Sound and Relaxed Behavioural Inheritance

Object-oriented (OO) inheritance establishes taxonomies of OO classes. Behavioural inheritance (BI), a strong version, emphasises substitutability: objects of child classes replace objects of their ascendant classes without any observable effect difference on the system. BI is related to data refinement, but refinement's constrictions rule out many useful OO subclassings. This paper revisits BI at the light of Z and the theory of data refinement. It studies existing solutions to this problem, criticises them, and proposes improved relaxations. The results are applicable to any OO language that supports design-by-contract (DbC). The paper's contributions include three novel BI relaxations supported by a mathematical model with proofs carried out in the Isabelle proof assistant, and an examination of BI in the DbC languages Eiffel, JML and Spec#

Object orientation without extending Z

The good news of this paper is that without extending Z, we can elegantly specify object-oriented systems, including encapsulation, inheritance and subtype polymorphism (dynamic dispatch). The bad news is that this specification style is rather different to normal Z specifications, more abstract and axiomatic, which means that it is not so well supported by current Z tools such as animators. It also enforces behavioural subtyping, unlike most object-oriented programming languages. This paper explains the proposed style, with examples, and discusses its advantages and disadvantages

An empirical study evaluating depth of inheritance on the maintainability of object-oriented software

This empirical research was undertaken as part of a multi-method programme of research to investigate unsupported claims made of object-oriented technology. A series of subject-based laboratory experiments, including an internal replication, tested the effect of inheritance depth on the maintainability of object-oriented software. Subjects were timed performing identical maintenance tasks on object-oriented software with a hierarchy of three levels of inheritance depth and equivalent object-based software with no inheritance. This was then replicated with more experienced subjects. In a second experiment of similar design, subjects were timed performing identical maintenance tasks on object-oriented software with a hierarchy of five levels of inheritance depth and the equivalent object-based software. The collected data showed that subjects maintaining object-oriented software with three levels of inheritance depth performed the maintenance tasks significantly quicker than those maintaining equivalent object-based software with no inheritance. In contrast, subjects maintaining the object-oriented software with five levels of inheritance depth took longer, on average, than the subjects maintaining the equivalent object-based software (although statistical significance was not obtained). Subjects' source code solutions and debriefing questionnaires provided some evidence suggesting subjects began to experience diffculties with the deeper inheritance hierarchy. It is not at all obvious that object-oriented software is going to be more maintainable in the long run. These findings are sufficiently important that attempts to verify the results should be made by independent researchers

Metamodel-based model conformance and multiview consistency checking

Model-driven development, using languages such as UML and BON, often makes use of multiple diagrams (e.g., class and sequence diagrams) when modeling systems. These diagrams, presenting different views of a system of interest, may be inconsistent. A metamodel provides a unifying framework in which to ensure and check consistency, while at the same time providing the means to distinguish between valid and invalid models, that is, conformance. Two formal specifications of the metamodel for an object-oriented modeling language are presented, and it is shown how to use these specifications for model conformance and multiview consistency checking. Comparisons are made in terms of completeness and the level of automation each provide for checking multiview consistency and model conformance. The lessons learned from applying formal techniques to the problems of metamodeling, model conformance, and multiview consistency checking are summarized

On the Selection of Optimal Index Configuration in OO Databases

An operation in object-oriented databases gives rise to the processing of a path. Several database operations may result into the same path. The authors address the problem of optimal index configuration for a single path. As it is shown an optimal index configuration for a path can be achieved by splitting the path into subpaths and by indexing each subpath with the optimal index organization. The authors present an algorithm which is able to select an optimal index configuration for a given path. The authors consider a limited number of existing indexing techniques (simple index, inherited index, nested inherited index, multi-index, and multi-inherited index) but the principles of the algorithm remain the same adding more indexing technique