Object-oriented Data Research Articles

Combining active rules and metaclasses for enhanced extensibility in object-oriented systems

This paper is concerned with techniques for supporting extensibility in object-oriented data models. It has been recognised for a number of years that, in systems which support metaclasses as first-class objects, extensibility can be achieved by using specialisation to refine built-in object creation behaviour. At the same time, research into active rules has indicated the utility of mapping high-level descriptions of functionality onto active rules for evaluation. This paper proposes the integration of these two techniques, arguing that certain constructs which would be difficult to represent using either one alone can be supported effectively by a judicious mixing of the two.

Model/heuristic-based alarm processing for power systems

This paper describes an intelligent alarm processing expert system which is integrated in a large Supervisory Control and Data Acquisition system for power distribution networks. The expert system works as an operator support tool by diagnosing network disturbances and device malfunctions. The expert system is based on a hierarchic, multi-level problem-solving architecture, integrating both model-based and heuristic techniques acting upon an object-oriented data structure. Several enhancements have been designed and implemented to enable the system to perform its task online and real-time. The expert system covers online processing of real-time data and intelligent alarm processing, as well as the automatic creation and update of the knowledge base. It consists of approximately 25000 objects (units) and 190 rules. The system uses the expert system tool KEE, runs on SUN workstations, and is integrated in the Supervisory Control and Data Acquisition system via LAN. The expert system was implemented for the Public Utilities Board Singapore controlling its 22 kV distribution network and has been online since November 1990.

A novel architecture for handling persistent objects

The storage and processing of persistent objects presents opportunities for add-on hardware support. Particularly, there are aspects of memory management and whole-structure processing which are seen to benefit from a novel kind of SIMD-parallel architecture. This paper discusses the top-down requirements for handling persistent objects and then describes an active memory unit called the IFS/2 which meets these requirements. Performance figures for prototype hardware are given, and its application to an object-oriented data model is briefly described.

A visual query language for graphical interaction with schema-intensive databases

This paper presents a visual query language called VQL for interacting with an object-oriented schema-intensive data model. VQL allows convenient access to the various types of knowledge captured by the semantic model. It consists of a set of "graphical primitives" along with a combination grammar for creating graphical queries. The visual language is internally supported by a prolog-like predicate based query language. The formal grammar underlying the predicate based language is also presented. Apart from being able to create simple queries that can be specified in SQL or QBE, VQL can be used for making queries on any object-oriented data model including the generalization of the E-R model. VQL also handles complicated, indirect queries, specially those that require a reasoning system for query interpretation and response generation. Further, recursive queries on graph structures such as finding transitive closures of graphs may be easily specified. Perhaps the most powerful feature of VQL is its ability to provide high semantic expressibility (in being able to specify highly complex queries) while maintaining simplicity in the user's query formulation process. VQL is embedded in an object-oriented graphical database interaction environment that supports schema creation and manipulation in addition to database querying and updation. The prototype has been implemented in Smalltalk-80 running on a Sun 3/60 workstation. All the illustrations of visual interaction presented are taken from actual interaction sessions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On-line expert system for power system diagnosis and restoration

We have implemented a real-time expert system as part of a supervisory control and data acquisition system for the Public Utilities Board of Singapore, controlling its 22 kV distribution network. It works as an operator support tool by diagnosing network disturbances and device malfunctions, and by presenting a switching sequence which can be executed immediately to restore supply. In this paper we describe how the expert system is integrated into a large supervisory control and data acquisition system for power distribution networks. The necessary techniques to cover on-line processing of real-time data, intelligent alarm processing and network reconfiguration/restoration are discussed. The expert system is based on a hierarchic multi-level problem-solving architecture, integrating model-based, heuristic and algorithmic techniques acting on an object-oriented data structure. Techniques such as the automatic creation and update of the knowledge base, event filtering, on-line event processing, and structural and temporal focusing have been implemented to enable the system to perform its task on-line and in real time.

