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Rick JELLIFFE wrote: > > > Mike.Champion@S... wrote: > > > I can think of a couple of arguments. > > First, In the world of query languages, it's clear to me that > > procedural approaches don't scale well -- you want an optimizer to > > figure out the best way to "just do it" given all it knows about the > > data, indexes, storage structures, etc. > > I don't think that it has been established that what might be clear for > relational data (tables) is also true for XML (trees). > > I can see that if one were accessing tree data as if it were a > hierarchy of records and one had to explicitly nominate the records to > be taken (i.e., if each subtree had to be grown or culled) then some > declarative model would be useful. But I don't think that is how XML is > used: One starts with the fact of a tree in which the most interested > data is already contained in nice branches (rather like pre-indexing?); > if one starts with a graph-of-records model then there is no natural > boundary. > > In other words, for relational data, data is grouped either by being in > a records or by keys. In XML data, it is groups by elements, by path > expressions or by keys. That additional second stage (being able to > express relations by constant paths along a tree) is declarative, and I > think it changes the boundaries for querying to an extent that saying > "declarative scales; procedural doesn't" because even procedural > queries will have significant declarative components. > > Rick Jelliffe
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