Event Calculus Research Articles

Specifying features of an evolving software system

AbstractSoftware development is increasingly concerned with maintaining and extending existing software systems to meet the evolving user requirements. Many of these systems are feature‐rich and are developed incrementally. As structures of existing software systems—in addition to the user requirements—influence the specifications, specifying these systems poses unique challenges. This paper reports on our experience of applying an engineering approach to specifying an evolving feature‐rich television software system. In this approach, features are specified modularly by first fitting their problems to known problem patterns, and then analyzing typical concerns—meaning the potential causes of errors—associated with those patterns. In cases where the existing design poses difficulties when fitting problems to patterns, we transform its structure using known design mechanisms so that the problems fit the patterns. After deriving specifications of individual features, possible interactions between features are detected, before declaratively specifying resolutions to undesired interactions. As the concerns of features and their composition are addressed separately, the specifications derived are modular, thus, providing rich treaceability to their requirements. As well as discussing how features may be specified using natural language, we also show how their descriptions may be formalized using a form of temporal logic called the Event Calculus, and prove their correctness using an off‐the‐shelf tool. Copyright © 2009 John Wiley & Sons, Ltd.

Policy conflict analysis for diffserv quality of service management

Policy-based management provides the ability to (re-)configure differentiated services networks so that desired Quality of Service (QoS) goals are achieved. This requires implementing network provisioning decisions, performing admission control, and adapting bandwidth allocation to emerging traffic demands. A policy-based approach facilitates flexibility and adaptability as policies can be dynamically changed without modifying the underlying implementation. However, inconsistencies may arise in the policy specification. In this paper we provide a comprehensive set of QoS policies for managing Differentiated Services (DiffServ) networks, and classify the possible conflicts that can arise between them. We demonstrate the use of Event Calculus and formal reasoning for the analysis of both static and dynamic conflicts in a semi-automated fashion. In addition, we present a conflict analysis tool that provides network administrators with a user-friendly environment for determining and resolving potential inconsistencies. The tool has been extensively tested with large numbers of policies over a range of conflict types.

A reasoning agent for credit card fraud using the event calculus

We illustrate the design of an intelligent agent to aid a merchant to limit fraudulent payment card purchases over the internet. This is important because increasing fraud may limit the rise of electronic-commerce, and difficult because of the uncertainty in identifying and authenticating people remotely. The agent can advise the merchant what actions to take to reduce risk without complete knowledge of the circumstances. It can also negotiate flexibly to conclude transactions successfully that would otherwise be rejected. We use the event calculus to model the transaction system including the participants and their actions. The idea has applications in other distributed systems where incomplete knowledge of a system may be exploited by adversaries to their advantage.

Automating commonsense reasoning using the event calculus

Automating commonsense reasoning using the event calculus

Specifying norm-governed computational societies

Electronic markets, dispute resolution and negotiation protocols are three types of application domains that can be viewed as open agent societies. Key characteristics of such societies are agent heterogeneity, conflicting individual goals and unpredictable behavior. Members of such societies may fail to, or even choose not to, conform to the norms governing their interactions. It has been argued that systems of this type should have a formal, declarative, verifiable, and meaningful semantics. We present a theoretical and computational framework being developed for the executable specification of open agent societies. We adopt an external perspective and view societies as instances of normative systems. In this article, we demonstrate how the framework can be applied to specifying and executing a contract-net protocol. The specification is formalized in two action languages, the C + language and the Event Calculus, and executed using respective software implementations, the Causal Calculator and the Society Visualizer. We evaluate our executable specification in the light of the presented case study, discussing the strengths and weaknesses of the employed action languages for the specification of open agent societies.

Structured storage of legal precedents using a minimal deontic ontology, for computer assisted legal document querying

The automatic interpretation of case law, by computerised natural language processing algorithms, remains an elusive challenge. This paper proposes a less ambitious goal: human assisted semantic tagging of case law, using a basic deontic ontology, so that the structured document can be queried. Independent Resource Description Framework (RDF) named graphs are used to represent the legal case. An implementation of event calculus is used to make inferences over these named graphs. We employ our minimal deontic encoding to encode the significant aspects of a commercial case from the South African High Court.

