Object-oriented Formalism Research Articles

STRPLAN: A Distributed Planner for Object-Centred Application Domains

This paper deals with the problem of constructing valid planning models as well as efficient planning techniques for multi-agent domain applications. For these purposes, we first introduce an object-oriented formalism that allows for a fully-structured description of all the elements of a planning theory. This formalism is intended to facilitate the acquisition, maintenance and re-use of the domain knowledge. The proposed formalism also serves as the basis for identifying useful structural domain properties. Afterwards, we introduce a new efficient multi-agent distributed planner, STRPLAN, specially suited for these models. STRPLAN relies on the concept of domain region, which takes into consideration the structural domain properties as well as the interference of actions. As a result, global plans can be decomposed into local linear plans as a function of these regions. Preliminary empirical results have shown that the presented approach is very efficient for highly-structured multi-agent domains. In this way, the proposed methodology provides a practical framework to treat large multi-agent domain applications.

An object-oriented descriptive language to facilitate advanced handwritten form processing

This paper presents an object-oriented form description language which has been developed to enhance the performance and flexibility of advanced form reader systems. The paper also outlines the structure of a form reader which would allow the language's capabilities to be fully utilised. The form description language presented here is novel in two ways: firstly, it allows the comprehensive utilisation of contextual information; and secondly, it enables the storage of form models which economically describe the logical and layout variations in the form design which are allowed for a particular class of form.

Knowledge acquisition issues in the design of decision support systems in quality control

Implementation of formal quality policy in manufacturing environments requires extensive knowledge in many different fields: (1) knowledge of the problems that can be found; (2) knowledge of the methods and procedures that can definitively improve the process; (3) knowledge of the quality techniques that can be used; and (4) how to implement these techniques in manufacturing environments. Different experts are able to provide such knowledge, ranging from operators to quality engineers which for example provide knowledge about specialised quality tools. Intelligent decision support systems (DSS) can be used to make quality expertise available to people who face quality problems every day. However, these systems are difficult to elaborate especially due to the acquisition and modelling tasks, considered as the bottleneck of intelligent systems development. Based on our experience of DSS development in the quality area, we propose here to analyze and classify the knowledge necessary to develop advisory systems for quality applications (e.g. process diagnosis, selection of quality tools and configuration of quality tools). Elicitation methods which have been proved successful for extracting quality knowledge are presented as well as guidelines for the design of acquisition sheets. Then we propose to describe the subsets of knowledge in a unified structure, which can be further implemented by the use of object-oriented formalism and rules. The structure greatly facilitates the design of advisory quality systems in manufacturing environments.

Using multi-agent architecture in FMS for dynamic scheduling

The proposed scheduling strategy is based on a multi-agent architecture. Each agent of this architecture is dedicated to a work centre (i.e. a set of resources of the manufacturing system); it selects locally and dynamically the most suitable dispatching rules. Depending on local and global considerations, a new selection is carried out each time a predefined event occurs (for example, a machine becomes available, or a machine breaks down). The selection depends on: (1) primary and secondary performance objectives, (2) the operating conditions, and (3) an analysis of the system state, which aims to detect particular symptoms from the values of certain system variables. We explain how the scheduling strategy is shared out between agents, how each agent performs a local dynamic scheduling by selecting an adequate dispatching rule, and how agents can coordinate their actions to perform a global dynamic scheduling of the manufacturing system. Each agent can be implemented through object-oriented formalisms. The selection method is improved through the optimization of the numerical thresholds used in the detection of symptoms. This approach is compared with the use of SPT, SIX, MOD, CEXSPT and CR/SPT on a jobshop problem, already used in other research works. The results indicate significant improvements.

Part-whole relations in object-centered systems: An overview

Knowledge bases, data bases and object-oriented systems (referred to in the paper as Object-Centered systems) all rely on attributes as the main construct used to associate properties to objects; among these, a fundamental role is played by the so-called part-whole relation. The representation of such structural information usually requires particular semantics together with specialized inference and update mechanisms, but rarely do current modelling formalisms and methodologies give it a specific, ‘first-class’ dignity. The main thesis of this paper is that the part-whole relation cannot simply be considered as an ordinary attribute: its specific ontological nature requires to be understood and integrated within data-modelling formalisms and methodologies. On the basis of such an ontological perspective, we survey the conceptual modelling issues involving part-whole relations, and the various modelling frameworks provided by knowledge representation and object-oriented formalisms.

