Transverse Activities: Abstractions in Object-Oriented Programming

A transverse activity is an activity executed by several objects in some combination. The activity is described as a single unit, separately from the descriptions of the participating objects. A transverse activity is described and executed by using the usual object{centric actions, i.e. the methods of the objects, and is seen as a natural supplement to the description of the cooperation of active objects. Transverse activities support the modeling of our conceptual understanding of combined activities. Our conceptual understanding not only includes the recognition of usual components but also the recognition of activities combined from the individual actions of such components. We are used to recognize components as phenomena, but transverse activities are phenomena also and these activities may be classiied, specialized, and aggregated, i.e. abstraction in this sense is possible also for such activities. The description of a transverse activity must at least include a listing of the components participating in the activity and a listing of the sequence of actions making up the combined directive of the activity. In the specialization or aggregation of activities by means of other activities both the participants and the directive can be included in these forms of abstraction to support the underlying intention of transverse activities. Usual language mechanisms such as class, object etc. in various forms are used to model phenomena and concepts. A ongoing revision and extension of such usual object{oriented language mechanisms is necessary to be able to model, directly and naturally, additional diierentiating elements of conceptual understanding, such as e.g. transverse activities. Transverse activities are illustrated and motivated by means of several minor fragments of a complex example and an conceptual understanding of transverse activities is outlined. Language mechanisms supporting the classiication, specialization, and aggregation of transverse activities is deened by means of special activity{classes and {objects. Various possibilities for adding new and powerful features as part of such mechanisms are discussed. The meaning of the execution of activity{objects in relation to the execution of the components involved in the activity is deened in terms of interleaved execution.