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# The Timeline formalism - PowerPoint PPT Presentation

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

A visual formalism for expressing temporal constraints

Eric Bodden

• 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!

• Example:When the phone goes offhook, a dialtone should occur.

• In LTL:

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

• 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.

• Circumvent awkward LTL syntax and use timeline notation instead

• 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

• Fail events or required events must (not) happen depending on the context, i.e. on the events that have been seen before.

• Express that certain intermediate events can weaken the requirement.

• Drawn as horizontal bars.

• Can include or exclude start/end.

Notion of sub-requirements

• Given by translation into Büchi automata (special FSM)

• The automata reports an error if and only if it remains in an accepting state indefinitely.

• 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

• Timeedit tool for Windows and Unix

• Visual tool, generates Büchi automata and SPIN never claims

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

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

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