1.2.2 Statecharts Extensions to FSA

David Harel has added extensions to FSA to make it a practical and expressive formalism [4]. With those extensions, it becomes possible to specify the complete reactive behavior of a system in a model.

Figure 1.7: The statecharts meta-model in an Entity-Relationship diagram

The meta-model of statecharts is drawn in the ER diagram in Figure 1.7. Elements in the diagram are described below:

• The name Blob is used to distinguish hierarchical states in statecharts from states in FSA. Since hierarchy and orthogonal components are introduced in statecharts, the states may have inner structures and are known as blobs. A blob has a Name attribute.

• A Hyperedge connects two states and denotes a transition between them. A transition has an event property, and may or may not have properties guard and output. Those properties and their meanings are discussed later.

• A blob may consist of one or more orthogonal components. Each of them maintains a local current state. The Cartesian product of the current states of all the orthogonal components belonging to the same parent is equal to the current state of the parent state. An orthogonal component may have blobs inside it.

• Like FSA, every statecharts model has an initial state. Within every blob or orthogonal component there is also a default state.

The statecharts semantics has many variants. One popular semantics is David Harel's STATEMATE semantics [5]. Another one is the statecharts semantics described in the UML (Unified Modeling Language) [6]. These variants are not compatible with each other. There will be more discussion about the statecharts variants in the latter part of this thesis work.