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Temporal Representation and Reasoning, 1997. (TIME '97), Proceedings., Fourth International Workshop on

Date 10-11 May 1997

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  • Proceedings of TIME '97: 4th International Workshop on Temporal Representation and Reasoning

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    Freely Available from IEEE
  • Index of authors

    Page(s): 187
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    Freely Available from IEEE
  • Contingent durations in temporal CSPs: from consistency to controllabilities

    Page(s): 78 - 85
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    Temporal Constraint Networks (TCSP) allow to express minimal and maximal durations between time-points. Though being used in many research areas, this model disregards the contingent nature of some constraints, whose effective duration cannot be decided by the system but is provided by the external world. We propose an extension of TCSP in which the classical network consistency property must be redefined in terms of controllability: intuitively, we would like to say that a network is controllable if it is consistent in any situation (i.e. any assignment of the whole set of contingent intervals) that may arise in the external world. Three levels of controllability must be distinguished, namely the Strong, the Weak and the Dynamic ones. This preliminary report mainly stresses the representation and concept issues, discussing their relevance in dynamic application domains, and partially tackles the reasoning issues (complexity, algorithms and tractable subclasses) View full abstract»

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  • Temporal control structures in expert critiquing systems

    Page(s): 160 - 167
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    Critiquing in time critical and resource constrained domains requires special control structures that allow the expert critiquing system to compare user actions with that of its own. This is necessitated by the fact that the priorities of actions in such domains change over time and the system needs to be robust enough to reflect this in its critiques. This paper describes a model of expert critiquing where the use of blackboard architectures, temporal control structures and data manipulation and differential critiquing are effectively combined to tackle this issue. The proof-of-principal critiquing domain is novice experts training in the area of Ship Damage Control View full abstract»

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  • Temporal reasoning with fuzzy time-objects

    Page(s): 128 - 135
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    A novel approach to temporal reasoning is proposed which deals with both uncertain facts and uncertain temporal information in fuzzy logic. Fuzzy time-objects are defined to represent these uncertainties. A point of particular concern when reasoning with both kinds of uncertainty is that temporal uncertainty should not influence factual uncertainty. On the other hand temporal reasoning is exactly about the relation between time and fact. By introducing constrained time-objects we show that a relation between time and fact can be established while avoiding mixing of uncertainties. Then a method to reason with time-objects is introduced. The inference relation between time-objects is thereby decomposed in a fact-fact and a time-time relation. Such a decomposition is only allowed for (semi-) separable time-objects. The decomposition does not prevent time and fact to have mutual influence View full abstract»

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  • Qualitative and quantitative temporal constraints about numerically quantified periodic events

    Page(s): 94 - 101
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    The paper describes an integrated temporal formalism which deals with (i) quantitative information about the frame of time and the user-defined calendar-dates (periods) in which periodic events are located, (ii) (possibly multiple) numeric quantifiers indicating the number of repetitions of events and (iii) qualitative relations between periodic events. The paper defines the operations of intersection and composition of temporal specifications in the given formalism, which are used in order to perform temporal reasoning. An algorithm supporting specialised forms of reasoning about the number of repetitions of events is also described. Moreover, the paper introduces an expressive query language for extracting different types of temporal constraints from a knowledge base of temporal specifications in the formalism, sketching the reasoning algorithms needed to answer the queries View full abstract»

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  • Representation of continuous change with discrete time

    Page(s): 175 - 179
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    In this paper we study one of the drawbacks that have been considered against the use of discrete time in Temporal Reasoning Systems, which is the difficulty to represent continuous change. We study the representation of continuous change for the particular case of a constraint solver over integers. We have used two different approaches. The first approach using the concept of error and the second one using the concept of granularity View full abstract»

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  • A hierarchy for convex relations

