The Timeline formalism

1
The Timeline formalism

• A visual formalism for expressing temporal
  constraints
• Eric Bodden

2
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.
• gt Model transformation!

3
Problems with current LTL

• ExampleWhen the phone goes offhook, a dialtone
  should occur.
• In LTL
• !( !offhook U(offhook /\ X(!dialtone /\
  !onhook)) )
• Already hard to read. But it comes worth

4
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.

5
Solution

• Circumvent awkward LTL syntax and use timeline
  notation instead

6
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

7
Semantics

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

8
Constraints

• Express that certain intermediate events can
  weaken the requirement.
• Drawn as horizontal bars.
• Can include or exclude start/end.

9
Scalability adding an event
10
Compositionality

• Notion of sub-requirements

11
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.

12
Example with constraints
13
Fail events
14
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

15
Availability

• Timeedit tool for Windows and Unix
• Visual tool, generates Büchi automata and SPIN
  never claims
• http//www.bell-labs.com/topic/swdist/

16
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