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With the addition of higher order functions and the discussion around adding map values, SequenceTypes are becoming more and more complex - especially when building complex data structures from these types of values. We should add a type alias (or type definition) facility to allow complex SequenceType to be referred to with simple QNames, and to allow the definition of recursive types: declare type-alias my:transform-function as function($nodes as node()*, $params as map(*)) as item()*;
We discussed this in meeting #523 and decided this is a "may" requirement. <quote> Q2.9.17 Bugzilla Bug 17602, [XQ31ReqUC] Type alias / define See http://www.w3.org/Bugs/Public/show_bug.cgi?id=17602 may (for maps) </quote>
This bug has been redirected to the XQuery 3.1 document, as it has been accepted as a MAY requirement.
In their teleconference of 2014-04-22, the Working Group decided that this MAY requirement would not be satisfied in the XQuery 3.1 timeframe. As a consequence, I am marking the bug RESOLVED/LATER.
In their teleconference of 2014-04-22, the Working Group decided that this MAY requirement would be reconsidered for any future version of XQuery, should such future version materialize. As a consequence, I am recategorizing this bug as Requirements for Future Versions.
See http://dev.saxonica.com/blog/mike/2016/09/tuple-types-and-type-aliases.html for a Saxon extension designed to meet this requirement