Nonmonotonic abductive inductive learning

Inductive Logic Programming (ILP) is concerned with the task of generalising sets of positive and negative examples with respect to background knowledge expressed as logic programs. Negation as Failure (NAF) is a key feature of logic programming which provides a means for nonmonotonic commonsense reasoning under incomplete information. But, so far, most ILP research has been aimed at Horn programs which exclude NAF, and has failed to exploit the full potential of normal programs that allow NAF. By contrast, Abductive Logic Programming (ALP), a related task concerned with explaining observations with respect to a prior theory, has been well studied and applied in the context of normal logic programs. This paper shows how ALP can be used to provide a semantics and proof procedure for nonmonotonic ILP that utilises practical methods of language and search bias to reduce the search space. This is done by lifting an existing method called Hybrid Abductive Inductive Learning (HAIL) from Horn clauses to normal logic programs. To demonstrate its potential benefits, the resulting system, called XHAIL, is applied to a process modelling case study involving a nonmonotonic temporal Event Calculus (EC).

A New Approach for Discovering Business Process Models from Event Logs

Process mining is the automated acquisition of process models from the event logs of information systems. Although process mining has many useful applications, not all inherent difficulties have been sufficiently solved. A first difficulty is that process mining is often limited to a setting of non-supervised learnings since negative information is often not available. Moreover, state transitions in processes are often dependent on the traversed path, which limits the appropriateness of search techniques based on local information in the event log. Another difficulty is that case data and resource properties that can also influence state transitions are time-varying properties, such that they cannot be considered ascross-sectional.This article investigates the use of first-order, ILP classification learners for process mining and describes techniques for dealing with each of the above mentioned difficulties. To make process mining a supervised learning task, we propose to include negative events in the event log. When event logs contain no negative information, a technique is described to add artificial negative examples to a process log. To capture history-dependent behavior the article proposes to take advantage of the multi-relational nature of ILP classification learners. Multi-relational process mining allows to search for patterns among multiple event rows in the event log, effectively basing its search on global information. To deal with time-varying case data and resource properties, a closed-world version of the Event Calculus has to be added as background knowledge, transforming the event log effectively in a temporal database. First experiments on synthetic event logs show that first-order classification learners are capable of predicting the behavior with high accuracy, even under conditions of noise.

A Policy-Driven Service Composition Method for Adaptation in Pervasive Computing Environment

Service composition allows distributed application, such as multimedia application, to be composed from atomic service units and to adapt dynamically to users' requirements and environment conditions in pervasive computing system. It augments the adaptation action space for the application of pervasive computing. According to the multidimensional QoS (Quality of Service) requirement of pervasive computing system, we proposed a comprehensive service composition method to enhance the capability of application adaptation. First, according to a hierarchy policy model and a policy specification language, strengthened by event calculus, service discovery policy action integrating the situation of user, application, environment and resource can be triggered. Secondly, the proposed physical space model can support the location-aware service discovery and explicit range query to improve the efficiency of the query. To the end, an adaptation policy evaluation model is utilized to maximize an evaluation criterion–quality of satisfaction of users and environment by optimizing the optional service selection and the composition path. Through experiment and discussion of the algorithm, the paper further illustrates the great potential advantage of the solution to service composition.

The Processing Consequences of the Imperfective Paradox

In this paper we present a semantic analysis of the imperfective paradox based on the Event Calculus (van Lambalgen & Hamm 2004), a planning formalism characterizing a class of models which can be computed by connectionist networks. We report the results of a questionnaire that support the semantic theory and suggest that different aspectual classes of VPs in the progressive give rise to different entailment patterns. Further, a processing model is outlined, combining the semantic analysis with the psycholinguistic principle of immediacy in the framework of recurrent networks. The model is used to derive predictions concerning the electrophysiological correlates of the computations described by the Event Calculus.