Computational Driver Model in Transport Engineering: COSMODRIVE

With regard to road safety issues, a deep understanding of the driver as a logic system is crucial to predict the most probable behavior according to the contextual elements. Knowledge and data about human functional abilities exist. But the problem is to organize and structure them. The development of a computational approach in driver modelization is addressed. In the first part, a brief historical overview is presented of available driver models in ergonomics and psychological areas, and the distinction between predictive and explicative models in an implementation perspective is the focus. In the second part, the computational aspect of the work is described, along with the software concepts, the cognitive modeling needs, and the implementation choices. Object-oriented techniques were chosen because they provide a modular overview of the general system and offer a convenient representation of cognitive processes. Object-oriented formalism, in particular object modeling technique diagrams, acts as a bridge between the two domains of computer science and the human sciences. The objective is to determine whether it is possible to implement reliably a driver model using the techniques from artificial intelligence and based on the theoretical knowledge from cognitive sciences research. This attempt to establish links between different scientific domains, requiring a common tool, is a challenge. A first step of a work that will have to be developed in a long-term time scale, taking into account its quite ambitious objective, is described.

Computational Driver Model in Transport Engineering: COSMODRIVE

With regard to road safety issues, a deep understanding of the driver as a logic system is crucial to predict the most probable behavior according to the contextual elements. Knowledge and data about human functional abilities exist. But the problem is to organize and structure them. The development of a computational approach in driver modelization is addressed. In the first part, a brief historical overview is presented of available driver models in ergonomics and psychological areas, and the distinction between predictive and explicative models in an implementation perspective is the focus. In the second part, the computational aspect of the work is described, along with the software concepts, the cognitive modeling needs, and the implementation choices. Object-oriented techniques were chosen because they provide a modular overview of the general system and offer a convenient representation of cognitive processes. Object-oriented formalism, in particular object modeling technique diagrams, acts as a bridge between the two domains of computer science and the human sciences. The objective is to determine whether it is possible to implement reliably a driver model using the techniques from artificial intelligence and based on the theoretical knowledge from cognitive sciences research. This attempt to establish links between different scientific domains, requiring a common tool, is a challenge. A first step of a work that will have to be developed in a long-term time scale, taking into account its quite ambitious objective, is described.

Objects, agents and work flow modelling for concurrent engineering process design

Concurrent process engineering is concerned with the integration of traditionally separate individual activities in process design covering process, mechanical, civil and control phases, so that all life-cycle issues including safety, environmental impact, cost, operability and commissioning can be considered as early as possible in establishing manufacturing process. It seeks to enable multi-disciplinary teams, sometimes working at different sites to work cooperatively. The approach can be envisaged at three levels of conceptualisation related to design objects (process plants), design teams and a project manager, who controls the work flow among the teams. The life-cycle data of the design objects can be represented in a multi-dimensional object-oriented format using STEP/EXPRESS, while project teams are modelled by agents which provide tools for the specialist groups and carry out high level operations of application tools. Coordination of the agents depends on modelling the work flow so as to control concurrent activity and sequencing of sub tasks.

Object-oriented query language access to relational databases: A semantic framework for query translation

This research investigates and approach to query processing in a multidatabase system that uses an objectoriented model to capture the semantics of other data models. The object-oriented model is used to construct a global schema, defining an integrated view of the different schemas in the environment. The model is also used as a self-describing model to build a meta-database for storing information about the global schema. A unique aspect of this work is that the object-oriented model is used to describe the different data models of the multidatabase environment, thereby extending the meta database with semantic information about the local schemas. With the global and local schemas all represented in an object-oriented form, structural mappings between the global schema and each local schema are then easily supported. An object algebra then provides a query language for expressing global queries, using the structural mappings to translate object algebra queries into SQL queries over local relational schema. The advantage of using an object algebra is that the object-oriented database can be viewed as a blackboard for temporary storage of local data and for establishing relationships between different databases. The object algebra can be used to directly retrieve temporarily-stored data from the object-oriented database or to transparently retrieve data from local sources using the translation process described in this paper.

Distributed environment: A conceptual framework using objects

We present a conceptual framework for a distributed office system using concepts inherent to object-oriented formalism. The functions of the active object and the procedure servers are described. So are the attributes of the objects stored in these two servers. In order to endow the individual workstations with as much autonomy as possible, we develop a coarse-grained algorithm for active and procedural object distribution. An office model should have a high level of evolvability. To accommodate this phenomenon we devise a mechanism to enable the model to transit one state to another with a minimum level of perturbation.