The object-oriented data structures course

The object-oriented data structures course

An object-oriented simulation environment for airbase logistics

The subject of this paper, the Integrated Model Development Environment (IMDE), addresses basic difficulties experienced in simulating airbase logistics. These difficulties arise during two major modeling activities: 1) developing the conceptual model, and 2) translating the conceptual model to a particular simulation software implementation. The difficulty of the former activity is largely irreducible, a conse quence of the inherent complexity of large, dynamic, and uncertain military systems such as airbase logistics. However, while the latter activity is also complex, key technologies have the potential to simplify this part of the modeling process. This paper discusses how a synergistic combination of object-oriented programming and data bases, graphical programming, software environments, and powerful computer worksta tions can provide significant enhancements to simulation modeling capabilities. In addition, the paper presents the object-oriented decomposi tion of the airbase logistics domain as it is implemented in IMDE. The paper also discusses how the IMDE design meets the needs of airbase logistics modelers with widely differing capabilities and mission requirements. This is accomplished by providing different modeling "levels", each with its own user interface, skill requirements and degree of access to modeling tools. The paper concludes with a description of the current status of this large scale research and development effort.

State of art and open issues on graphical user interfaces for object-oriented database systems

Graphical user interfaces have become very popular for database systems because they increase the usability of these applications. The functionality and ease-of-use of the graphical user interface, however, depend on the expressiveness and complexity of the underlying data model. With the advent of new database technology based on powerful data models like the object-oriented data model, new challenges and new opportunities are posed in user interface design. In the paper critical issues of graphical user interface development for object-oriented database systems are discussed.

Comparing Object‐Oriented and Relational Data Models for Project Control

This paper examines the objectoriented data base as an alternative to the traditional, pure relational data base for construction project control information. An entityrelationship ER model is deve...

Object-oriented query languages: the notion and the issues

The authors describe how the characteristics of an object-oriented data model, such as object identity, complex object structure, methods, and class hierarchies, have an impact on the design of a query language. They also point out major differences with respect to relational query languages. The discussion is supported through the definition of OOPC, a formal object-oriented query language based on predicate calculus, which incorporates in a consistent formal notation most features of existing object-oriented query languages. >

Optimization of object-oriented recursive queries using cost-controlled strategies

Object-oriented data models are being extended with recursion to gain expressive power. This complicates the optimization problem which has to deal with recursive queries on complex objects. Because unary operations invoking methods or path expressions on objects may be costly to execute, traditional heuristics for optimizing recursive queries are no longer valid. In this paper we propose a cost-based optimization method which handles object-oriented recursive queries. In particular, it is able to delay the decision of pushing selective operations through recursion until the effect of such a transformation can be measured by a cost model. The approach integrates rewriting and increases the optimization opportunities for recursive queries on objects while allowing for efficient optimization.

Designing and prototyping data-intensive applications in the Logres and Algres programming environment

The authors present an environment and a methodology for the design and rapid prototyping of data-intensive software applications, i.e., applications which perform substantial retrieval and update activity on persistent data. In the approach, the application is formally specified using Logres, a database language which combines object-oriented data modeling and rule-based programming. These specifications are translated into Algres, an extended relational algebra, thus yielding a rapid executable prototype. Algres programs embedded into a conventional programming language interface may be converted to conventional programs operating on a commercial relational system. This methodology helps automate the conversion from declarative requirements to imperative code, performing several tasks fully automatically and reducing the probability of human errors, while integrity constraints and application specifications are expressed in a declarative language, at a very high level of abstraction. >

Executive-centred system design for CAD applications

The paper discusses the development of a system architecture that is suitable for CAD applications. A generic structure is described that encompasses the interactions of the major components of the system. An object-oriented data structure and database-management system are also considered, and, finally, the application of the overall structure to a practical CAD problem is described with the software implementation details.

An object-oriented representation of structured process models

Efficient process modeling is a key requirement for widespread use of model-based techniques for process design and operation in an industrial environment. It can only be met by advanced knowledge based software tools to cut down the effort for model development and maintenance. A suitably designed model base providing generic modeling knowledge as well as a validated family of models of varying degree of detail for a certain process is one of the main components of such a modeling system. This contribution focuses on the design of the model base which is treated as a database design problem. Proper process model structuring, formalization of the modeling knowledge by means of an object-oriented data model, and some implementational issues are considered.

