This paper proposes an extension to the Object-Role Modeling approach to support formal declaration of dynamic rules. Dynamic rules differ from static rules by pertaining to properties of state transitions, rather than to the states themselves. In this paper, application of dynamic rules is restricted to so-called single-step transactions, with an old state (the input of the transaction) and a new state (the direct result of that transaction). Such restricted rules are easier to formulate (and enforce) than a constraint applying historically over all possible states. In our approach, dynamic rules specify an elementary transaction type indicating which kind of object or fact is being added, deleted or updated, and (optionally) pre-conditions relevant to the transaction, followed by a condition stating the properties of the new state, including the relation between the new state and the old state. These dynamic rules are formulated in a syntax designed to be easily validated by non-technical domain experts.

This paper contrasts two different approaches to designing relational databases that are free of redundancy. The Object-Role Modeling (ORM) approach captures semantics in terms of atomic (elementary or existential) fact types, before grouping the fact types into relation schemes. Normalization by decomposition instead focuses on “non0loss decomposition” to various, and progressively more refined, “normal forms”. Traditionally, non0loss decomposition of a relation requires decomposition into smaller relations that, upon natural join, yield the exact original population. Non-loss decomposition of a table scheme (or relation variable) requires that the decomposition of all possible populations of the relation scheme is reversible in this way. This paper shows that the dependency requirement for “all possible populations” is too restrictive for definitions of multi-valued and join dependencies over relation schemes. By exploiting ORM modeling heuristics, the authors offer new definitions of these data dependencies and non-loss decomposition, to enable these concepts to be addressed at a truly semantic level.

This paper proposes extensions to the Object-Role Modeling approach to support schema transformations that eliminate unneeded columns that may arise from standard relational mapping procedures. A "unique where true" variant of the external uniqueness constraint is introduced to allow roles spanned by such constraints to occur in unary fact types. This constraint is exploited to enable graphic portrayal of a new corollary to a schema transformation pattern that occurs in many business domains. An alternative transformation is introduced to optimize the same pattern, and then generalized to cater for more complex cases. The relational mapping algorithm is extended to cater for the new results, with the option of retaining the original patterns for conceptual discussion, with the transforms being applied internally in a preprocessing phase. The procedures are being implemented in NORMA, an open-source tool supporting the ORM 2 version of fact-oriented modeling.

No abstract

No abstract