Part-whole statecharts for the explicit Representation of compound behaviours

Although very effective, the adoption of Statecharts in objectoriented software development methods poses many problems, since their way to compose behavioral abstractions can be framed in the general context of implicit composition. In particular, the need to embed references from one behavioral description to other ones has mayor drawbacks since the description of a single entity behaviour is not self-contained, and the global behaviour results implicitly defined by following references from one entity to the other. In other words, both single and global behaviors are difficult to understand, modify and reuse. The paper proposes to overcome most of such problems by adopting Part-Whole Statecharts, whose primary policy for controlling complexity strictly enforces distinct layers for wholes and their parts. Since wholes may become parts of other aggregations, a recursive syntax and semantics can be given straight for wardly.