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# Semantics
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# Constraint Programming model representation in NDL
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*2018-10-12*
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A Prolog-like knowledge base containing only binary and unary facts. The only allowed constants are integers.
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# Syntax
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## Features
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Prolog expressed with s-expressions, e.g.
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Every model consists of:
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* variables indexed by tuples of integers (mimicking multidimensional arrays)
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* constraints defined on the pairs of variables
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* constants:
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* integers: may be used as ranges boundaries
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* ranges: may be used as domains or index sets for variables
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```
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(unary-fact 1)
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(unary-fact 2)
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(binary-fact 1 2)
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(binary-fact 2 1)
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```
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## Limitations
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* domains have to be ranges (no holes)
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## Examples
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# Queries
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The SWI-Prolog based prototype is available in the `noodle-prolog` directory.
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There is one basic example available for now.
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To run it, write from the `noodle-prolog` directory:
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Similarly to Prolog, query is a conjunction of atoms:
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```
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((unary-fact X) (binary-fact 1 X))
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./run_example.sh nqueens
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```
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As in Prolog, user can use both constants and variables.
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The only difference from Prolog is that there should be two ways of executing the query:
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* deterministic - the same as in Prolog; should be able to generate all the possible results to the query in a repeatable way
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* indeterministic - generating one random result to the query |
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\ No newline at end of file |
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Then you can check `examples/nqueens.ndl` to see ndl model of the basic 8-queens problem.# |
