Performance Evaluation for Clustering Algorithms in Object-Oriented Database Systems

International audienceIt is widely acknowledged that good object clustering is critical to the performance of object-oriented databases. However, object clustering always involves some kind of overhead for the system. The aim of this paper is to propose a modelling methodology in order to evaluate the performances of different clustering policies. This methodology has been used to compare the performances of three clustering algorithms found in the literature (Cactis, CK and ORION) that we considered representative of the current research in the field of object clustering. The actual performance evaluation was performed using simulation. Simulation experiments we performed showed that the Cactis algorithm is better than the ORION algorithm and that the CK algorithm totally outperforms both other algorithms in terms of response time and clustering overhead

Object-oriented data modeling

The object-oriented paradigm models local behavior, and to a lesser extent, the structure of a problem. Semantic data models describe structure and semantics. This thesis unifies the behavioral focus of the object-oriented paradigm with the structural and semantic focus of semantic data models. The approach contains expressive abstractions to model static and derived data, semantics, and behavior. The abstractions keep the data model closer to the problem domain, and can be translated into a relational (or other) implementation. The paper makes six contributions. First, a comprehensive set of data structuring abstractions are described. Second, the abstractions are compared to the entity-relationship and relational models. Third, semantic information inherent in the functional representation of the abstractions is identified. Fourth, a set of behavioral abstractions are described. Fifth, an algorithm that describes the dynamics between mathematically derived attributes of cooperating objects is presented. Sixth, weaknesses of object-oriented programming languages are identified

Grand tour of concepts for object-orientation from a database point of view

Over the last few years, object-orientation has gained more and more importance within several disciplines of computer science (e.g. programming languages, knowledge engineering, and database systems). Numerous papers have defined one or another of its underlying concepts (sometimes in quite different ways), and some systems have been developed following those heterogeneous definitions. Nevertheless, papers investigating the dependencies and degrees of freedom of these concepts are rarely found. For this reason, the goal of this paper is not to add yet another definition of object-oriented concepts, but to identify existing relationships among these basic concepts that allow one to cover and classify various conceivable combinations of these conceptual building blocks. Dependencies, orthogonalities, and relations among concepts like object identity, encapsulation, classification, generalization, inheritance, etc. are revealed, showing numerous ways to compose different shades of object-orientation. This leads to alternatives encountered when constructing object-oriented systems, which are illustrated by classifying some well-known systems and prototypes from different areas. However, it is not our purpose to analyze the relative importance of these concepts. Instead, we investigate the concepts from a neutral point of view, presenting (but not evaluating) several degrees of object-orientation

Function-based indexing for object-oriented databases

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 167-171).by Deborah Jing-Hwa Hwang.Ph.D

Incremental Attribute Evaluation for Multi-User Semantics-Based Editors

This thesis addresses two fundamental problems associated with performing incremental attribute evaluation in multi-user editors based on the attribute grammar formalism: (1) multiple asynchronous modifications of the attributed derivation tree, and (2) segmentation of the tree into separate modular units. Solutions to these problems make it possible to construct semantics-based editors for use by teams of programmers developing or maintaining large software systems. Multi-user semantics based editors improve software productivity by reducing communication costs and snafus. The objectives of an incremental attribute evaluation algorithm for multiple asynchronous changes are that (a) all attributes of the derivation tree have correct values when evaluation terminates, and (b) the cost of evaluating attributes necessary to reestablish a correctly attributed derivation tree is minimized. We present a family of algorithms that differ in how they balance the tradeoff between algorithm efficiency and expressiveness of the attribute grammar. This is important because multi-user editors seem a practical basis for many areas of computer-supported cooperative work, not just programming. Different application areas may have distinct definitions of efficiency, and may impose different requirements on the expressiveness of the attribute grammar. The characteristics of the application domain can then be used to select the most efficient strategy for each particular editor. To address the second problem, we define an extension of classical attribute grammars that allows the specification of interface consistency checking for programs composed of many modules. Classical attribute grammars can specify the static semantics of monolithic programs or modules, but not inter-module semantics; the latter was done in the past using ad hoc techniques. Extended attribute grammars support programming-in-the-large constructs found in real programming languages, including textual inclusion, multiple kinds of modular units and nested modular units. We discuss attribute evaluation in the context of programming-in-the-large, particularly the separation of concerns between the local evaluator for each modular unit and the global evaluator that propagates attribute flows across module boundaries. The result is a uniform approach to formal specification of both intra-module and inter-module static semantic properties, with the ability to use attribute evaluation algorithms to carry out a complete static semantic analysis of a multi-module program

Univers: The construction of an internet-wide descriptive naming system

Descriptive naming systems allow clients to identify a set of objects by description. Described here is the construction of a descriptive naming system, called Univers, based on a model in which clients provide both an object description and some meta-information. The meta-information describes beliefs about the query and the naming system. Specifically, it is an ordering on a set of perfect world approximations, and it describes the preferred methods for accommodating imperfect information. The description is then resolved in a way that respects the preferred approximations

A transputer based parallel database system.

A sophisticated database application generation environment known as DB4GL has been developed at Sheffield City Polytechnic. A unique feature of DB4GL is the object-oriented application model used to specify and generate database applications. Although DB4GL has many advanced and powerful features, such as a self-describing data dictionary and extensive integrity rule processing facilities; the system has not been designed for high performance in either the generation tools or the generated database applications. The Parallel-DB4GL (P-DB4GL) project represents an attempt to improve the performance of the generated database applications, by constructing a new concurrent implementation of DB4GL for execution on transputer-based parallel hardware. This thesis describes the DB4GL system as developed to the commencement of the P-DB4GL project. A prototype P-DB4GL system has been implemented that demonstrates how significant performance gains can be obtained from a concurrent implementation on transputer-based parallel hardware. Based on the successful results of this prototype system, designs for a fully functional multiprocessor P-DB4GL system are proposed. The details of this prototype and the fully functional designs are presented in this thesis. The thesis also provides an evaluation of the P-DB4GL project as a whole, and concludes with some suggestions for further research in the areas of parallel databases and object-oriented system implementation

Information resources management, 1984-1989: A bibliography with indexes

This bibliography contains 768 annotated references to reports and journal articles entered into the NASA scientific and technical information database 1984 to 1989