CTL and ACTL patterns
This document presents an overview of CTL (Computation Tree Logic) and ACTL (Action Computation Tree Logic) patterns, essential for specifying properties in system models. It introduces temporal logics, detailing their operators and quantifiers, and emphasizes the importance of patterns in formulating valid logic expressions. Examples illustrate the use of CTL and ACTL in practice, highlighting potential pitfalls and providing guidance for engineers. The document concludes by discussing the construction of complex formulae and the integration of natural language specifications into temporal logic.
CTL and ACTL patterns
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Presentation Transcript
CTL and ACTL patterns Robert Meolic, Tatjana Kapus, Zmago Brezočnik Faculty of Electrical Engineering and Computer Science University of Maribor
CTL and ACTL patterns Description of system • Introduction • Temporal logics • CTL • ACTL • Why patterns? • Some examples • Conclusion Specification of properties AG [red!] A [{trainCross!} U {green!}] EF (EX {trainCross!} EX {carCross!})
Introduction • System = states + transitions • Kripke structure: state predicates • Labelled transition system (LTS): action predicates Kripke structure LTS p a a r r b a b a p p q p a b c q r
Temporal logics • Standard Boolean operators • Path quantifiers: A, E A E • Temporal operators: X, F, G, U X p This example is for CTLFor ACTL it is similar F p p p p p p G p p p q U
CTL – Computation tree logic EX p AX p A state where CTL formula p is valid is p-state p p p EF p AG p E[p U q] p p p p p p p p p q p p p
ACTL – Action CTL EX{a}p EF{a}p a A transition containing action predicate alphawhich is leading to the statewhere ACTL formula p is validis (alpha,p)-transition p a p • There are some abbreviations, e.g. Hennessy-Milner operators • < a > p = EX {a} p • [ a ] p = NOT EX {a} NOT p EG{a}p p a p a p a p
Why patterns? • Forming CTL and ACTL formulae is a complex task • Required are theoretical background and experience • There is a danger that the formula DOES NOT express the property which an engineer intended to express • Patterns of formulae are very useful help
Some examples • Always in the future, if q is valid, then p is valid all the time before it • Always in the future, if q is valid, then p is valid all the time after it • if q is valid in the future for the last time, then p is valid for at least one time before it
More examples • Classification of patterns presented by M. Dwyer • ABSENCE: p is false after q • PRECEDENCE: s precedes p between q and r
Conclusion • For model checking CTL and ACTL formulae are needed • Patterns enable the construction of complex formulae • The goal is automatic translation from NATURAL LANGUAGE to TEMPORAL LOGIC Our ACTL model checker EST is available at http://www.el.feri.uni-mb.si/est/ Comments and questions: meolic@uni-mb.si
