Lecture Notes ni Computer Science Edited yb .G Goos and .J Hartmanis 354 II I J.W. de Bakker W.-R de Roever G. Rozenberg ).sdE( Linear Time, Branching Time and Partial Order ni Logics dna Models rof Concurrency School/Workshop, Noordwijkerhout, ehT sdnalrehteN yaM 30- June ,3 8891 I II I Springer-Verlag nilreB Heidelberg London NewYork Paris oykoT Editorial Board D. Barstow W. Brauer .P Brinch Hansen D. Gries D. Luckham C. Moler A. Pnueli G. Seegm~ller .J Stoer N. Wirth Editors .1. .W de Bakker Centre for Mathematics and Computer Science Kruislaan 413, 1098 SJ Amsterdam, The Netherlands W.-P. de Roever Departmento f Computing Science Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven, The Netherlands G. Rozenberg Institute of Applied Mathematics and Computer Science University of Leiden P.O. Box 9512, 2300 RA Leiden, The Netherlands CR Subject Classification (1987): B.1, C.1-2, D.4, El, F.3-4 ISBN 3-540-51080-X Springer-Verlag Berlin HeidelbergN ew York ISBN 0-387-51080-X Springer-Verlag New York Berlin Heidelberg sihT work si tcejbus ot .thgirypoc llA sthgir era ,devreser rehtehw eht of part or whole eht lairetam si ,denrecnoc yllacificeps eht sthgir fo ,noitalsnart ,gnitnirper esu-er fo ,snoitartsulli ,noitaticer ,gnitsacdaorb noitcudorper no smliforcim or ni other ,syaw dna egarots ni data .sknab noitacilpuD this of noitacilbup or strap foereht si only dettimrep rednu eht snoisivorp fo eht namreG thgirypoC waL of rebmetpeS ,9 ,5691 sti ni noisrev of enuJ ,42 ,5891 dna a thgirypoc eef tsum syawta eb .diap snoitaloiV fall rednu the noitucesorp tca of eht namreG thgirypoC .waL © galreV-regnirpS Berlin grebledieH t 989 detnirP ynamreG ni gnitnirP dna :gnidnib suahkcurD ,ztleB .rtsgreB/hcabsmeH 214513140-543210 - detnirP no eerf-dica repap ECAFERP Modelling the behaviour of concurrent dna distributed systems sah nworg into eno of the most challenging dna vigorous research areas within theoretical computer science. ehT last edaced sah seen the ecnegreme of three independent sehcaorppa to this problem, emos of them capturing differences neewteb systems that others ignore. ehT first eno sledom a system yb describing its execution runs, the dnoces eno yb analysing the execution trees, dna the third eno sledom a system yb describing the (in)dependencies dna choices neewteb the various events that yam occur. Paradigmatic for these sehcaorppa era semantic sniamod with linear or branching elements, linear time dna branching time temporal logic, dna net theory. Although it smees that the erom features a captures system the better, if eno wants emos erusaem of abstractness dna parsimony, emos of such features yam eb too detailed for a given level of description. This reviews volume these intrinsically different sehcaorppa dna evaluates their relative .segatnavda It is desab no the pohskroW/loohcS" nO Linear Time, Branching Time dna Partial Order in Logics dna Models for Concurrency" organized yb the editors dna held in the period yaM 03 - June 3, 8891 at Noordwijkerhout, ehT Netherlands. ehT pohskroW/loohcS saw na activity of the project XER - hcraeseR dna Education in Concurrent smetsyS sponsored yb the Netherlands IFN (Nationale Faciliteit Informatica) .emmargorP ehT meeting saw organized under auspices of the SCTAE dna saw furthermore supported yb the Centre for Mathematics dna retupmoC Science, the University of Leiden, dna the nevohdniE University of Technology. ehT material presented in this volume sah been prepared yb the lecturers (and their coauthors) after the meeting took place - in this yaw the srepap reflect also the vivid discussions that took place during the meeting. eW era proud that ew dah such na excellent group of lecturers dna such na eager dna enthusiastic group of participants. eW era very grateful to both groups for gnikam the meeting both scientifically interesting dna socially very pleasant, dna to the margorP eettimmoC consisting of .M ,yssenneH E.