1 SWAD Europe Storage and Retrieval Workshop Dave Beckett

2 Overview Goals Discussion outcome Key issues

3 Goals Gather from implementors: –Techniques –Problems met Discuss –Storage models, schemas, experience –Aggregation, provenance –Test data for stores, queries –Implementing datatypes, RDFS, OWL

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

5 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

6 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

7 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

8 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.

9 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

10 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

11 Web APIs and Web Services Networked services Several tools provide WS APIs SOAP use REST architectural style preferred RDF Net API

12 Software APIs FAQ #1: What is the best software? [in my favourite language(s)] Healthy competition in APIs

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

14 Thanks See: Questions?