issue for XML research and development. However, how to view XML documents determines how they can be queried. In this paper, we first describe a natural way to view XML documents as in complex object data models so that we can easily comprehend XML data from database point of view. We then illustrate how to use logical variables to extract data from XML documents. We also describe a rule-based declarative query language for XML. We demonstrate that our rule-based language provides a uniform framework that is advantageous over other XML query languages including XQuery in the following ways. First, it provides a natural way for separating querying and result constructing using the body and the head respectively. Second, several rules can be used for the same query so that complex queries can be expressed in a simple and natural way. Also, its use of logical variables and rules makes many functions and operators in XQuery and XPath unnecessary or definable constructively. Finally, it provides a natural and direct support for recursion as in deductive databases and has logical foundations that have played a significant role in database research in the past.

This article takes us another step towards solving this problem. Two features that are currently missing are the encapsulation of rule-based methods in classes, and nonmonotonic structural and behavioral inheritance with overriding, conflict resolution and blocking. This article introduces the syntax of a language with these features. The language is restricted in the sense that we have omitted other object-oriented and deductive features that are now well understood, in order to make our contribution clearer. It then defines a class of databases, called well-defined databases, that have an intuitive meaning and develops a direct logical semantics for this class of databases. The semantics is based on the well-founded semantics from logic programming. The work presented in this article establishes a firm logical foundation for deductive object-oriented databases

The semantics of static deductive databases is well understood based on the work in logic programming. In the past decade, various methods to incorporate update constructs into logic programming and deductive databases have been proposed. However, there is still no consensus about the appropriate treatment of dynamic behavior in deductive databases. In this paper, we propose a language called DatalogU, which is a minimal but powerful extension of Datalog with updates to base relations. DatalogU allows the user to program set-oriented complex database transactions with concurrent, disjunctive and sequential update operations in a simple and direct way. It has a simple and intuitive declarative semantics that naturally accounts for set-oriented updates in deductive databases.

Logic programming, object-oriented programming and soft computing have provided advantageous methodologies and techniques for computer-based problem solving. This paper proposes a framework that combines these three disciplines to exploit their own advantages in dealing with real world problems. The framework is a logic-based one in which class and object properties are represented by clauses. Vague data in properties are represented by fuzzy sets interpreted as possibility distributions. Uncertain applicability of a property to a class or an object is represented either by a support pair defining probability lower and upper bounds, or by a certainty lower bound. Fundamental issues of uncertain membership and inheritance are then discussed and solutions to them are proposed. The result forms a basis for development of soft computing object-oriented programming systems. 1. Introduction For dealing with real world problems, which are too complicated to be solved by a single methodology...

) Mengchi Liu Department of Computer Science, University of Regina Regina, Saskatchewan, Canada S4S 0A2 mliu@cs.uregina.ca http://www.cs.uregina.ca/mliu Abstract. Deductive object-oriented databases are intended to combine the best of the deductive and object-oriented approaches. However, some important object-oriented features are not properly supported in the existing proposals. This paper proposes a novel deductive language that supports important structurally object-oriented features such as object identity, complex objects, typing, classes, class hierarchies, multiple property inheritance with overriding, conict-handling, and blocking, and schema denitions in a uniform framework. The language eectively integrates useful features in deductive and object-oriented database languages. The main novel feature is the logical semantics that cleanly accounts for those structurally object-oriented features that are missing in object-oriented database languages. Therefor...