Commit e5124faa authored by Alexandre Duret-Lutz's avatar Alexandre Duret-Lutz
Browse files

man: more doc about TGBA and monitors

This was prompted by an exchange of emails with Caroline Lemieux.

* src/bin/man/ltl2tgba.x: Add notes and references.
* NEWS, THANKS: Update.
parent d4e3a952
New in spot 1.2.4a (not yet released)
* Documentation
- The man page for ltl2tgba has some new notes and references
about TGBA and about monitors.
* Bug fixes:
- Fix simplification of bounded repetition in SERE formulas.
......@@ -2,6 +2,7 @@ We are grateful to these people for their comments, help, or
Akim Demaille
Caroline Lemieux
Christian Dax
Ernesto Posse
Étienne Renault
ltl2tgba \- translate LTL/PSL formulas into Büchi automata
TGBA stands for Transition-based Generalized Büchi Automaton. The
name was coined by Dimitra Giannakopoulou and Flavio Lerda in their
FORTE'02 paper (From States to Transitions: Improving Translation of
LTL Formulae to Büchi Automata), although similar automata have been
used under different names long before that.
As its name implies a TGBA uses a generalized Büchi acceptance
condition, meanings that a run of the automaton is accepted iff it
visits ininitely often multiple acceptance sets, and it also uses
transition-based acceptance, i.e., those acceptance sets are sets of
transitions. TGBA are often more consise than traditional Büchi
automata. For instance the LTL formula \f(CWGFa & GFb\fR can be
translated into a single-state TGBA while a traditional Büchi
automaton would need 3 states. Compare
% ltl2tgba 'GFa & GFb'
% ltl2tgba --ba 'GFa & GFb'
In the dot output produced by the above commands, the membership of
the transitions to the various acceptance sets is denoted using names
in braces. The actuall names do not really matter as they may be
produced by the translation algorithm or altered by any latter
When the \fB\--ba\fR option is used to request a Büchi automaton, Spot
builds a TGBA with a single acceptance set, and in which for any state
either all outgoing transitions are accepting (this is equivalent to
the state being accepting) or none of them are. Double circles are
used to highlight accepting states in the output, but the braces
denoting the accepting transitions are still shown because the
underling structure really is a TGBA.
The format, described at,
......@@ -10,7 +47,7 @@ internally, it will normally use the transition-based flavor of that
format, indicated with a 't' flag after the number of acceptance sets.
For instance:
% bin/ltl2tgba --lbtt 'GFp0 & GFp1 & FGp2'
% ltl2tgba --lbtt 'GFp0 & GFp1 & FGp2'
2 2t // 2 states, 2 transition-based acceptance sets
0 1 // state 0: initial
0 -1 t // trans. to state 0, no acc., label: true
......@@ -80,6 +117,38 @@ p[0-9]+ as double-quoted strings.
0 -1 & ! "b" ! "a"
The monitors generated with option \fB\-M\fR are finite state automata
used to reject finite words that cannot be extended to infinite words
compatible with the supplied formula. The idea is that the monitor
should progress alongside the system, and can only make decisions
based on the finite prefix read so far.
Monitors can be seen as Büchi automata in which all recognized runs are
accepting. As such, the only infinite words they can reject are those
are not recognized, i.e., infinite words that start with a bad prefix.
Because of this limited expressiveness, a monitor for some given LTL
or PSL formula may accept a larger language than the one specified by
the formula. For instance a monitor for the LTL formula \f(CWa U b\fR
will reject (for instance) any word starting with \f(CW!a&!b\fR as
there is no way such a word can validate the formula, but it will not
reject a finite prefix repeating only \f(CWa&!b\fR as such a prefix
could be extented in a way that is comptible with \f(CWa U b\fR.
For more information about monitors, we refer the readers to the
following two papers (the first paper describes the construction of
the second paper in a more concise way):
Deian Tabakov and Moshe Y. Vardi: Optimized Temporal Monitors for SystemC.
Proceedings of RV'10. LNCS 6418.
Marcelo d’Amorim and Grigoire Roşu: Efficient monitoring of
ω-languages. Proceedings of CAV'05. LNCS 3576.
If you would like to give a reference to this tool in an article,
we suggest you cite one of the following papers:
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