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The Timeline formalism. A visual formalism for expressing temporal constraints Eric Bodden. History . Developed by Smith, Holzmann , Etessami (Bell Labs) in 2001 Goal: to ease the specification of temporal patterns Have the visual spec translated into a low level spec which can be verified.

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the timeline formalism

The Timeline formalism

A visual formalism for expressing temporal constraints

Eric Bodden

history
History
  • Developed by Smith, Holzmann, Etessami (Bell Labs) in 2001
  • Goal: to ease the specification of temporal patterns
  • Have the visual spec translated into a low level spec which can be verified.

=> Model transformation!

problems with current ltl
Problems with current LTL
  • Example:When the phone goes offhook, a dialtone should occur.
  • In LTL:

!( !offhook U(offhook /\ X[](!dialtone /\ !onhook)) )

  • Already hard to read. But it comes worth…
requirements change
Requirements change!
  • Assume, an event i should be added in between offhook and response
  • Requires another nesting of Until formulae:

X((eventi /\ !onhook) U (eventi /\ !onhook))

  • Huge formulae, hard to understand.
solution
Solution
  • Circumvent awkward LTL syntax and use timeline notation instead
events
Events
  • A timeline consists of a sequence of the events of the following types
    • Regular events – e – may occur
    • Required events – r – must occur
    • Fail events – X – must not occur
semantics
Semantics
  • Fail events or required events must (not) happen depending on the context, i.e. on the events that have been seen before.
constraints
Constraints
  • Express that certain intermediate events can weaken the requirement.
  • Drawn as horizontal bars.
  • Can include or exclude start/end.
compositionality
Compositionality

Notion of sub-requirements

operational semantics
Operational semantics
  • Given by translation into Büchi automata (special FSM)
  • The automata reports an error if and only if it remains in an accepting state indefinitely.
statistics
Statistics
  • Specified 177 requirements
  • Average: 4 to 5 events and 2 to 3 constraints
  • Most complex one: 11 events and 7 constraints
  • 38% required events, remainder of events provides context
availability
Availability
  • Timeedit tool for Windows and Unix
  • Visual tool, generates Büchi automata and SPIN never claims

http://www.bell-labs.com/topic/swdist/

reading
Reading

Margaret H. Smith, Gerard J. Holzmann, Kousha Etessami

Events and Constraints: A Graphical Editor for Capturing Logic Requirements of Programs

Proceedings of the 5th IEEE International Symposium on Requirements Engineering table of contents

Pages: 14 - 22

Year of Publication: 2001

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