Walter Liebhart

The Workflow Management System Panta Rhei

We present the prototypical workflow management system Panta Rhei which was designed to support various types of workflows in an uniform and elegant way. The main characteristics of this system are its flexibility, the lean architecture, the integration in the Web, the transactional features and its support of process management. We discuss the basic concepts of the system, its architecture and its implementation.

Optimization of Object-Oriented Queries by Inverse Methods

For object-oriented databases we propose a new technique for optimizing queries containing method invocations. This technique is based on the definition of inverse methods and query rewriting. It can be viewed as providing computed inverted access structures like (secondary) indexes provide stored inverted access structures. This technique can be applied to methods which can be fully specified as functions and to the usual comparison operations in queries. We introduce an extension to ODMG-93 [1] to define inverse methods and present the optimization algorithm for homogeneous as well as for heterogeneous collections. The application of this technique can reduce the cost of query-evaluation by orders of magnitude.