Ramifications: An Extension and Correspondence Result for the Event Calculus

Classical logic Event Calculus, and the special purpose logical action language Formula, are both well established formalisms for describing actions and change. However, there is yet to be an account of ramifications in Event Calculus sufficiently general to represent the classes of domains expressible in Formula. Indeed, an adequately general ramification theory constructed in any general purpose logical language still awaits. Therefore, under the motivation of creating a flexible ramification theory in a universal language, suitable for integration into a rich action theory, a new enhanced version of classical logic Event Calculus named EC-R is proposed. EC-R supports representation and reasoning about domains containing ramifications for classes of domains more general than those possible under previous general purpose language formulations. This article makes two main contributions. The first, EC-R, is a narrative-based action formalism able to represent concurrent events, non-deterministic actions and indirect causal effects by virtue of an integrated solution to the frame and ramification problems. The formalism can reason about significant subclasses of domains containing both mutually interacting effects and cyclic causal dependencies. The formalism is elaboration tolerant and may be integrated with the standard variants of the Event Calculus. The second contribution is the definition of a semantic mapping between EC-R and Formula, and a proof of soundness and completeness of the EC-R theory with respect to Formula's model theoretic specification.

A Formal Framework for Web Services Coordination

Recently the term Web Services Choreography has been introduced to address some issues related to Web Services Composition and Coordination. Several proposals for describing Choreography for Business Processes have been presented in the last years and many of these languages (e.g. BPEL4WS) make use of concepts as long-running transactions and compensations for coping with error handling. However, the complexity of BPEL4WS makes it difficult to formally define this framework, thus limiting the formal reasoning about the designed applications. In this paper, we formally address Web Services Coordination with particular attention to Web transactions. We enhance our past work - the Event Calculus - introducing two main novelties: i) a multicast event notification mechanism, and ii) event scope names binding. The former enables an easier specification of complex coordination scenarios — such as E-commerce applications require — while the latter allows many new interesting behaviors which can be very useful in business scenarios: the introduction of private event scope names — used to deal with security and privacy — and a dynamic event scopes definition that can be used to manage multiple instances of the same application.

NON-INTRUSIVE MONITORING OF SERVICE-BASED SYSTEMS

This paper presents a framework for monitoring the compliance of systems composed of Web-services with requirements set for them at runtime. This framework assumes systems composed of Web-services which are co-coordinated by a service composition process expressed in BPEL and uses event calculus to specify the requirements to be monitored. These requirements may include behavioral properties of a system which are automatically extracted from the specification of its composition process in BPEL and/or assumptions that system providers can specify in terms of events extracted from this specification.

Event calculus and temporal action logics compared

We compare the event calculus and temporal action logics (TAL), two formalisms for reasoning about action and change. We prove that, if the formalisms are restricted to integer time, inertial fluents, and relational fluents, and if TAL action type specifications are restricted to definite reassignment of a single fluent, then the formalisms are not equivalent. We argue that equivalence cannot be restored by using more general TAL action type specifications. We prove however that, if the formalisms are further restricted to single-step actions, then they are logically equivalent.

Three problems in logic‐based knowledge representation

PurposeThe purpose of this article is to give a non‐technical overview of some of the technical progress made recently on tackling three fundamental problems in the area of formal knowledge representation/artificial intelligence. These are the Frame Problem, the Ramification Problem, and the Qualification Problem. The article aims to describe the development of two logic‐based languages, the Event Calculus and Modular‐E, to address various aspects of these issues. The article also aims to set this work in the wider context of contemporary developments in applied logic, non‐monotonic reasoning and formal theories of common sense.Design/methodology/approachThe study applies symbolic logic to model aspects of human knowledge and reasoning.FindingsThe article finds that there are fundamental interdependencies between the three problems mentioned above. The conceptual framework shared by the Event Calculus and Modular‐E is appropriate for providing principled solutions to them.Originality/valueThis article provides an overview of an important approach to dealing with three fundamental issues in artificial intelligence.

Ontology for human talk and thought (not robotics)

1. Introduction Hamm, Kamp, and van Lambalgen 2006 (hereafter HKL) propose to relate NL discourse to cognitive representations that also deal with world knowledge, planning, belief revision, etc. Their implementation involves translating NL discourse first into DRT, which explicates the linguistic information, and then into an event calculus, which uses world knowledge and non-monotonic reasoning to arrive at the final cognitive representation.

