page_title: Message sequence chart
section_title: Symbols in MSC
hierarchical_section_title: Message sequence chart / Symbols in MSC
caption_attribution_description: English: Time constraint in an MSC
context_page_description: A message sequence chart is an interaction diagram from the SDL family standardized by the International Telecommunication Union.
  The purpose of recommending MSC is to provide a trace language for the specification and description of the communication behaviour of system components and their environment by means of message interchange. Since in MSCs the communication behaviour is presented in a very intuitive and transparent manner, particularly in the graphical representation, the MSC language is easy to
  learn, use and interpret. In connection with other languages it can be used to support methodologies for system specification, design, simulation, testing, and documentation.
context_section_description: The existing symbols are:
  MSC head, lifeline, and end: a vertical line with a box at the top, and a box or a cross at the bottom.
  Instance creation: horizontal dashed arrow to the newly created instance.
  Message exchange: horizontal arrow.
  Control flow: horizontal arrow with the 'call' prefix, dashed arrow for reply symbol, method and suspension symbols in between. 
  Timers: start, cancel, time out.
  Time interval: relative and absolute with a dashed vertical arrow. 
  Conditions: usually used to represent a state of the underlying state machine.
  Action: a box.
  In-line expressions: alternative composition, sequential composition, exception, optional region, parallel composition, iteration (loop).
  Reference: reference to another MSC. 
  Data concept: The user can use any data concept, if binding is undefined the default data concept is the one from SDL as defined in Z.121 recommendation.
  Coregion: a double dashed instance line to describe unordered events.
caption: Time constraint in an MSC
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