-R. Olderog, .A Pnueli, J. Sifakis, dna P.S. Thiagarajan for their help in preparing the scientific margorp of the meeting. eW gratefully egdelwonkca the financial support from the Netherlands National Facility for Informatics (NFI). ehT Centre for Mathematics dna retupmoC Science saw responsible for the ~echnical organization of the meeting. ehT University of Leiden dna the nevohdniE University of cooperated have Technology in the organization no a rebmun of vital points. sA directors of the pohskroW/loohcS ew want to extend our special thanks to .sM Loes ,rekamesraaK-lemsaV .sM Marja Hegt, dna .rM Frans Snijders for organizational assistance dnoyeb the call of duty. VI eW epoh that in the future tnempoleved of the theory of concurrent smetsys this emulov yam help in bringing at least partial order into the gnihcnarb structure that this tnempoleved undoubtedly will .evah January, 9891 ehT Editors, .W.J ed rekkaB .P.W ed reveoR .G grebnezoR EHT XER TCEJORP ehT XER - hcraeseR dna Education in Concurrent Systems-project investigates syntactic, semantic dna proof-theoretic aspects of concurrency. In addition, its objectives era the education of gnuoy researchers ,dna in general, the dissemination of scientific results relating to these .semeht XER is a collaborative effort of the Leiden University oG( ,)grebnezoR the Centre for scitamehtaM dna retupmoC Science in madretsmA (J.W. ed Bakker), dna the nevohdniE University of ygolonhceT .P.W( ed Roever), representing the areas syntax, semantics dna proof theory, respectively. ehT project is detroppus yb the Netherlands National Facility for Informatics (NFI); its detcepxe duration is four years starting 'in 1988. In the years ,8891-4891 the emas groups together dekrow in the Netherlands National ycnerrucnoC Project ,)CPL( supported yb the Netherlands noitadnuoF for the tnemecnavdA of eruP hcraeseR .)OWZ( ehT research activities of the XER project will include, erom specifically, (i) Three subprojects devoted to the :semeht - syntax of concurrent :smetsys a graph oriented krowemarf for structures dna sessecorp - process theory dna the semantics of parallel logic gnimmargorp segaugnal high-level specification dna refinement of real-time distributed .smetsys (ii) Collaboration with visiting professors dna post-doctoral researchers, in particular focused no the research semeht denoitnem .evoba In 9891/8891 these visitors include dr. E.-R. Olderog (Kiel), prof. P.S. Thiagarajan (Madras), dr. .S hsemaR (Indian Institute of Technology). (iii) spohskroW dna Schools. ehT pohskroW/loohcS no Linear Time, gnihcnarB emiT dna Partial Ordeirn Logics dna sledoM for ycnerrucnoC saw the first in a series of hcus events. roF ,9891 ew plan a pohskrow no "Stepwise tnemenifeR of Distributed :smetsyS Models, ,smsilamroF Correctness". In ,0991 ew shall organize a meeting no "Actor ,smetsys object-oriented segaugnal dna massive parallelism" (tentative title). ehT educational activities of XER include regular "concurrency days". A ycnerrucnoc yad yam consist of tutorial introductions to selected topics, dna of presentations of research results to a non-specialist audience. Often, experts from daorba era invited to contribute to these days. In addition, visiting professors era deksa to present lecture series concerning recent stnempoleved in their fields of specialization. Clearly, the spohskroW/loohcS lV evah sa well na important educational function, providing their participants with na intensive introduction to wen areas. Finally, ew mention another aspect of the XER project. eW shall continue the regular contacts with other naeporuE projects in eht area of Ycnerrucnoc built pu during the CPL years. In particular, this applies to the hcnerF 3 -Cooperation, C ,noitacinummoC -ycnerrucnoC program, to the British retupmoC Society - lamroF Aspects of retupmoC Science group, dna to groups within the Gesellschaft fQr kitamehtaM dnu Datenverarbeitung )DMG( in .nnoB sA denoitnem already, XER continues the CPL cooperation. emoS highlights of the CPL years are: (i) the organization of the CPL/TIRPSE decnavdA loohcS no Current sdnerT in ycnerrucnoC (1985, proceedings deraeppa