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Chapter♥ Copyright 2009 Digital Enterprise Research Institute. All rights reserved.
Digital Enterprise Research Institute www.deri.ie
Implementing Semantic Web applications:reference architecture and challenges
Benjamin Heitmann, Sheila Kinsella, Conor Hayes, and Stefan Decker
Workshop on Semantic Web Enabled Software Engineering 2009
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Introduction
Focus of Semantic Web research until now:benefits of Semantic Web technology
Less research on: costs, effort, challenges of Semantic Web technology
Result:estimating cost/benefit offset for Semantic Web technologies is difficultobstacle for uptake of Semantic Web technologies by real-world projects
Our contributions: identify main challenges and outline Software Engineering solutions
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Overview
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Empirical Analysis of 98 Semantic Web applicationsarchitectural analysis + app functionality questionnaire
Reference Architecture for Semantic Web applicationsMain challenges of implementing Semantic Web technologies
and their effect on an example applicationApproaches for mitigating the challenges
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Empirical analysis - Architectural
Goal: identify common functionality Result: components, allow comparison between apps98 papers about apps from SemWeb challenge 2003-2008 & Scripting for SemWeb challenge 2006-2008
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Reference Architecture for Semantic Web applications
Empirical basis: architectural analysis provides standard decomposition criteriaallows comparing of functionality
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Empirical analysis - Functionality
Goal: characterise capabilities of componentsResult: statistics about the range of variations for
each componentResults for 37 apps validated by authorsSurvey covers 27 properties in 7 areas of
functionality
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Empirical analysis - Functionality
Data Interface: data sources used (external/decentralised/evolving ?)Persistent Storage: Semantic Web standards supported (e.g. RDF, OWL, SPARQL ?)User Interface: generic/domain specificData Integration: manual/automaticSearch Service: structured/unstructured dataAuthoring: read-only/edit/create new dataCrawling: one-time/continuous
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Functionality Variations(examples)
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Implementation challenges (1)
integration service is very common (72%)expensive: 80% require manual intervention76% allow updating data after initial integrationReasons:
use of non-standard termsincorrect usage of vocabulariesmultiple URIs for the same objects and incorrect merging
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1. Integrating noisy and heterogeneous data
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Implementation challenges (2)
70% allow access or importing of external data 60% can export data or are reusable as sourceonly 1/3 allow creation of new dataReason: standards are just emerging:
Linked Data principles: 2006, ~8 years after RDF (1999)RDFa for embedding RDF in HTML: finalised 2008GRDDL for converting (X)HTML to RDF: finalised 2007SPARQL update: not finalisedRDF forms and RDF pushback: not finalised
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2. Missing or belated conventions and standards
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Implementation challenges (3)
components have different data models (majority)object oriented (92%), relational database, graph based
slow, non-native APIs between components
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3. Mismatch of data models and APIs between components:
4. Distribution of application logic across multiple components
Result of 3+4: higher maintenance costs, performance loss due to non-native API overhead
Logic included not just in code but queries, rules, formal vocabularies
58% using inferencing, 24% using queries
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Example Application: SIOC explorer
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3 - Mismatched data models: graph/relational/OOMismatched APIs: ruby<->java, SPARQL (slow)4 - distributed app logic: crawler, integration, primary app logic
1 - Integration: all data is RDF+SIOC, still 2 integration steps required2 - Unclear best practices: every SIOC exporter requires different crawling
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Mitigating the challenges (1)
72% implement integration, 3 components required
Delegating generic integration simplifies architectureDrawback: application specific integration may still be
necessary
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1. Delegating generic functionality to external providers
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Mitigating the challenges (2)
most apps in survey created on case-by-case basis:multiple librariesmultiple programming languages mismatch of native APIsdistributed application logic
provide frameworks / software factories to assemble and customise complete applications
provide generic data integrationimplement best practices and guidelinescentralise application logicallow app specific customisation
inspiration: Ruby on Rails, PHPCake, Django (Python), Struts (Java)
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2. Assembling applications from components:
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Summary
main challenges of implementing SemWeb techcost of integrating noisy or heterogeneous data
(non-RDF and RDF data)missing or belated standards and conventionsmismatch of data models and APIs between componentsdistribution of application logic across components
approaches to mitigate the challenges:delegate generic functionality to external servicessupport assembly of complete applications with
frameworksempirical foundation: analysis of 98 Semantic Web
applications
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