    Page(s): 86 - 93
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    This paper is concerned with a hierarchical representation of the convex relation algebra, which is a computationally tractable subset of Allen's interval calculus. The hierarchy of convex relations is used to determine the minimal point relation constraints which hold between the end points of the intervals. Nine convex relations are proven to be special, because they introduce new constraints. One intended application of this hierarchy is a natural language discourse processing system. A more precise specification for the temporal constraints derivable by the discourse grammar due to Lascarides and Asher (1993) is given View full abstract»

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  • Similarity of event sequences

    Page(s): 136 - 139
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    Sequences of events are an important form of data that occurs in many application domains, such as telecommunications, biostatistics, user interface design, etc. We present a simple model for measuring the similarity of event sequences, and show that the resulting measure of distance can be efficiently computed using a form of dynamic programming View full abstract»

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  • A resolution method for CTL branching-time temporal logic

    Page(s): 20 - 27
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    We extend our clausal resolution method for linear temporal logics to a branching-time framework. The branching-time temporal logics considered are computation tree logic (CTL), often regarded as the simplest useful logic of this class, and extended CTL (ECTL), which is CTL extended with fairness operators. The key elements of the resolution method, namely the normal form, the concept of step resolution and a novel temporal resolution rule, are introduced and justified with respect to both these logics. A completeness argument is provided, together with an example of the use of the temporal resolution method. Finally, we consider future work, in particular extension of the method yet further, to CTL*, and implementation of the approach by utilising techniques developed for linear-time temporal resolution View full abstract»

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  • Representing temporal relationships between events and their effects

    Page(s): 148 - 152
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    Temporal relationships between events and their effects are complex. As the effects of a given event, a proposition may change its truth value immediately after the occurrence of the event and remain true until some other events occur, while another proposition may only become true/false from some time after the causal event has occurred. Expressing delayed effects of events has been a problematic question in most existing theories of action and change. This paper presents a new formalism for representing general temporal causal relationships between events and their effects. It allows expressions of both immediate and delayed effects of events, and supports common-sense assertions such as “effects cannot precede their causes” View full abstract»

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  • An efficient algorithm for temporal abduction

    Page(s): 28 - 30
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    Abduction is the process of generating explanations for an observation, starting from a domain theory. We consider an extension of the classical definition of abduction in order to deal with temporal knowledge both in the theory and in the observations. This form of abduction is the basis of many problem solving activities such as temporal diagnosis and reasoning about actions and events. We show how the locality property can be used in order to compute temporal explanations efficiently. In fact, they could be computed using first an abductive reasoner as a generator of candidates and then a temporal reasoner for checking the consistency of each candidate View full abstract»

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  • Enhancements to the Ground Processing Scheduling System

    Page(s): 72 - 77
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    This paper describes work in progress to enhance the performance of the Ground Processing Scheduling System (GPSS). The GPSS is a constraint-based scheduler that deals with three kinds of constraints: temporal, resource, and configuration. It starts with a complete schedule that may have some constraint violations (conflicts) and gradually improves the schedule by reducing the violations. The objective is to optimize the schedule in terms of constraint violations and resource utilization. The enhancement is accomplished by improving heuristics currently used for constraint satisfaction and adding an extra feature which we call fencing. Fencing allows for obtaining a conflict-free sub-schedule within a selected period of time View full abstract»

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  • Automata representations for Concurrent METATEM

    Page(s): 12 - 19
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    Concurrent METATEM is a language based on the execution of temporal logic formulae. The current implementations are based upon direct interpretation, yet are too slow for large applications. We present an approach to implementing the language by representing temporal formulae as finite-state automata. To combat the problems associated with constructing a single automaton containing all possible models of a formula, we partition the representation into three closely coupled automata. This provides structures small enough to be effectively used for larger applications, while still allowing increased performance over the direct interpretation of temporal formulae View full abstract»

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  • Time in a multi-theory logical framework

