Join Constraints

Many application domains involve constraints that, at a conceptual modeling level, apply to one or more schema paths, each of which involves one or more conceptual joins (where the same conceptual object plays roles in two relationships). Popular information modeling approaches typically provide only weak support for such join constraints. This paper contrasts how join constraints are catered for in Object-Role Modeling (ORM), the Unified Modeling Language (UML), the Objectoriented Systems Model (OSM), and some popular versions of Entity-Relationship modeling (ER). Three main problems for rich support for join constraints are identified: disambiguation of schema paths; disambiguation of join types; and mapping of join constraints. To address these problems, some notational, metamodel, and mapping extensions are proposed.