UML 2.0 Sequence Diagram's Semantics

Scenario languages are widely used in software development. Typical usage scenarios, forbidden behaviors, test cases and many more aspects can be depicted with graphical scenarios. Scenario languages were introduced into the Unified Modeling Language (UML) under the name of Sequence Diagrams. The 2.0 version of UML changed Sequence Diagrams significantly, the expressiveness of the language was highly increased.

The following figure depicts some of the elements of Sequence Diagrams:

The OMG specification presents a high-level semantics for Sequence Diagrams, however, the due to the complexity of the language (parallel executions, choices, infinite loops, use of modalities and negation, etc.) several open questions remain. Many formal semantics were proposed in the recent years for Sequence Diagrams. But as the language itself contains a number of so called semantic variation points and as the different formal semantics use Sequence Diagrams for different purposes (describing high-level specifications or test cases, defining a set of valid traces or verifying actual traces, etc.) there are several choices when interpreting Sequence Diagrams.

The many meanings of UML 2 Sequence Diagrams: a survey

Paper: Z. Micskei and H. Waeselynck: The many meanings of UML 2 Sequence Diagrams: a survey, Software and Systems Modeling, Vol. 10, Num. 4, pp. 489-514, Springer, 2011. DOI:10.1007/s10270-010-0157-9

This paper collects and categorizes the semantic choices in the language, surveys the formal semantics proposed for Sequence Diagrams, and presents how these approaches handle the various semantic choices.

The semantic choices are presented on diagrams inspired by feature models, in this way the different options for a given semantic question can be more clearly summarized. The following figure illustrates the choice whether an interaction represents complete or partial traces.

UML 2.0 Sequence Diagram's Semantics -- Technical report

Report: Z. Micskei and H. Waeselynck: A survey of UML 2.0 sequence diagrams' semantics, LAAS Technical Report, August 2008.

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This technical report contains an older, slightly different approach for categorizing the choices and issues. However, it contains more information about the syntax and semantics of UML 2 Sequence Diagrams, and presents several proposed formal semantics in more details with the help of sketching the recommended formal semantics of an example diagram.

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