    Page(s): 62 - 68
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    We present a knowledge representation framework where a collection of logic programs can be combined together by means of meta-level program composition operations. Each object-level program is composed by a collection of extended clauses, equipped with a time interval representing the time period in which they hold. The interaction between program composition operations and time yields a powerful knowledge representation language in which many applications can be naturally developed. The language is given a meta-level semantics which provides also an executable specification. Two applications in the field of business regulations are shown View full abstract»

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  • Entities and relations for historical relational databases

    Page(s): 180 - 186
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    Research to extend models of data to handle the temporal dimension has been conducted mainly in the context of the relational data model. In the relational model, the primary object of database design, manipulation and retrieval is the relation, viewed extensionally as a finite set of tuples. This paper proposes three useful types of temporal entities: events, histories, and valid-time relations, and defines relations and operations which allow for patterns of ordering and duration information to be defined and extracted. These patterns can often be expressed as select conditions on temporal relations in an algebraic query language. This paper is both a survey of existing trends in temporal database research, and a refinement of the conceptual framework used to characterize temporal information View full abstract»

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  • GCH-OSQL: a temporally-oriented object-oriented query language based on a three-valued logic

    Page(s): 119 - 126
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    The need of managing temporal information given at different levels of granularity and indeterminacy is common to many application areas. Between them, we focus on the management of clinical data. Different time granularities are also needed in querying temporal databases. In this paper, we describe GCH-OSQL (Granular Clinical History-Object Structured Query Language), an object-oriented temporally-oriented extension of SQL. GCH-OSQL is based on an object-oriented temporal data model, named GCH-OODM. GCH-OODM allows storage of temporal information at different and mixed granularities. GCH-OSQL deals with the valid time of temporal data. The temporal extension of the SELECT statement includes the addition of the TIME-SLICE and MOVING WINDOW clauses, and the capability of referring to the temporal dimension of objects in the WHERE and SELECT clauses View full abstract»

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  • A structured framework for representing time in a generative composition system

    Page(s): 168 - 174
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    The representation of music structures is, from Musicology to Artificial Intelligence, a widely known research focus. It entails several generic Knowledge Representation problems like structured knowledge representation, time representation and causality. In this paper, we focus the problem of representing and reasoning about time in the framework of a structured music representation approach, intended to support the development of a Case-Based generative composition system. The basic idea of this system is to use Music Analysis as foundation for a generative process of composition, providing a structured and constrained way of composing novel pieces, although keeping the essential traits of the composer's style. We propose a solution that combines a tree-like representation with a pseudo-dating scheme to provide an efficient and expressive means to deal with the problem View full abstract»

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  • Temporal resolution: removing irrelevant information

    Page(s): 4 - 11
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    The generation of too much information prohibits efficient resolution proof search in classical logics. Hence subsumption is used to discard redundant information and strategies have been developed to guide the proof search avoiding irrelevant information. The extension of the resolution method to temporal logics, for example that by Fisher (1991) for propositional linear-time temporal logics, further magnifies this problem. We provide an algorithm to efficiently remove irrelevant information prior to the application of Fisher's temporal resolution rule, show that it retains the completeness of the temporal resolution system and demonstrate its efficiency on a set of examples View full abstract»

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  • BCTL: a branching clock temporal logic

    Page(s): 140 - 147
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    This paper presents a branching time temporal logic called BCTL. In this logic, branching time is represented by branching clocks, which can be specified as Chronolog programs. In BCTL, formulas are allowed to be defined on different branching clocks. Apart from the temporal operators first and next, BCTL contains a next-bounded symbol ! and four modalities: ∀□, ∀?, ∃□ and ∃?. This logic can be used to describe nondeterministic programs and concurrent systems View full abstract»

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  • Knowledge-based temporal interpolation

