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XML (with a bias towards query language issues) A boring research topic? A new frontier? A means to keep standards people busy? Prepared by S. Abiteboul and J. Widom XML • Rapidly adopted by industry • A format for exchange of small/medium pieces of data? – Yes – But when archived, grows to large volumes • Also a data model? – Yes, for all kinds of data – From unstructured documents to collections of structured data – Warning: this is not the relational world! • Permissive typing, full-text search, … The database community should be very involved, perhaps very concerned Some XML Issues • Storage of XML – Native vs. XML-relational • Lesson from OODB: it’s not only a technical issue but a business one • Situation is different: more $ involved – Efficient representation, compression – Key issue: interface • DOM, SAX, query language, DB-like API, … • Revisiting old topics – – – – – Database design Integrity constraints Concurrency control Access control Etc. All topics are under active investigation, sometimes reinventing the wheel Universal Query Language for XML • Problems with XQuery – – – • Undermining XQuery with something better? – – • Focus on complex queries; really need simple filters + IR-style search Too complex, too ambitious, lack of underlying paradigm, too much politics! Too broad spectrum of applications? From documents to data Personal viewpoint: Small core OQL-like + functional plug-ins Too late? We need a standard now! What about updates, standing queries, deltas, constraints, …? This direction has been mostly deactivated by XQuery Scientific: Is Xquery good or bad from a scientific viewpoint? Politics: Should we push for XQuery? Back to Basics: Query Optimization • For subsets of the language • The tree structure is definitely a new ball game – New index structures – New cost models – New everything • Depends on storage – Relational, native, others • Revisit old problems – Distributed query processing – View maintenance All topics are under active investigation (but more effort on distribution wouldn’t hurt) Back to Basics: Foundations • Lots of work on semistructured data – First-order logic and relational languages: strong – OQL/functional languages: reasonable – Full-text search: messy • Significant issue: typing – Much more complex than in relational world – Not settled (XML Schema, tree automata, …) – Query type-checking, type inferencing, update consistency • Very active area – People from database theory, functional programming, automata theory, … All topics already active, not simple, require more work The Real Frontier (The World is Changing) OLD data management NEW data management • • • • • • • • • • • Closed world Client/server Distributed databases Query/answer • Active databases • QBE interfaces Openness P2P applications Web-scale data Subscription queries Queries over streams ADB + Web services New interfaces Research should focus on the new issues rather than on traditional processing of single-site XML data Beyond XML: semantic Web Discussion