A logic programming framework for modeling temporal objects

Published versio

Some examples formulated in a ‘seeing to it that’ logic: Illustrations, observations, problems

The paper presents a series of small examples and discusses how they might be formulated in a ‘seeing to it that ’ logic. The aim is to identify some of the strengths and weaknesses of this approach to the treatment of action. The examples have a very simple temporal structure. An element of indeterminism is introduced by uncertainty in the environment and by the actions of other agents. The formalism chosen combines a logic of agency with a transition-based account of action: the semantical framework is a labelled transition system extended with a component that picks out the contribution of a particular agent in a given transition. Although this is not a species of the stit logics associated with Nuel Belnap and colleagues, it does have many features in common. Most of the points that arise apply equally to stit logics. They are, in summary: whether explicit names for actions can be avoided, the need for weaker forms of responsibility or ‘bringing it about ’ than are captured by stit and similar logics, some common patterns in which one agent’s actions constrain or determine the actions of another, and some comments on the effects that level of detail, or ‘granularity’, of a representation can have on the properties we wish to examine.

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 formalisation 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 characterisation 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.

The logic of unwitting collective agency

The paper is about the logic of expressions of the form `agent x brings it about that A is the case', or `agent x is responsible for its being the case that A', or `the actions of agent x are the cause of its being the case that A'. Agents could be deliberative (human or computer) agents, purely reactive agents, or simple computational devices. The `brings it about' modalities are intended to express unintentional, perhaps even accidental, consequences of an agent's actions, as well as possibly intentional (intended) ones. Since we make no assumptions at all about the reasoning or perceptual capabilities of the agents we refer to this form of agency as `unwitting'; unwitting can mean both inadvertent and unaware. The semantical framework is a form of labelled transition system extended with an extra component that picks out the actions of a particular agent in a transition, or its `strand' as we call it. We de ne a modal language for talking about the actions of individual agents or groups of agents in transitions, including two de ned modalities of the (unwitting) `brings it about' kind. The novel feature is the switch of attention from talking about an agent's bringing it about that a certain state of a airs exists to talking about an agent's bringing it about that a transition has a certain property. The middle part of the paper presents axiomatisations of the logic, and comments on relationships to other work, in particular on resemblances to P orn's (1977) logic of `brings it about'. The last part is concerned with characterisations of (unwitting) collective agency, that is, the logic of expressions of the form `the set G of agents, collectively though perhaps unwittingly, brings it about that A'

(C+)++: An action language for modelling norms and institutions

The language C+ of Giunchiglia, Lee, Lifschitz, McCain, and Turner (2004) is a formalism for specifying and reasoning about the e ects of actions and the persistence (`inertia') of facts over time. An `action description' in C+ is a set of C+ laws which de ne a labelled transition system of a certain kind. This document presents (C+)++, an extended form of C+ designed for representing norms of behaviour and institutional aspects of (human or computer) societies. There are two main extensions. The rst is a means of expressing `counts as' relations between actions, also referred to as `conventional generation' of actions. The second is a way of specifying the permitted (acceptable, legal) states of a transition system and its permitted (acceptable, legal) transitions

Computer support for protocol-based treatment of cancer

Cancer treatment is often carried out within protocol-based clinical trials. An oncology clinic may take part in many trials each of which requires data to be collected for monitoring efficacy and toxicity of treatment. Subsequently, this data is analysed statistically to evaluate clinical objectives of the trial. To be scientifically valid, such analysis must be based on data that is both complete and correct. This is one motivating factor for introducing computer support for trial management. Further motivation is provided by concern that treatment is consistent with the protocol and the well-being of the patient. The complexity of many protocols, the life-threatening nature of cancer and the toxicity of treatment side-effects emphasise the safety-critical nature of oncology. The OaSiS system provides decision support for the protocol-based treatment of cancer patients with emphasis on the safety aspects of the advice it gives. It offers a highly graphical interface, employs integrity constraint checking techniques from logic databases to monitor compliance with a protocol and is implemented in PROLOG. The paper describes the main features of OaSiS and indicates work in progress and planned. 1