1. A method for processing queries comprising: executing a query to generate a relation defined by a model clause specified in said query, said model clause specifying: one or more dimension columns of said relation, and a rule, wherein said rule comprises: a left-side expression, wherein said left-side expression includes one or more existential predicates, wherein each of said one or more existential predicates evaluates to a Boolean value and refers to at least one of said one or more dimension columns of said relation; and a right-side expression; wherein executing said query comprises evaluating said rule, wherein evaluating said rule includes performing an UPSERT operation to insert a row into said relation; and wherein the method is performed by one or more computer systems.
4. The method of claim 1 , wherein: said left-side expression further includes one or more qualified predicates, wherein each of said one or more qualified predicates generates a single value; wherein each of said one or more qualified predicates corresponds to one dimension column of said one or more dimension columns; said left-side expression defines a set of rows in said relation, wherein each row of said set of rows includes: each of said one or more dimension columns that corresponds to each of said one or more existential predicates; and each of said one or more dimension columns that corresponds to each of said one or more qualified predicates; and after evaluating said rule, said set of rows includes rows for all combinations of: each of said one or more dimension values for which each of said one or more existential predicates evaluates to a Boolean TRUE value; and each single value generated by each of said one or more qualified predicates.