LTLf and LDLf Monitoring: A Technical Report

Runtime monitoring is one of the central tasks to provide operational decision support to running business processes, and check on-the-fly whether they comply with constraints and rules. We study runtime monitoring of properties expressed in LTL on finite traces (LTLf) and in its extension LDLf. LDLf is a powerful logic that captures all monadic second order logic on finite traces, which is obtained by combining regular expressions and LTLf, adopting the syntax of propositional dynamic logic (PDL). Interestingly, in spite of its greater expressivity, LDLf has exactly the same computational complexity of LTLf. We show that LDLf is able to capture, in the logic itself, not only the constraints to be monitored, but also the de-facto standard RV-LTL monitors. This makes it possible to declaratively capture monitoring metaconstraints, and check them by relying on usual logical services instead of ad-hoc algorithms. This, in turn, enables to flexibly monitor constraints depending on the monitoring state of other constraints, e.g., "compensation" constraints that are only checked when others are detected to be violated. In addition, we devise a direct translation of LDLf formulas into nondeterministic automata, avoiding to detour to Buechi automata or alternating automata, and we use it to implement a monitoring plug-in for the PROM suite

VERIFICATION OF CONJUNCTIVE ARTIFACT-CENTRIC SERVICES

An artifact-centric service is a stateful service that holistically represents both the data and the process in terms of a (dynamic) artifact. An artifact is constituted by a data component, holding all the data of interest for the service, and a lifecycle, which specifies the process that the service enacts. In this paper, we study artifact-centric services whose data component is a full-fledged relational database, queried through (first-order) conjunctive queries, and the lifecycle component is specified as sets of condition-action rules, where actions are tasks invocations, again based on conjunctive queries. Notably, the database can evolve in an unbounded way due to new values (unknown at verification time) inserted by tasks. The main result of the paper is that verification in this setting is decidable under a reasonable restriction on the form of tasks, called weak acyclicity, which we borrow from the recent literature on data exchange. In particular, we develop a sound, complete and terminating verification procedure for sophisticated temporal properties expressed in a first-order variant of µ-calculus

Runtime Enforcement of First-Order LTL Properties on Data-Aware Business ProcessesService-Oriented Computing

none2Riccardo De Masellis;Jianwen SuDe Masellis, Riccardo; Jianwen, S

Reasoning on LTL on Finite Traces: Insensitivity to Infiniteness

In this paper we study when an LTL formula on finite traces (LTLf formula) is insensitive to infiniteness, that is, it can be correctly handled as a formula on infinite traces under the assumption that at a certain point the infinite trace starts repeating an end event forever, trivializing all other propositions to false. This intuition has been put forward and (wrongly) assumed to hold in general in the literature. We define a necessary and sufficient condition to characterize whether an LTLf formula is insensitive to infiniteness, which can be automatically checked by any LTL reasoner. Then, we show that typical LTLf specification patterns used in process and service modeling in CS, as well as trajectory constraints in Planning and transition-based LTLf specifications of action domains in KR, are indeed very often insensitive to infiniteness. This may help to explain why the assumption of interpreting LTL on finite and on infinite traces has been (wrongly) blurred. Possibly because of this blurring, virtually all literature detours to Büchi automata for constructing the NFA that accepts the traces satisfying an LTLf formula. As a further contribution, we give a simple direct algorithm for computing such NFA.

Composition of partially observable services exporting their behaviour

In this paper we look at the problem of composing services that export their behavior in terms of a transition system, characterizing the choices of actions given to a client at each point in time. The composition consists of synthesizing an orchestrator that coordinates the available services so as to mimic the desired target service asked by the client. Specifically, in this paper we study the "conformant form" of the problem, where available services are partially controllable and partially observable, and hence, the orchestrator has to make its decisions exploiting the observations made so far only. We give a sound and complete procedure to synthesize the orchestrator in such case, and characterize the computational complexity of the problem. The procedure is based on working with belief (or knowledge) states, a standard technique to tackle conformant planning. Moreover we show that, although in general unavoidable, the powerset construction at the base of the belief state approach can be delegated to the symbolic manipulations of the game-structure model checking tool (TLV), which can be used to efficiently implement the orchestrator synthesis procedure. Copyright © 2009, Association for the Advancement of Artificial Intelligence. All rights reserved