Support of lists in PRD

Hello all,

This is to express my high-level opinion about the support of lists in 
PRD. Maybe we have a slot to discuss this during the F2F. I put this in 
itemized form to be more synthetic.

·       The notion of field typed as a list (or a collection) should 
exist.
·       For a list or a collection, it would be good to have indication 
about the cardinality (min and max), and the type of element. The 
information is very useful in authoring the rules.
·       PRD 1.0 should support simply operators like:
o       Length: take the length and write tests on it.
o       Contains: does the list contain such and such element?
o       Equality: Equality between 2 lists
o       Extraction of elements, like getFirst(), getElement(n), getLast().
·       Later on (for PRD 2.0?), we could use the list / collection as a 
support for aggregates, like “the average revenue of all the customers in 
the list”, and in the action part have a construct to loop on the elements 
of the lists.

Every serious data model or object model have lists and collections, so 
PRD should definitely support the lists / collections, with the simple 
operations described above.

Changhai

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