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Development of Services in the Fedora Service Framework. by Gert Schmeltz Pedersen Development of Services in the Fedora Service Framework. Contents The Fedora Service Framework The Fedora Generic Search Service Considerations about a Peer-to-Peer Service for Fedora

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Development of services in the fedora service framework l.jpg

Development of Services in the Fedora Service Framework

by Gert Schmeltz Pedersen

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Development of Services in the Fedora Service Framework

  • Contents

    • The Fedora Service Framework

    • The Fedora Generic Search Service

    • Considerations about a Peer-to-Peer Service for Fedora

    • Conclusion

The fedora service framework l.jpg
The Fedora Service Framework

  • Services are stand-alone web applications that run independently of the Fedora repository

  • Two main benefits to the service framework approach:

    • allows new functionality to be added as atomic, modular services that can interact with Fedora repositories, yet not be part of the repository,

    • makes co-development of new services for Fedora easier since each service can be independently developed and plugged into the framework.

Flexible Extensible Digital Object Repository Architecture

• Powerful digital object model

• Extensible metadata management

• Expressive inter-object relationships

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The Fedora Service Framework

  • Fedora Object XML (FOXML) is a simple XML format that directly expresses the Fedora digital object model

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Development of Services in the Fedora Service Framework

  • The Fedora Generic Search Service

    • Background

      • The DEF-XWS project

      • Zebra at work

      • Lucene in action

    • Approach and requirements

    • Current prototype (fedoragsearch)

    • Architectural snapshots

    • Configuration and customization

    • Further work

    • The work is funded by DEFF, Denmark's Electronic Research Library.

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Open Archives Initiative Data Providers














Web UI


Web UI


DEF Portal User









Full set

Full text retrieval

Zebra server







DEF-XWS Eprints User

Batch ingest

Web UI



Fedora server


Web UI



DEF-XWS Eprints User





AppXYZ User

Sub set





Background - DEF-XWS Eprints

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Background - DEF-XWS Eprints

  • Purpose achieved

    • Fedora hands-on and experience

    • web services hands-on and experience

    • DEF-XWS Eprints available from web services



      • and to applications combining many web services

  • Lesson

    • Do not override field search,

    • provide generic search service instead ...

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Zebra at work


  • Zebra is provided as open source by Index Data.

  • Written in portable C, so it runs on most Unix-like systems as well as Windows.

  • Modules zebraidx and zebrasrv

  • Searching supports a combination of boolean queries, relevance-ranking, truncation, masking, full regular expression matching and "approximate matching" (eg. spelling mistakes).

  • Z39.50 protocol support, recently also SRW/SRU and CQL

  • Configurable to understand many input formats... SGML, XML, ISO2709 (MARC), raw text.

  • Arbitrarily complex records.

  • Robust updating - records can be added and deleted “on the fly”.

  • Very large databases: logical files can be automatically partitioned over multiple disks.

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”Lucene in Action”

Figure 1.5 A typical application integration with Lucene

dc.title:"Information retrieval" AND




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Approach and Requirements

  • Do iterations of requirements analysis and prototype development

  • allow various indexing-and-search engines to be configured or plugged in, initially Lucene and Zebra

  • implement as a webapp within the Fedora Service Framework

  • allow indexing of, and search in, all information in FOXML records for FedoraObjects, including full texts in datastreams and disseminator results

  • define interface for a set of operations, provide REST and SOAP access

  • basic operations:

    • updateIndex - indexing the contents of the Fedora repository

    • gfindObjects - search similar to Fedora findObjects

  • secondary operations:

    • browseIndex - browsing terms in a given index.