    Page(s): 102 - 111
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    Temporal interpolation is the task of bridging gaps between time-oriented concepts in a context-sensitive manner. It is a subtask important for solving the temporal-abstraction task-abstraction of interval-based, higher-level concepts from time-stamped data. We present a knowledge-based approach to the temporal-interpolation task and discuss in detail the precise knowledge required by that approach, its theoretical foundations, and the implications of the approach. The temporal-interpolation computational mechanism we discuss relies, among other knowledge types, on a temporal-persistence model. The temporal-persistence model employs local temporal-persistence functions that are temporally bidirectional (i.e., extend a belief measure in a predicate both into the future and into the past) and global, maximal-gap temporal-persistence functions that bridge gaps between interval-based predicates. We investigate the quantitative and qualitative properties implied by both types of persistence functions. We have implemented our approach and evaluated it in several different domains. We discuss its implications for acquisition, maintenance, reuse, and sharing of temporal-abstraction knowledge View full abstract»

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  • On effective data clustering in bitemporal databases

    Page(s): 54 - 61
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    Temporal databases provide built-in supports for efficient recording and querying of time-evolving data. In this paper, data clustering issues in temporal database environment are addressed. Data clustering is one of the most effective techniques that can improve performance of a database system. However, data clustering methods for conventional databases do not perform well in temporal databases because there exist crucial differences between their query patterns. We propose a data clustering measure, called Temporal Affinity, that can be used for the clustering of temporal data. The temporal affinity, which is based on the analysis of query patterns in temporal databases, reflects the closeness of temporal data objects in viewpoints of temporal query processing. We perform experiments to evaluate the proposed measure. The experimental results show that a data clustering method with the temporal affinity works better than other methods View full abstract»

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  • Modal event calculi with preconditions

    Page(s): 38 - 45
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    Kowalski and Sergot's (1986) event calculus (EC) is a simple temporal formalism that, given a set of event occurrences, allows the derivation of the maximal validity intervals (MVIs) over which properties initiated or terminated by those events hold. The limited expressive power of EC is notably augmented by permitting events to initiate or terminate a property only if a given set of preconditions hold at their occurrence time. We define a semantic formalization of the event calculus with preconditions. We gain further expressiveness by considering modal variants of this formalism, and show how to adapt our semantic characterization to encompass the additional operators. We discuss the complexity of MVI validation and describe examples showing that modal event calculi with preconditions can be successfully exploited to deal with real-world applications View full abstract»

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  • Practical temporal reasoning for real scheduling applications

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    Summary form only given. Presents a set of requirements for modelling and solving scheduling problems, including a somewhat unconventional definition of the term “solution”. These requirements, distilled from experience implementing and fielding scheduling systems in a wide variety of domains, strongly constrain the nature of a useful scheduling system. Using a set of example problems drawn from this experience, the author motivates and explicates an approach to temporal reasoning for scheduling in which the system dynamics encoded in the temporal representation are “convex”, in the sense that all disjunction is treated as a range, rather than as a set of discrete points or regions of feasibility. Non-convex disjunction is encoded explicitly in a set of variables, such that finding a complete assignment to the set of variables is equivalent to constructing a feasible schedule. The problem is then solved as a Constraint Satisfaction Problem. Finally, the author discusses some recent extensions of this work, applying the same approach to problems involving a more complex system dynamic View full abstract»

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  • Visual query operators for temporal databases

    Page(s): 46 - 53
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    Many recent proposals in the literature present easy-to-use query languages, based on visual representations of the database and direct manipulation mechanisms. Such proposals essentially deal with conventional query operations, whereas little effort is devoted to investigate friendly environments for querying temporal databases. Nevertheless, temporal aspects are generally considered extremely relevant in several database applications. Thus, the various users should be provided with powerful and simple query systems also exhibiting temporal features. While attempting to meet this need, we propose a visual query system for temporal databases. It adopts a diagrammatic representation of the database schema (including temporal classes and relationships), on which conventional as well as temporal visual query operators can be applied. In this paper we concentrate on the temporal operators, showing both examples of usage and formalization View full abstract»

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