HTTP requests only

                                                             

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SRU: SOAP and REST• SOAP-ful version: SRW

Search defined using XMLMore complex parameters possible

• REST-ful version: SRU

• Since 1.2, both rebranded as SRU to reflect actual usage

SRW SRU via SOAP

                                                             

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Basic SRU server

• Understands queries written in CQL (Common Query Language)

• Queries sent to an SRU server as a URL parameter

• Receive a structured XML response with search results

• Take this Result and…Format it for your users using XSLTMore processing- do something else with it

                                                             

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SRU: Three Basic Operations

Explain (please describe yourself)

Search/Retrieve (search, sort, fetch)

Scan (browse)

                                                             

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SRU search parameters

Base URL: identifies the serviceParameters:

QueryrecordSchemamaximumRecordsstartRecord

                                                             

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Example search retrieve

http://example.org/?operation=searchRetrieve&query=dog&version=1.2

                                                             

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Example response<searchRetrieveResponse> <version>1.1</version><numberOfRecords>3</numberOfRecords> <records> <record> <recordSchema>info:srw/schema/1/dc-v1.1</recordSchema><recordPacking>xml</recordPacking> <recordData> <dc> <title>The bottom dog</title>

<identifier>http://example.org/bottom.html</identifier> </dc> </recordData>

</record> (next record….)

                                                             

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XSLT for formatting

• Send an xslt parameter• Response is processed • Results are presented in diferent

formats

SRU in Use: OAI

OAI HarvestersOAI Data Providers

SRU Server

Make Data Available

Harvest and Maintain Updated

Indexes of Data

Search and Present Data to Users

SRU in Use: European Library

                                                             

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Competing standards

• OpenSearch/A9part of the OASIS standardizationSimpler keyword searching

• OpenURL

                                                             

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Why choose SRU?

• Part of the standardization process in OASIS

• Allows control over query and results• Library community• Open questions

– Will standardization influence uptake?– Will other approaches join the effort?

                                                             

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Repositories and SRU

• Individually?• Through aggregation…

                                                             

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Where to find out more• Official page

– http://www.loc.gov/standards/sru/

• Mailing List (Implementor's ListServ)• Bibliography

– http://www.loc.gov/standards/sru/background/bibliography.html

– Introduction, SRU and OAI, SRU and The European Library

                                                             

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Acknowledgements

• Rob Sanderson• Kevin Reiss (2005)• A Rest-ful Web Services Approach to Library Federated Search using SRU