Modular Reasoning in the Presence of Event Subtyping

Abstract

Separating crosscutting concerns while preserving modular reasoning is challenging. Type-based interfaces (event types) separate modularized crosscutting concerns (observers) and traditional object-oriented concerns (subjects). Event types paired with event specifications have been shown to be effective in enabling modular reasoning about subjects and observers. Similar to class subtyping there are benefits to organizing event types into subtyping hierarchies. However, unrelated behaviors of observers and their arbitrary execution orders could cause unique, somewhat counterintuitive, reasoning challenges in the presence of event subtyping. These challenges threaten both tractability of reasoning and reuse of event types. This work makes three contributions. First, we pose and explain these challenges. Second, we propose an event-based calculus to show how these challenges can be overcome. Finally, we present modular reasoning rules of our technique, and show its applicability to other event-based techniques including join point types. AbstractSeparating crosscutting concerns while preserving modular reasoning is challenging. Type-based interfaces (event types) separate modularized crosscutting concerns (observers) and traditional object-oriented concerns (subjects). Event types paired with event specifications were shown to be effective in enabling modular reasoning about subjects and observers. Similar to class subtyping, organizing event types into subtyping hierarchies is beneficial. However, unrelated behaviors of observers and their arbitrary execution orders could cause unique, somewhat counterintuitive, reasoning challenges in the presence of event subtyping. These challenges threaten both tractability of reasoning and reuse of event types. This work makes three contributions. First, we pose and explain these challenges. Second, we propose an event-based calculus to show how these challenges can be overcome. Finally, we present modular reasoning rules of our technique and show its applicability to other event-based techniques.

Modular reasoning in the presence of event subtyping

“…Two translucid contracts are structurally similar if for each specification (program) expression in the assumes block of one, a possibly different specification (program) expression exists in the assumes block of the other at the same location. Ptolemy S 's structural similarity for the refining relation allows definition of Ptolemy S 's event specification inheritance, in [26], such that it statically guarantees the refining relation by combining translucid contracts of an event and its superevents in a subtyping hierarchy.…”

“…Ptolemy S 's semantics, in Appendices A and B, guarantees the conformance, using a combination of type checking and runtime assertion checking. Ptolemy S 's event specification inheritance [26], statically guarantees the refining relation and Ptolemy S 's dynamic semantics guarantees the non-decreasing relation. Figure 5 shows the interplay of conformance, refining and non-decreasing relations.…”

“…Consequently, for the refining relation, Ptolemy S 's specification inheritance [26] could be adapted to join point types, mostly through syntactic adaptations, to statically guarantee the refining relation between translucid contracts of a join point type and its super type.…”