Formalizing the specification and execution of workflows using the event calculus

The event calculus is a logic programming formalism for representing events and their effects especially in database applications. This paper proposes the event calculus as a logic-based methodology for the specification and execution of workflows. It is shown that the control flow graph of a workflow specification can be expressed as a set of logical formulas and the event calculus can be used to specify the role of a workflow manager through a set of rules for the execution dependencies of activities. The proposed framework for a workflow manager maintains a history of events to control the execution of activities. The events are instructions to the workflow manager to coordinate the execution of activities. Based on the already occurred events, the workflow manager triggers new events to schedule new activities in accordance with the control flow graph of the workflow. The net effect is an alternative approach for defining a workflow engine whose operational semantics is naturally integrated with the operational semantics of a deductive database. Within this framework it is possible to model sequential and concurrent activities with or without synchronization. It is also possible to model agent assignment and execution of concurrent workflow instances. The paper, thus, contributes a logical perspective to the task of developing formalization for the workflow management systems.

Extending the event calculus for tracking epidemic spread

The email reporting system has been recognized as a key tool for early warning of disease outbreaks and surveillance of emerging diseases. The aim of the work reported here was to develop a formal language for building an event-centered representation of outbreak histories, described by outbreak reports, which could be used for tracking the spread of epidemics. The SpatioTemporal Extended Event Language (STEEL) we have built is an extension of the Event Calculus that is based on joint spatial and temporal location of event occurrences and structured conglomeration of events. This language allows us to represent and build aggregates of events, according to their spatiotemporal location. In a proof of concept study, this language was implemented in Prolog. A trial corpus of 35 outbreak reports from a PROMED-Mail diffusion list was hand coded in an experimental implementation of STEEL. The performances of this language were compared with three human experts during a question and answer task on this corpus. The experiment showed agreement between responses of the experts and the system. STEEL ensures the spatial and temporal location of event occurrence. The resulting representation is very close to the narrative. Further work must be made to develop a system capable of automatically modeling outbreak reports.

Merging news reports that describe events

Many kinds of news report provide information about events. For example, business news reports in the area of mergers and acquisitions, provide information about events such as “company X making a bid for company Y”, or “takeover of company Y by company X being rejected by the anti-trust authorities”. Furthermore, news reports do not normally exist in isolation. There is an underlying narrative which concerns a number of entities related in some way over a period of time. In many domains, stories will follow a stereotypical sequence. For example, a particular takeover may involve a bid being made, a rejection by the target board, a rise in the bid value by the potential buyer, a recommendation of acceptance by the target board, acceptance by the shareholders, and finally successful completion of the takeover. In order to merge heterogeneous news reports that describe events, we need to identify and reason about the events being described prior to merging them. In this paper, we investigate this problem with a focus on structured news reports. Each structured news report (SNR) is an XML document, where the textentries are restricted to individual words or simple phrases, such as names and domain-specific terminology, and numbers and units. We assume SNRs do not require natural language processing. As each SNR is isomorphic to a term in logic, we use a logic-based approach to extract relevant information about the events being described in the reports to be merged. We then provide a new version of the event calculus to assimilate the information from the various reports, to obtain the most up-to-date and complete picture of the events being described. Finally, from this assimilated information, we generate an SNR as the output.

USING THE EVENT CALCULUS FOR TRACKING THE NORMATIVE STATE OF CONTRACTS

In this work, we have been principally concerned with the representation of contracts so that their normative state may be tracked in an automated fashion over their deployment lifetime. The normative state of a contract, at a particular time, is the aggregation of instances of normative relations that hold between contract parties at that time, plus the current values of contract variables. The effects of contract events on the normative state of a contract are specified using an XML formalization of the Event Calculus, called ecXML. We use an example mail service agreement from the domain of web services to ground the discussion of our work. We give a characterization of the agreement according to the normative concepts of obligation, power and permission, and show how the ecXML representation may be used to track the state of the agreement, according to a narrative of contract events. We also give a description of a state tracking architecture, and a contract deployment tool, both of which have been implemented in the course of our work.