    • getRepositoryInfo - describing the properties of a repository

    • getIndexInfo - describing the properties of an index

  • allow multiple repositories to be indexed in one and the same index

  • allow multiple indexes to be generated from one repository

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Current prototype - updateIndex

  • <foxml:digitalObject … PID="demo:21">

  • <foxml:objectProperties>

  • <foxml:property NAME="" VALUE="FedoraObject"/>

  • <foxml:property NAME="info:fedora/fedora-system:def/model#state" VALUE="Active"/>

  • <foxml:property NAME="info:fedora/fedora-system:def/model#label" VALUE="Sample Document Object (FO to PDF)"/>

  • <foxml:property NAME="info:fedora/fedora-system:def/model#contentModel" VALUE="FO_TO_PDFDOC"/>

  • </foxml:objectProperties>

  • <foxml:datastream ID="DC" STATE="A" CONTROL_GROUP="X" VERSIONABLE="true">

  • <foxml:datastreamVersion ID="DC1.0" LABEL="Dublin Core for the Document object" CREATED="2006-05-16T10:23:48.376Z" MIMETYPE="text/xml" SIZE="606">

  • <foxml:xmlContent>

  • <oai_dc:dc xmlns:oai_dc="" xmlns:dc="">

  • <dc:title>Advanced FO Sample from Apache FOP Distribution</dc:title>

  • <dc:creator>Apache Group</dc:creator>

  • </oai_dc:dc>

  • </foxml:xmlContent>

  • </foxml:datastreamVersion>

  • </foxml:datastream>

  • </foxml:digitalObject>


  • <IndexDocument … >

  • <IndexField IFname="PID“ … >demo:21</IndexField>

  • <IndexField IFname="property.type“ … >FedoraObject</IndexField>

  • <IndexField IFname="property.state“ … >Active</IndexField>

  • <IndexField IFname="property.contentModel“ … >FO_TO_PDFDOC</IndexField>

  • <IndexField IFname="dc.title">Advanced FO Sample …</IndexField>

  • <IndexField IFname="dc.creator">Apache Group</IndexField>

  • <IndexField index="TOKENIZED" dsId="DS1" IFname="DS1.text"/>

  • </IndexDocument>

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Architectural snapshots - basic - fedoragsearch

  • Contents

    • Lucene

    • Zebra

    • fedoragsearch

      • REST demo

      • architecture

      • installation and configuration

      • further customizations

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Architectural snapshots - indexing - many-to-many

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Configuration and customization

  • Configuration examples:


  • - soapBase = http://HOSTPORT/fedoragsearch/services

  • - repositoryNames = REPOSNAMES

  • - indexNames = INDEXNAMES

  • mimeTypes = MIMETYPES


  • - operationsImpl = dk.defxws.fgslucene.OperationsImpl

  • defaultQueryFields = dc.description dc.title


  • - soapBase = http://FEDORAHOSTPORT/fedora/services

  • - fedoraObjectDir = FEDORAOBJECTDIR

  • Customization examples:

  • demoFoxmlToLucene.xslt

    • <IndexField IFname="DS2.text" dsId="DS2" index="TOKENIZED" store="YES" termVector="NO">

    • </IndexField>

  • demoGfindObjectsToHtml.xslt

    • <script …AJAX-script … />

    • <h2>gfindObjects</h2>

    • <form method="get" action="rest">

  • Implement plugin for XyzEngine

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Further work

  • From prototype to production version

    • Clean up

    • Give access

    • Make better Exceptions and error messages

    • Handle XACML

    • Notification mechanism

    • javaDoc

    • Junit test cases

    • Test on various platforms

    • Documentation

    • Ensuring that we obtain the same high quality as the Fedora code itself has

  • Takeover by core development team

  • Contributions from Fedora community

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Development of Services in the Fedora Service Framework

  • Considerationsabout a Peer-to-Peer Service for Fedora

    • The Background: Alvis utilization activities

    • The EU project: Alvis - Superpeer Semantic Search Engine

    • Analysis of alternatives

    • Design of a Peer-to-Peer service for Fedora

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The Background:Alvis utilization activities

  • The Alvis project is developing an open source prototype of a distributed, semantic-based search engine.

  • An important consideration in the Alvis project has been how to utilize Alvis results in the Digital Library context.

  • Therefore, a test case is established with the purpose to utilize Alvis results in the context of the Fedora repository system

    • (the assumption is that the experience and some principles will be applicable to other digital library systems)

  • The test plan for this test case has the following steps:

    • Analysis

      • Alternative 1: a document enrichment service

      • Alternative 2: a peer-to-peer service

    • Design of a peer-to-peer service for Fedora, so that Fedora may act as an Alvis superpeer

    • Involving the Fedora developer and user community

    • Implementation of the service

    • Evaluation of uses of the service

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The Alvis EU project

  • The initial tasks

  • research in the design, use and interoperability of topic-specific search engines

  • development of an open-source prototype of a distributed, semantic-based search engine

  • building on content through automatic analysis of free text

  • advancing peer-to-peer technology

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The Alvis EU project

  • Peer-to-Peer service

  • network-wide search

  • input system can include a crawler, an RSS reader, XML database extraction, etc.

