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Formale Methoden der Systemspezifikation Logische Spezifikation von Hard- und Software

Formale Methoden der Systemspezifikation Logische Spezifikation von Hard- und Software. Prof. Dr. Holger Schlingloff Institut für Informatik der Humboldt Universität und Fraunhofer Institut für Rechnerarchitektur und Softwaretechnik. Aufbau der Veranstaltung.

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Formale Methoden der Systemspezifikation Logische Spezifikation von Hard- und Software

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  1. Formale Methoden der SystemspezifikationLogische Spezifikation von Hard- und Software Prof. Dr. Holger Schlingloff Institut für Informatik der Humboldt Universität und Fraunhofer Institut für Rechnerarchitektur und Softwaretechnik

  2. Aufbau der Veranstaltung • Blockkurs „Algebraische Spezifikation von Software und Hardware“ • Dr. Markus Roggenbach, Univ. Swansea • voraussichtlich 23.-25.5. und 30.5.-1.6.2008 (n.V.) • wie im SS2007 (VL & Ü) • Vorlesung (2SWS) „Logische Spezifikation“ • diese Veranstaltung • Übungsaufgaben zur VL • Dipl. Inf. Jan Calta, CZ • Bearbeitung zum Bestehen der Prüfung essentiell

  3. Lernziele • Kenntnisse über formale Spezifikationsmethoden zur Festlegung der Funktion von Systemen • Historische Entwicklung, Stärken/Schwächen, Möglichkeiten und Grenzen • Fähigkeiten, diese für praktische Anwendungen einsetzen zu können • Spielbeispiele / realistische Systeme • industrielles Interesse (vgl. IEC61508) • Umgang mit formalen Werkzeugen • Checker, Prover, Transformatoren, …

  4. Einordnung • praktische Informatik • Spezifikation ist Teil der Systementwicklung • Bezug zur theoretischer Informatik • Verwandtes Modul: „Methoden und Modelle des Systementwurfs“ (W. Reisig) • Fokus: hier Spezifikation, dort Modellierung • fließende Übergänge, aber kaum Überlappung • Methodenwissen ähnlich • Weitere Bezüge • Modellbasierte Softwareentwicklung (J. Fischer) • Logik, Spiele und Automaten (M. Grohe) • …

  5. weitere Ankündigungen • Einschreibung in GOYA? • Studien- und Diplomarbeiten • Jobs bei FIRST • Sokrates-Austausch mit UWales@Swansea • Folien in Englisch?

  6. Definition of Terms • System = „something composed“, i.e., everything • here only: computational system (SW/HW) • computation = transformation or transport of information • Specification = written description of a system • „species facere“, making something visible • can be informal or formal (we consider formal specs only) • Formal = in a certain fixed appearance • syntax, semantics, derivation • Logic = principles of reasoning • logos = word, thought, reason • „logic“ can also denote a certain formal language

  7. Specification of Systems • Should be one of the first activities in software development • requirements  specification  modelling  module decomposition  implementation  integration  deployment • Often neglected, mostly only informal • Quality problems, acceptance problems • Specification „a posteriori“

  8. Motivation FIRST: “Understanding and mastering complex systems” Examples: • a video camera • a car control unit • a banking machine system • a mobile phone communication protocol • a fault tolerant computer for routing of trains • an aircraft mission management system • Understanding:Being able to describe what these systems are supposed to do • Mastering: Being able to check whether they do what they are supposed to do  Understanding and mastering human behaviour?

  9. A first example A new video camcorder (“DCR-PC330”) • owner's manual almost incomprehensible • can be found in the internet • typical for such devices • Multifunctional on-off switch: • up: off • down: cycles through "tape", "memory" and "play/edit" mode • Intuitively, tape mode is for video, memory mode for pictures and play mode for viewing recorded material

  10. off tape play dn up up up dn dn memory dn Transition system • How can we formally describe the behaviour of this switch? (Natural language description is ambivalent: What does "cycle" mean? What if I push dn-dn-up-dn?) • Modelling by finite transition system: • States: {off, tape, memory, play} • Transition relations: {up, dn}

  11. Hybrid logic • An alternative way to describe this switch: modal theory (description logic T-Box) (For experts: additional axioms necessary, such as nondeterminism p -> []p) (For nonexperts: I assume you know about propositional logic) tape dn memory up off memory dn play up off play dn tape up off off dn tape  [up] false

  12. Modal logic Classical modal logic does not allow the use of state names. • Boolean properties describing the states: (For experts: additional axioms necessary to inhibit impossible states) (For the experts: this is a boolean encoding with three propositions.In principle, two would be enough, since on  rec  dv ) {tape, memory, play}||- on off||-  on /* on = powered */ {tape, memory}||- rec {play, off}||- rec /* rec = can record */ {tape, play}||- dv {memory, off}||- dv /* dv = head spinning */ • off ||-  on  rec  dv • tape ||- on  rec  dv • memory ||- on  rec  dv • play ||- on  rec  dv

  13. Signature: P={on, rec, dv}, R={up, dn} Language: Some valid properties: • rec  dv  on • on  [up] on • on dn on • dv dn (dv dndv)

  14. Unique description of the behaviour of this switch!? • Questions I might ask: • in which state is the camcorder if I push dn-dn-up-dn? dndnupdn tape or dndnupdn (dv  rec) • can I always switch it off? upon • how long will it stay on if I don't? • In practice, no spec is ever complete! power failure while on shuts system off, power resume brings it to “tape" mode

  15. offbut_hi dn up up up tape play dn dn dn memory pwr_fail offbut_lo pwr_resume • to model power failures, we have to distinguish between the state of the button (but_hi, but_lo) and the state of the camcorder (off, tape,...)

  16. play tape camera switch on but_hi but_lo off dn memory dn,pwr_res dn up up,pwr_fail dn dn on dn • Every model abstracts from details (e.g., there is a little green button within the switch which arrests it in the "off" position) • A model is a means of communication between humans (designers, users, ...) • Structuring the model as parallel hierarchical transition system gives a statechart / state machine diagram

  17. Such models can help in the development of complex systems ("model-driven design") • The more concrete the formalism, the closer it is to an implementation • executable code may be generated from state diagrams • We might add additional information such as timing, communication, variables and such. • Specification as opposed to modeling describes properties of the targeted system • not aiming at a complete description of the system • not aiming at the generation of executable code

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