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 –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 Undermining XQuery with something better? –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 Closed world Client/server Distributed databases Query/answer Active databases QBE interfaces NEW data management 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

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