The Timeline formalism

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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

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

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

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
• Circumvent awkward LTL syntax and use timeline notation instead
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
• Fail events or required events must (not) happen depending on the context, i.e. on the events that have been seen before.
Constraints
• Express that certain intermediate events can weaken the requirement.
• Drawn as horizontal bars.
• Can include or exclude start/end.
Compositionality

Notion of sub-requirements

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
• 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
• Timeedit tool for Windows and Unix
• Visual tool, generates Büchi automata and SPIN never claims

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