1. CCS (Calculus of Communication Systems)
2. Terminologies
3. Operator Set
4. The Vending Machine Example

CCS (Calculus of communication systems)

• an algebra for specifying and reasoning about concurrent systems
• a way for precisely modeling concurrent systems and a powerful tool for the concurrent programming

Terminologies

• Agent: a component of the system with unique identity, which persists through time, and its own specified behavior. An agent may be atomic or composite.
• Action: also called event, which is either the interaction of an agent with its neighbors or an occurrence independently of them.
• Behavior: the set of events or actions an agent can perform. As for a system, it is its entire capability of communication
• Port: site on an agent through which it communicates with other agents
• Handshake: a set of indivisible acts through which agents communicate with each other, and experienced simultaneously by both participants.

• Representation: Usually the structure of an agent is represented graphically and its behavior is in equations. Here is an example.

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Operator Set

• Sequence operator ".": defines the sequence of actions an agent can take
• Selection operator "+": either of these actions can be undertaken nonderteministically
• Composition operator "|": defines the communications between agents and implies agents may proceed independently but may also interact through complementary ports
• Relaballing operator "[ / ]": a label overwrites another label
• Restriction operator "\{}": defines allowable actions within the system

Vending Machine Example

• Suppose there is a system composed of a vending machine and two boys who work together to get the candy bar.

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Behaviors of the machine and boys are defined as follows:

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Resultss

• Whether the restriction is applied or not will affect the system behavior.

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