Structuring the Distributed Object World of CIM 1

This papers thesis is that today’s object-oriented data models do not offer enough expressiveness to structure the distributed world of CIM in an appropriate manner. Two relationships useful for modeling CIM applications which common object-oriented models lack are identified. The first expresses that some objects describe different prospectives — or facets — of one entity in the real world. The other represents the distribution of activities within a factory. The usefulness of both relationships is argued and a comparison with other relationships which are mentioned in the literature is given.

Raster GIS: Models of raster encoding

Abstract A fundamental problem for Geographical Information systems (GIS) is the need to interrelate spatial and nonspatial data into a system that can handle both spatially and object-oriented types of query. It is natural to structure the data primarily with respect either to the spatial or to the nonspatial information. The former selection leads to encodings of the raster type. There are potentially infinitely many addressing schemes for individual locations; any of these may be used as the basis for a simple raster encoding, a run-length encoding or (intermediate between these) an encoding analogous to the linear quadtree. The paper presents a unified view of such schemes, considers questions of storage and image-processing efficiency, and concludes with a brief look at the problem of integrating raster, vector, and object-oriented data types in GIS.

An Object-Relationship Diagrammatic Technique for Object-Oriented Database Definitions

An object-relationship diagrammatic technique for communicating object-oriented database definitions is proposed and analysed. The technique permits diagrammatic display of objects in terms of system generated object identifiers, simple attributes, collection attributes, and both simple and collection reference attributes. Object-relationship diagrams are meant for final database designs with the OO approach, and are not intended to replace the entityrelationship diagrams commonly used in the early stages of data base design. They are intended mainly for ease of communication of complex database structure - particularly the inherently complex relationship aspects of object-oriented data base structure - to programmers and others involved in using OO databases.

A self-organizing knowledge representation scheme for extensible heterogeneous information environment

The self-organizing knowledge representation aspects in heterogeneous information environments involving object-oriented databases, relational databases, and rulebases are investigated. The authors consider a facet of self-organizability which sustains the structural semantic integrity of an integrated schemea regardless of the dynamic nature of local schemata. To achieve this objective, they propose an overall scheme for schema translation and schema integration with an object-oriented data model as common data model, and it is shown that integrated schemata can be maintained effortlessly by propagating updates in local schemata to integrated schemata unambiguously.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Database research at IPSI

At the Integrated Publication and Information Systems Institute (IPSI) of the GMD (Gesellschaft für Mathematik und Datenverarbeitung) database research is focused towards distributed database management systems to support the integration of heterogeneous multi-media information bases needed in an integrated publishing environment. The objective is to investigate advanced object-oriented and active data modelling concepts together with the principles of distributed data stores and data management. The unifying basis for the database research is the object-oriented data model VML developed in the project VODAK over the last four years. The data model is based on recursively defined meta classes, classes and instance hierarchies paired with a strict separation of structural and operational definitions in a polymorphic type system. This report describes the highlights of the work on the VODAK database system, the research efforts in heterogeneous database integration and the research plans of the multimedia database project as well as applications of our system in different environments such as hypertext and office automation.

A FRAMEWORK FOR SUPPORTING TRIGGERS IN OBJECT-ORIENTED DATABASE SYSTEMS

An active database system reacts to a set of external events such as a timer interrupt or access to a particular object in the database. A trigger is a general mechanism for active data management, both in the context of a centralized system or a distributed system (including that of autonomous and cooperating agents). It consists of three parts; event specification, integrity constraint specification, and action specification. The event specification in a trigger is a set of events which will cause the condition in the constraint specification to be checked. If the condition is true, the actions in the action specification will be initiated. In this paper, we develop a framework for supporting triggers in object-oriented database systems. The framework consists of a categorization for each of the three components of a trigger. The framework is first cast in the context of the relational model of data, and is then extended to account for object-oriented concepts that constitute an object-oriented data model, including nested objects, methods, and inheritance hierarchy.