Message sequence chart

<h2 id="history">History</h2>
<p>The first version of the MSC standard was released on March 12, 1993.
</p><p>The 1996 version added references, ordering and <a href="/facts/Inline_expansion/jhQsJwLX">inlining</a> expressions concepts, and introduced HMSC<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> (High-level Message Sequence Charts), which are the way of expressing a sequence of MSCs.
</p><p>The MSC 2000 version<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> added object orientation, refined the use of data and time in diagrams, and added the concept of remote method calls.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>Latest version has been published in February 2011.
</p>
<h2 id="symbols-in-msc">Symbols in MSC</h2>
<p>The existing symbols are:
</p>
<ul><li>MSC head, lifeline, and end: a vertical line with a box at the top, and a box or a cross at the bottom.</li>
<li>Instance creation: horizontal dashed arrow to the newly created instance.</li>
<li>Message exchange: horizontal arrow.</li>
<li>Control flow: horizontal arrow with the 'call' prefix, dashed arrow for reply symbol, method and suspension symbols in between. </li>
<li>Timers: start, cancel, time out.</li>
<li>Time interval: relative and absolute with a dashed vertical arrow. </li>
<li>Conditions: usually used to represent a state of the underlying state machine.</li>
<li>Action: a box.</li>
<li>In-line expressions: alternative composition, sequential composition, exception, optional region, parallel composition, iteration (loop).</li>
<li>Reference: reference to another MSC. </li>
<li>Data concept: The user can use any data concept, if binding is undefined the default data concept is the one from <a href="/facts/Specification_and_Description_Language/dW7Q5zIe">SDL</a> as defined in Z.121 recommendation.</li>
<li>Coregion: a double dashed instance line to describe unordered events.</li></ul>
<h2 id="symbol-extensions">Symbol extensions</h2>
<ul><li><a href="/facts/SDL-RT/dW7Q5zIe">SDL-RT</a> has introduced:
<ul><li>a semaphore instance representation. </li>
<li>a save symbol to save messages.</li></ul></li></ul>
<h2 id="comparison-to-uml">Comparison to UML</h2>
<p>UML 2.0 <a href="/facts/Sequence_diagram/1goY7KId">Sequence Diagram</a> is strongly inspired by the ITU-T MSC. Still, for historical reasons, the default basic principles are quite different:
</p>
<ul><li>Lifelines</li></ul>
<ul><li>In an MSC, the vertical lines are autonomous execution entities. They usually represent state machines executing in parallel. The state machines need not be on the same computer.</li>
<li>In a Sequence Diagram, a vertical line is usually an object. The object can be active (in its own thread of execution) or passive (in the execution context of an active object).</li></ul>
<ul><li>Arrows</li></ul>
<ul><li>In an MSC an arrow is usually an asynchronous message sent from one entity to another one. Once the message is sent the sending entity resumes its execution.</li>
<li>In a Sequence Diagram an arrow is usually understood as an operation call on a class. It is therefore synchronous and the calling entity hangs until the operation returns.</li></ul>
<p>It has been said that MSC has been considered as a candidate for the <a href="/facts/Unified_Modeling_Language/3tlNS0tH">interaction diagrams</a> in UML.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p><p>However, proponents of MSC such as <a href="/facts/Ericsson/yJ4oMMp7">Ericsson</a> think that MSC is better than <a href="/facts/Unified_Modeling_Language/3tlNS0tH">UML 2.0</a> for modelling large or complex systems.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>
<h2 id="live-sequence-charts">Live Sequence Charts</h2>
<p><a href="/facts/David_Harel/scx315k0">David Harel</a> suggested that MSC had shortcomings such as:
</p>
<ul><li>MSC propose a weak <a href="/facts/Partially_ordered_set/qb4a3FAX">partial ordering</a> semantics that makes it impossible to capture some behavioral requirements,</li>
<li>The relationship between the MSC requirements and the executable specification is not clear,</li></ul>
<p>and proposed Live Sequence Charts (LSC) as an extension on the MSC standard .<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="http://www.di.univaq.it/psc2ba/">PSC</a> Property Sequence Chart, a way to describe properties in an MSC<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> or a Sequence Diagram.</li>
<li><a href="/facts/Specification_and_Description_Language/dW7Q5zIe">SDL</a> Specification and Description Language, an MSC related ITU-T language.</li>
<li><a href="/facts/Unified_Modeling_Language/3tlNS0tH">Interaction diagrams in UML</a>.</li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="http://www.itu.int/rec/T-REC-Z.120">ITU-T Recommendation Z.120</a> message sequence chart (MSC)</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"HMSC". sdl-forum.org. Retrieved 2009-09-19. <a href="http://www.sdl-forum.org/MSC2000present/sld005.htm" target="_blank">http://www.sdl-forum.org/MSC2000present/sld005.htm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Øystein Haugen. "MSC 2000" (PDF). Ericsson. Archived from the original (PDF) on 2011-06-07. Retrieved 2009-09-19. <a href="https://web.archive.org/web/20110607104113/http://folk.uio.no/intime/msc2000.pdf" target="_blank">https://web.archive.org/web/20110607104113/http://folk.uio.no/intime/msc2000.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>"What is new in MSC 2000 relative to MSC 96". sdl-forum.org. Retrieved 2009-09-19. <a href="http://www.sdl-forum.org/MSC2000present/sld007.htm" target="_blank">http://www.sdl-forum.org/MSC2000present/sld007.htm</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Ekkart Rudolph; Jens Grabowski; Peter Graubmann (1999). "Towards a Harmonization of UML-Sequence Diagrams and MSC". University of Göttingen. Retrieved 2014-08-25. <a href="http://www.swe.informatik.uni-goettingen.de/publications/towards-harmonization-uml-sequence-diagrams-and-msc" target="_blank">http://www.swe.informatik.uni-goettingen.de/publications/towards-harmonization-uml-sequence-diagrams-and-msc</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Øystein Haugen (June 2000). "UML 2.0 vs. SDL/MSC – Ericsson Position Statement" (PDF). Ericsson. Retrieved 2009-09-19. <a href="http://www.irisa.fr/manifestations/2000/sam2000/SLIDES/Haugen.pdf" target="_blank">http://www.irisa.fr/manifestations/2000/sam2000/SLIDES/Haugen.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>David Harel (2003-04-08). "Message Sequence Charts" (PDF). Archived from the original (PDF) on 2006-08-26. Retrieved 2009-09-20. <a href="/wiki/David_Harel" target="_blank">/wiki/David_Harel</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>David Harel (2005-02-22). "LSCs: Breathing Life into Message Sequence Charts". Formal Methods in System Design. 19: 45–80. doi:10.1023/A:1011227529550. S2CID 1551133. <a href="/wiki/David_Harel" target="_blank">/wiki/David_Harel</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>David Harel (2002). "Multiple instances and symbolic variables in executable sequence charts". ACM SIGPLAN Notices. 37 (11): 83–100. CiteSeerX 10.1.1.20.5984. doi:10.1145/583854.582429. <a href="/wiki/David_Harel" target="_blank">/wiki/David_Harel</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Emmanuel Gaudin; Eric Brunel (2013). SDL 2013: Model-Driven Dependability Engineering. Lecture Notes in Computer Science. Vol. 7916. Springer. pp. 19–35. doi:10.1007/978-3-642-38911-5_2. ISBN 978-3-642-38910-8. <a href="978-3-642-38910-8" target="_blank">978-3-642-38910-8</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
</ol>

Message sequence chart open-in-new

Message sequence chart