The timeline formalism
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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

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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.


Scalability adding an event

Scalability – adding an event


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.


Example with constraints

Example with constraints


Fail events

Fail events


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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