|Re: queries on queries in VIATRA [message #1752948 is a reply to message #1752926]
||Tue, 31 January 2017 08:19
| Zoltan Ujhelyi
Registered: July 2015
I hope I have understood your question correctly. If not, or the answer is not clear, feel free to ask for clarification.
If you are asking for how the language supports queries whose result set depends on other queries result sets, the query language provides support for that, similar to subqueries in SQL: you can write a pattern that describes the subquery, and then you can use the three kinds of 'find' constructs for composing the final result:: (1) positive pattern call constraints ('find'), (2) negative pattern call constraints ('neg find') and (3) aggregator values (such as 'count find' or 'sum find'). All these language elements take the match set of another pattern, and allow to write additional constraints to extend or limit the result set accordingly. Alternatively, you can think of this approach as a query defining a named database view that you can refer to from other queries. In such cases, the incremental engine of VIATRA manages the propagation of changes between the different patterns automatically.
Hope that helps,
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