Thomas Kudrass

Rules in an Open System: The REACH Rule System

REACH is an active object system intended to control heterogeneous systems, possibly under timing constraints. When dealing with open systems in which the controlled system may execute irreversible actions, many notions of active databases must be revised and adapted to this situation. In this paper we draw the system boundaries between controlling and controlled system, present a rule system that includes events and actions both in the controlled and the controlling systems and analyze the effects of this open environment on the rule structure. We identify two new coupling modes, sequential causally dependent and exclusive causally dependent, which are necessary for handling irreversible actions in external systems and contingency plans, respectively.

Management of XML documents without schema in relational database systems

Abstract Many applications deal with highly flexible XML documents from different sources, which makes it difficult to define their structure by a fixed schema or a DTD. Therefore, it is necessary to explore ways to cope with such XML documents. The paper analyzes different storage and retrieval methods for schemaless XML documents using the capabilities of relational systems. We compare our experiences with the implementation of an XML-to-relational mapping with an LOB implementation in a commercial RDBMS. The paper concludes with a vision of how different storage methods could converge towards a common high-level XML-API for databases.

Rule-Based Generation of XML DTDs from UML Class Diagrams

We present an approach of how to extract automatically an XML document structure from a conceptual data model that describes the content of a document. We use UML class diagrams as the conceptual model that can be represented in XML syntax (XMI). The algorithm we present in the paper is implemented as a set of rules that transform the UML class diagram into an adequate document type definition (DTD). The generation of the DTD from the semantic model corresponds with the logical XML database design with the DTD as the database schema description. Therefore, we consider many semantic issues, such as the dealing with relationships, how to express them in a DTD in order to minimize the loss of semantics. Since our algorithm is based on XSLT stylesheets, its transformation rules can be modified in a very flexible manner in order to consider different mapping strategies and requirements.

Active object-relational mediators

The paper describes an active abject-oriented mediator for the enforcement of global consistency between relational legacy databases. The authors discuss the problem of integrating several local relational systems into a federated system by the usage of an object-oriented mediator system. They explore how relational DBMSs can be enhanced to signal local updates that may violate global constraints without sacrificing too much autonomy and present a database gateway for detection, logging and signalling. They show how the gateway is embedded into the architecture of an object-relational mediator system. They give a solution to the problem of mapping SQL commands to method calls in a C++ based system using a so-called mediator generator. Furthermore, they discuss how the federated system can be enriched by rule mechanisms that make the mediator behave actively.

Tool-Based Re-Engineering of a Legacy MIS: An Experience Report

In the process of restructuring its computing facilities, Rhone-Poulenc Rorer is eliminating its mainframes. As a consequence, existing legacy systems must be migrated. We present an experience report on the use of CASE tools for re-engineering a legacy MIS and illustrate the process of current state analysis and generation of a re-engineered target system. Based on the experience gained in evaluating representative CASE tools for their suitability in the data re-engineering process and the actual use of the ISEE tool we present a list of needed features missing from todays tools.

Management of XML Documents in Object-Relational Databases

Many applications deal with complex XML documents that need to be made persistent. We investigate the use of the object-relational modeling approach that combines both the strengths of object oriented concepts and relational DBMS technology provided by current DBMS vendors. As a prerequisite, we analyze the document definition and generate the equivalent object-relational database schema in SQL. We discuss the main issues when mapping XML documents to an object-relational target schema with the example of Oracle. The paper concludes with a summary of our experiences with the object-relational approach for XML document mangement.

Interdatabase existence dependencies: a metaclass approach

We present a novel approach to deal with the modeling and operational aspects of the interdatabase existence dependency problem. By extending our canonical model BLOOM with high level abstractions (metaclasses) for the different kinds of existence dependencies and their corresponding enforcement policies, inter-dependencies are declaratively specified and their behavior embodied into the model by exploiting the metaclass mechanism of BLOOM.<<ETX>>