Lifelines and messages in capsule-based sequence diagrams

A sequence diagram is a Unified Modeling Language (UML) diagram that illustrates the sequence of messages between capsules in an interaction. A sequence diagram consists of a group of capsules that are represented by lifelines, and the messages that they exchange over time during the interaction.

Capsule-based sequence diagrams show the sequence of messages that pass between capsules and that can affect possible state changes within the capsules. You can develop capsules, capsule parts, ports, protocols and events in a capsule owed sequence diagram. After you develop the structure of a system, you can use capsule-based sequence diagrams to represent the sequence of messages and the behavior of the system that you are modeling. Sequence diagrams describe the messages and events that are associated with protocols and the sequence that they occur in.

Capsule-based sequence diagrams are complex and can contain concurrent and distributed active architectural components. Capsules interact with their surroundings through one or more signal-based boundary objects called ports.

A port is a physical part of the implementation of a capsule that mediates the interaction of the capsule with the outside world; it is an object that implements a specific interface. Ports realize protocols, which define the valid flow of information (signals) between connected ports of capsules. Ports provide a mechanism for a capsule to export multiple different interfaces, each tailored to a specific role.

A capsule-based sequence diagram message is the representation of the sequence of communication that is sent and received through ports. You create capsule-based sequence diagram messages in the same way as a sequence diagram message. The messages originate from the sending port and their destination is the matching receiving port. Protocols are the type or contents of the message that the sending port sends and that the receiving port is expects to receive and interpret.


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