Use Cases

Cases for extending XQuery

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EXQuery math module

by Jim Fuller, on 2009-03-27T13:00:12.07-07:00

  • eXist XML database:
    • util:random() xs:double
    • util:random($a as xs:integer) xs:integer
    • math:random() xs:double

  • MarkLogic XML database:
    • xdmp:random([$max as xs:unsignedLong])xs:unsignedLong as

  • Saxon XQuery and XSLT processor:
    • math:random(): Returns a somewhat random number between 0 and 1
    • random:random-sequence(1,$seed): Returns a set of random numbers based on an initial seed

random()With six potentially different functions, you begin to see how difficult it is to write compatible XQuery code when this much variability exists in extension function libraries to generate a random number.

util:randommath:randomThe three eXist XML database functions offer perhaps the least-optimal situation, as the relationship is unclear between and . I presume that this is concomitant with some refactoring or (common in open source development) to two functions created by two individuals. Worst, these two functions might represent some kind of versioning between old and new.

util:randomxs:integerxs:integerxs:doubleTo cap it all, eXist's function adds more diversity by accepting an seed argument and returning an (rather than the that the other two functions return).

random($max)xs:unsignedLong$maxMarkLogic defines a single function that returns a random, unsigned integer between 0 and a number up to 64 bits long. Its return type, being an , represents an unsigned integer between 0 and 18446744073709551615 (inclusive). The function optionally defines a maximum value by supplying a argument of the same type.

random()random()random()Saxon opts to support EXSLT which should be a good thing. However, because EXSLT currently has no context with XQuery, using the Saxon functions is somewhat confusing. The Saxon functions might be the best example of the considerably confusing situation across XQuery processor implementations of the function.

This combination of dissimilar and multiple namespaces with different functional signatures makes it impossible to create cross-platform run time XQuery applications, as most XQuery processors will choke during static analysis.

there is a lot of variability in math functions (just take a look at the random() function of eXist, MarkLogic, saxon ... I will review the random based functions. A Math module would be relatively straightforward to define and I think would represent 'low hanging' fruit in kicking off EXQuery.