  • document system does routine processing on documents prior to entry to the runtime system, such as tagging named entities.

  • maintenance system does processing at the full document collection level to update linguistic and semantic resources used in the document system.

  • superpeer runs the search engine at a node and provides the user interface. This represents an individual, possibly topic specific search engine.

  • p2p system provides a network-wide interface to a set of individual search engines using P2P.

  • Document enrichment service

  • semi-automatic tagging with semantic knowledge

  • Peer-to-peer (From Wikipedia, the free encyclopedia)

  • A peer-to-peer (or P2P) computer network is a network that relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers.

  • The P2P overlay network consists of all the participating peers as its nodes and has links between any two nodes that know each other

  • Structured P2P networks overcome the limitations of unstructured networks by maintaining a Distributed Hash Table (DHT) and by allowing each peer to be responsible for a specific part of the content in the network.

Analysis document enrichment service l.jpg

















Linguistic format

Relevance format

Acquisition format






Chinese contribution

Crawler, linguistic analysis and relevance analysis

Analysis: Document enrichment service

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Analysis: Document enrichment service

  • Functionality as a Fedora service

  • Topic-specific crawling based on subject hierarchies

  • Natural language analysis of content

  • Entity recognition

  • Classification of content

  • Addition of synonyms

  • Topic specific scores for customised rankings

  • Too many partners/modules/subsystems involved

  • Usages of enrichment not clarified

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Analysis: Peer-to-Peer service

  • The initial vision

  • A set of heterogeneous servers connected into a search network

  • Each one is wrapped suitably, so as to act as Alvis Search Peers

  • In this view, Fedora repositories may be wrapped as well.


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Design: alvisp2p service

  • The alvisp2p service shall implement the interfaces IndexingQuery and Retrieval for interacting with the P2P system, and

  • implement the necessary operations for interacting with the core Fedora repository service.

  • Seen from the ALVIS view point we will then have a thin superpeer,

  • seen from the Fedora view point we will have a Peer-to-Peer service.

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Development of Services in the Fedora Service Framework

  • Conclusion

    • Two examples of services illustrating the issues in developing services for the Fedora Service Framework

      • Interaction with Fedora

      • Reuse from Fedora

      • Security

    • A promising development approach for Fedora

    • Promising in general for Digital Object Repository Systems in Digital Libraries?

      Thank you

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For more information

  • A Peer-to-Peer Architecture for Information Retrieval Across Digital Library Collections, Technical report LSIR-REPORT-2006-005, March 2006.

  • Report on abstract model and P2P protocols, ALVIS Deliverable 4.1, 2006.

  • Beyond term indexing: A P2P framework for Web information retrieval, submitted to thr Informatica journal, December 2005.

  • Building a peer-to-peer full-text Web search engine with highly discriminative keys, Technical report LSIR-REPORT-2005-011, November 2005.

  • Using a layered Markov model for distributed web rank computation, ICDCS 2005, Columbus, Ohio, U.S.A., June 2005.

  • Towards A Common Framework for Peer-to-Peer Web Retrieval, Book Chapter of From Integrated Publication and Information Systems to Virtual Information and Knowledge Environments, EJN-Festschrift, Matthias Hemmje Ed., Springer LNCS 3379, November 2004.

  • An Architecture for Peer-to-Peer Information Retrieval, in 27th Annual International ACM SIGIR Conference (SIGIR 2004), Workshop on Peer-to-Peer Information Retrieval, July, 2004.

  • A Query-Adaptive Partial Distributed Hash Table for Peer-to-Peer Systems", in InternationalWorkshop on Peer-to-Peer Computing & DataBases (P2P&DB 2004), Crete, Greece, March 2004.

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alvisp2p service scenario

Logon to network

Receive local query

Deliver local hit list

Publish document list

Publish index

Receive global hit list

Publish query

Logoff from network