Queries based on Concept Filters

Implement query objects similar to the ConQuer conceptual query language; see http://www.orm.net/queries.html for papers.

Queries are expressed as logical conditions over traversals of a fact graph, where facts are mapped to aspects of a relational schema.

Implementation Notes

• NOT(FEATURE(x)) should translate to x IS NULL if x is a one-to-one feature, or parent NOT IN (SELECT ...) if x is a one-to-many feature.