Publications of Anna Formica

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IASI Research Report n. 441  (Previous    Next)  

Anna Formica, Michele Missikoff

Analysis of the inheritance process in strongly typed OODB systems

ABSTRACT
In this paper, the problem of designing correct Object-Oriented Database (OODB) schemas in strongly typed systems is adressed. Schema correctness is a basic requirement for data integrity. OODB schemas are organised according to a type (or class) hierarchy which has, traditionally, two imports. An engineering import, for which supertypes are used to factorize the characteristics common to subtypes, in order to enhance compactness and reuse (inheritance hierarchy). A conceptual import, for which types in hierarchy belong to a generalization/specialization relationship (subtyping hierarchy). In the proposed approach, the correctness of a schema is related to the integration of the two above aspects: inheritance must comply with subtyping. Our work starts from the well known type theory of Cardelli, accepted by a significant number of strongly typed OODB systems, and analyses the relationships between the notions of subtyping and inheritance in this frame. In the paper, we show that a "pure" inheritance process, i.e., one that considers the rewriting of subtypes with inherited features, is not able to process all correct schemas because of the existence of a subclass of recursive schemas for which the inheritance process always terminates, referred to as Inheritance Process-safe schemas, are formally characterised by using a graph-theoretic approach.
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