APPLICATION MODELLING IN HETEROGENEOUS ENVIRONMENTS USING AN OBJECT SPECIFICATION LANGUAGE

We propose an object-oriented logical formalism to conceptionally model applications in an interoperable environment. Such an environment consists of heterogeneous and autonomous local (database) systems. Applications in such an environment use several resources and services. Their conceptual modelling involves re-specification of existing systems in terms of homogeneous views, modelling of behavior and system dynamics, modelling of logically distributed components in an open environment and the modelling of communication relationships and dependencies between components. We introduce a formal object-oriented language capable of dealing with these requirements and illustrate its use to model applications in an interoperable environment.

Discrete-event simulation of forest landscape response to fire disturbances

The objective of this work is to illustrate the potential of discrete-event simulation methodologies and object-oriented hierarchical models to simulate landscape dynamics. We formalized the Noble and Slatyer vegetation replacement scheme in a mdular, object-oriented formalism to simulate vegetation dynamics. Based on this module, we suggest a framework for simulating vegetation dynamics in spatially complex landscape systems composed of interacting patches. As illustrated with the simulations performed for a two-patch landscape, patch components are organized in a hierarchical structure, with information flow in the form of messages passing among the hierarchically arranged components. System behavior can be analyzed from any level of organization. Finally, we briefly discuss the implementation of this framework in a Geographic Information System.

A database for diverse power system simulation applications

The authors describe a database capable of supporting a diverse set of power system simulation applications ranging from harmonics and transient analysis to conventional load flow and short-circuit calculations. The wide range of applications requires that the data be modeled in a more basic, or lower-level, form than is required for many traditional power system analysis programs. The need for the database, the design objectives, and the evolution of the design are described. A strictly relational database was attempted at first. Difficulties in modeling complex data structures resulted in changing the database to a more object-oriented form. Several of the key data structures are presented as well as typical programming techniques for accessing the database.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Knowledge Based System and Database Management System

Knowledge based management systems has gained significant importance in the last few years, primarily from the enhanced capabilities achieved through integration of the two technologies - artificial intelligence and database management systems. This paper develops a framework for integrating the two technologies. The three dimensional framework links the various knowledge representation schemes with the data models used in databases and the architectures used for linking the knowledge base with the database system. This framework facilitates in communicating the latest developments in the field of knowledge based management systems and also aids the designer in making the appropriate choice from the various options available within the two technologies. The research systems in the field are mapped onto the framework. An analysis of the mapping reveals that some research areas are more popular than others. Rule-based knowledge representation with loose coupling to relational databases are found to be popular for integrating the two systems. Integrated solutions with object-oriented formalisms are also becoming common in recent years. Potential areas for future research are identified. Also, the implications of the research for the practitioner and the strategies for commercial exploitation of KBMS are discussed.

Temporal representation of clinical algorithms using expert-system and database tools

The HyperLipid Advisory System combines a rule-based implementation of a clinical algorithm (the NIH Cholesterol Education Program Expert Panel recommendations) with a temporal representation that facilitates reasoning over time while maintaining efficient storage in a standard database. The temporal representation consists of objects that model point events such as visits and interval events such as specific therapies. These objects are combined into abstractions called phases, which correspond to higher level clinical concepts such as a diet or drug treatment. The time-oriented data objects are referenced in the rules using a custom-tailored operator query language. Between user sessions relevant clinical data are stored in external files. When the advisory system is reconsulted, this information is retrieved and mapped back into an object-oriented format. Use of a commercially available expert-system shell for such tasks allows algorithm implementation in standard personal computing environments.

Time warp operating system

This paper describes the Time Warp Operating System, under development for three years at the Jet Propulsion Laboratory for the Caltech Mark III Hypercube multi-processor. Its primary goal is concurrent execution of large, irregular discrete event simulations at maximum speed. It also supports any other distributed applications that are synchronized by virtual time. The Time Warp Operating System includes a complete implementation of the Time Warp mechanism, and is a substantial departure from conventional operating systems in that it performs synchronization by a general distributed process rollback mechanism. The use of general rollback forces a rethinking of many aspects of operating system design, including programming interface, scheduling, message routing and queueing, storage management, flow control, and commitment. In this paper we review the mechanics of Time Warp, describe the TWOS operating system, show how to construct simulations in object-oriented form to run under TWOS, and offer a qualitative comparison of Time Warp to the Chandy-Misra method of distributed simulation. We also include details of two benchmark simulations and preliminary measurements of time-to-completion, speedup, rollback rate, and antimessage rate, all as functions of the number of processors used.