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SWAD Europe Storage and Retrieval Workshop

Dave Beckett

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Overview

• Goals• Discussion outcome• Key issues

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Goals

• Gather from implementors:– Techniques– Problems met

• Discuss– Storage models, schemas, experience– Aggregation, provenance– Test data for stores, queries– Implementing datatypes, RDFS, OWL

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Storage Issues

• RDBMs or not• When to optimise from relational?• Scalability - today ~40M triples• Planning for 10x increase• Inference and text-searching

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Retrieval Issues - APIs

• Language APIs– Some languages have many RDF APIs

(Good thing / bad thing)

• Cross-language APIs– like DOM, IDL for RDF– That might be a query language

• Networked APIs

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Retrieval Issues - Contexts

• Not all software has support• Two main uses of context seen:

– Source URI (where triples came from)– Sub-graph identifier (modelID)

• Others:– Statement identifier (not reification)– Internal identifier

• Little query language support

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Lessons from implementing OWL, RDFS• RDFS easy except for 2 items• User-driven datatype support• XSD via third-party libraries• Interest in understanding OWL

layering• “OWL Tiny” the most implemented

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OWL Tiny

“OWL Tiny is the subset of OWL Lite that contains property characteristics and identity relations from OWL Lite. It is the part of OWL that cannot produce conflicts.”Steve Harris,University of Southampton.

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Retrieval and Querying

• Retrieval by query• Several QLs in similar SQLish style• RDQL, RQL, SeRQL, more…• SQL familiarity is a good thing• Felt now is time to standardise

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Query language standardising

• Conjunctive query with constraints• Maybe: +contexts, optionals• Not now: updates• Multiple other QL requirements• RDF graphs in and out useful• Path based querying• Query across graphs

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Web APIs and Web Services

• Networked services• Several tools provide WS APIs• SOAP use• REST architectural style preferred• RDF Net API

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Software APIs

• FAQ #1:What is the best software?[in my favourite language(s)]

• Healthy competition in APIs

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Summary

• Stores exist in substantial sizes• Please standardise a QL soon• Contexts are needed but messy

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Thanks

See: http://www.w3.org/2001/sw/Europe/ Questions?