sa Lecture Notes in retupmoC Science, Vol. 224, Springer, ;)6891 (ii) Ph.D. research no the topics vector synchronized ,smetsys dataflow ,scitnames dna real-time temporal logic; (iii) fruitful interaction with TIRPSE projects 514 (Parallel Architectures dna segaugnaL for AIP: a VLSI-directed )hcaorppa dna 739 (Descartes, gniggubeD dna Specification of ADA Real-Time deddebmE Systems). CPL contributed to the local organization of TIRPSE 514 conference ELRAP - Parallel Architectures dna segaugnaL eporuE (1987, sgnideecorP deraeppa sa Lecture Notes in retupmoC Vol. Science 258, 259, Springer); (iv) eht setting-up of the international segnahcxe referred to .evoba eW would like to conclude this brief presentation of the future (past) of the XER )CPL( project yb inviting everyone ohw is interested in erom information concerning XER (possibility of visits, plans for ,spohskrow other forms of ,segnahcxe etc.) to write to eno of the project leaders. .W.J ed rekkaB .P.W ed reveoR .G grebnezoR STNETNOC ECAFERP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V EHT XER TCEJORP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VII SLAIROTUT J. van Benthem Time, logic and computation . . . . . . . . . . . . . . . . . . . . . . . . 1 J.A. Bergstra, J.W. Klop Process theory based no bisimulation semantics . . . . . . . . . . . . . . . 05 E.A. ,nosremE J. Srinivasan Branching time temporal logic . . . . . . . . . . . . . . . . . . . . . . . 321 .M yssenneH 371 Observing processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Z ,annaM .A Pnueli 102 ehT anchored version of the temporal framework . . . . . . . . . . . . . . . .A Mazurkiewicz 582 Basic notions of trace theory . . . . . . . . . . . . . . . . . . . . . . . .G Winskel 463 nA introduction to event structures . . . . . . . . . . . . . . . . . . . . LACINHCET SNOITUBIRTNOC .A Bouajjani, .S Graf, J. Sifakis A logic for the description of behaviours dna properties of concurrent systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 893 .G Boudol, I. Castellani Permutation of transitions: nA event structure semantics for SCC dna SCCS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 .M.E Clarke, I.A. Draghicescu Expressibility results for linear-time dna branching-time logics ...... 824 VIII .P ,onageD .R eD Nicola, .U Montanari Partial orderings descriptions dna observations of nondeterministic 834 concurrent processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . .H namfiaG Modeling concurrency yb partial orders dna nonlinear transition systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764 .S Katz, .D Peled nA efficient verification dohtem for parallel dna distributed 984 smargorp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .K Lodaya, .R ,majunamaR P.S. Thiagarajan A logic for distributed transition systems . . . . . . . . . . . . . . . . . 805 .M Nielsen, .U Engberg, K.S. Larsen Fully abstract models for a process language with refinement . . . . . . . . 325 E.-R. Olderog Strong bisimilarity no nets: a wen concept for comparing net semantics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 945 .A Rabinovich, B.A. Trakhtenbrot Nets of processes dna data flow . . . . . . . . . . . . . . . . . . . . . . 475 .W Reisig sdrawoT a temporal logic of causality dna choice in distributed systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 .M.MoJ.J Rutten Correctness dna full abstraction of metric semantics for concurrency .... 826 .C Stirling laropmeT logics for SCC . . . . . . . . . . . . . . . . . . . . . . . . . . 066 .W.M Shields Behavioural Presentations . . . . . . . . . . . . . . . . . . . . . . . . . 376 .W samohT noitatupmoC tree logic dna regular w-languages . . . . . . . . . . . . . . . 