Qualified Inheritance in Spatio-Temporal Databases

In a growing number of applications, different complementary views of real-world objects are needed. This is particularly true in spatial modelling - where the designer can propose different geometries for a given spatial object - or, in temporal modelling -where different life cycles can be defined on an object depending on the adopted point of view. A solution to provide multiple representations on objects is to offer a model supporting multiple instantiation, i.e. allowing real world entities to be instantiated in several classes. At the same time, object-oriented languages and object-oriented modelling have become common in computer science (C++ and Java for the former and UML (Rum.,97) for the latter). Hence, oriented-object properties as inheritance, polymorphism and dynamic binding are commonly used and their expressiveness quite naturally exploited. However, classical object-oriented models and languages onlyallow an implicit form of multiple instantiation among an inheritance hierarchy, i.e. an instance of a class is also a member of all its super-classes. In this paper we propose a solution to integrate classical object oriented mechanisms into models handling multiple instantiation and illustrate it on the conceptual model MADS. To achieve this, the dynamic binding mechanism was revisited, through the concept of scope of an instance (awareness of other instances), in order to manage the ambiguities induced by multiple instantiation. Last, providing an operational solution, a set of operators to modify the point of view of an object (determining which of its class instances is considered) and its scope is defined.