096 TIME, LOGIC AND COMPUTATION Johan van Benthem Faculty of Mathematics and Computer Science University of Amsterdam Roetersstraat 15, 1018 WB Amsterdam, Holland ABSTRACT. This paper startsw ith a survey of temporal logic in its original guise, pointing at its connections with philosophy and linguistics. More specifically, a technical exposition is provided of the basic 'tense-logical' system, baseodn points or 'moments' of time, with the research program in model theory and proof theory which has grown around it. After that, a more recent stream of 'period' and 'event' based approaches to time is discussed, again with some of the new logical themes engendered by it. Finally, a review isg iven of some recent computational research in temporal logic. Here, a clear continuity of logical concerns emerges between philosophy, linguistics and computer science. But, the latter adds severnaelw themes and perspectives which might well give it a significant impact on the earlier standard enterprise. Keywords. Completeness, computational semantics, correspondence, event structure, first-order definability, period structure, point structure, temporal operator, tense logic. CONTENTS 1 Introduction 2 Points 2.1 Basic Framework 2.2 Axiomatics 2.3 Model Theory 2.4 Further Developments 3 Periods and Events 3,1 Basic Period Ontology 3.2 Temporal Logic 3.3 Relating Points and Periods 3.4 Extending to Events 4 Perspectives from Computer Science 4.1 Application with Innovation 4.2 Semantic Parallels 4.3 Reinterpreting Logic 1. Introduction The formal properties of Time have attracted the attention of philosophers and mathematicians ever since Antiquity (cf. the anthology Smart 1964). Moreover, abstract temporal structure finds its reflection in our linguistic habits of temporal reasoning, and hence logicians have entered this field too, creating a discipline of 'temporal logic' (Reichenbach 1947, Prior 1957, Prior 1967). But in fact, time is a phenomenon cutting across many academic boundaries: from physics (cf. Reichenbach 1957) to psychology (cf. Michon & Jackson 1985). [A reference spanning virtually this whole spectrum is Whitrow 1980.] Within this wider area, temporal logic finds itself in particularly close contact with philosophy, linguistics (cf. Dowty 1979) and increasingly also with computer science. For, these disciplines share an interest in creating exact systems of temporal representation, coming with calculfio r reasoning about change or persistence over time. The purpose of this paper is twofold. On the one hand, a discursive survey will be given of temporal logic as it has developed in this century - while on the other, there is a review of recent contacts with computer science; whose variety, after a mere decade of research, is already impressive. No complete coverage has been attempted, however, in either respect. For furtherd etails on temporal logic, there is an array of informative texts, such as Gabbay 1976, van Benthem 1983, Burgess 1984 and Goldblatt 1987a. Moreover, the present volume itself may be viewed as an anthology of computational research into temporal logic. Therefore, we shall feel free to choose our own path through the area, with an emphasis on general research lines, and an occasional new question or observation. 2. Points 2.1 Basic Framework 2.1.1 An instructive, and much-studied 'minimal' system of temporal logic was developed by Arthur Prior in the fifties and sixties. This so-called 'tense logic' has propositional operators P forpast and F for future. The original motivation for concentrating on these was two-sided. Philosophically, these are the basic operators which assign changing temporal 'perspective' to events. I.e., they express the dynamic 'A- series' of McTaggart 1908, who contrasted this with the static 'B-series' of an immutable order of events. In Prior's system, B-series models provide the semantics for A-series languages, as we shall see, But also, linguistically, the operators P, F correspond to the most basic 'tenses' of natural language: q : Mary cries (present) Pq : Mary cried (past) Fq : Mary will cry (future). Further iterations then reflect compound tenses: PPq : Mary had cried (pastp erfect) FPq : Mary will have cried (future perfect), etcetera. The analogy is by nom eans without its problems: but it has had undeniable heuristic virtues.