Michael Gillmann

XML-enabled workflow management for e-services across heterogeneous platforms

Abstract. Advanced e-services require efficient, flexible, and easy-to-use workflow technology that integrates well with mainstream Internet technologies such as XML and Web servers. This paper discusses an XML-enabled architecture for distributed workflow management that is implemented in the latest version of our Mentor-lite prototype system. The key asset of this architecture is an XML mediator that handles the exchange of business and flow control data between workflow and business-object servers on the one hand and client activities on the other via XML messages over http. Our implementation of the mediator has made use of Oracles XSQL servlet. The major benefit of the advocated architecture is that it provides seamless integration of client applications into e-service workflows with scalable efficiency and very little explicit coding, in contrast to an earlier, Java-based, version of our Mentor-lite prototype that required much more code and exhibited potential performance problems.

Integrating light-weight workflow management systems within existing business environments

Workflow management systems (WfMSs) support the efficient, largely automated execution of business processes. However, using a WfMS typically requires implementing the applications control flow exclusively by the WfMS. This approach is powerful if the control flow is specified and implemented from scratch, but it has severe drawbacks if a WfMS is to be integrated within environments with existing solutions for implementing control flow. Usually, the existing solutions are too complex to be substituted by the WfMS all at once. Hence, the WfMS must support an incremental integration, i.e. the reuse of existing implementations of control flow as well as their incremental substitution. Extending the WfMSs functionality according to future application needs, e.g. by worklist and history management, must also be possible. In particular, at the beginning of an incremental integration process, only a limited amount of a WfMSs functionality is actually exploited by the workflow application. Later on, as the integration proceeds, more advanced requirements arise and demand the customization of the WfMS to the evolving application needs. In this paper, we present the architecture and implementation of a light-weight WfMS, coined Mentor-lite, which aims to overcome the above-mentioned shortcomings of conventional WfMSs. Mentor-lite supports an easy integration of workflow functionality into an existing environment, and can be tailored to specific workflow application needs.

Benchmarking and Configuration of Workflow Management Systems

Workflow management systems (WFMS) are a cornerstone of mission-criticial, possibly cross-organizational business processes. For large-scale applications both their performance and availability are crucial factors, and the system needs to be properly configured to meet the application demands. Despite ample work on scalable system architectures for workflow management, the literature has neglected the important issues of how to systematically measure the performance of a given system configuration and how to determine viable configurations without resorting to expensive trial-and-error or guesswork. This paper proposes a synthetic benchmark for workflow management systems; based on the TPC-C order-entry benchmark, a complete e-commerce workflow is specified in a system-independent form. This workflow benchmark, which stresses all major components of a workflow system and is parameterized in a flexible manner, has been applied to two operational systems, the commercial system Staffware97 and our own prototype system Mentor-lite. The paper reports performance results from our measurements and discusses lessons learned. In particular, the results demonstrate the scalability of the Mentor-lite architecture. The measurements also underline the need for configuring systems intelligently, and the paper outlines an auto-configuration tool that we have been building to this end.

A goal-driven auto-configuration tool for the distributed workflow management system mentorlite

The Mentor-lite prototype has been developed within the research project “Architecture, Configuration, and Administration of Large Workflow Management Systems” funded by the German Science Foundation (DFG). It has evolved from its predecessor Mentor [1], but aims at a simpler architecture. The main goal of Mentor-lite has been to build a light-weight, extensible, and tailorable workflow management system (WFMS) with small footprint and easy-to-use administration capabilities. Our approach is to provide only kernel functionality inside the workflow engine, and consider system components like history management and worklist management as extensions on top of the kernel. The key point to retain the light-weight nature is that these extensions are implemented as workflows themselves. The workflow specifications are interpreted at runtime, which is a crucial prerequisite for flexible exception handling and dynamic modifications during runtime. The interpreter performs a stepwise execution of the workflow specification according to its formal semantics. For each step, the activities to be performed by the step are determined and started. Mentor-lite supports a protocol for distributed execution of workflows spread across multiple workflow engines. This support is crucial for workflows that span large, decentralized enterprises with largely autonomous organizational units or even cross multiple enterprises to form so-called “virtual enterprises”. A communication manager is responsible for sending and receiving synchronization messages between the engines. In order to guarantee a consistent global state even in the presence of site or network failures, we have built reliable message queues using the CORBA Object Transaction Services. For administration, Mentor-lite provides a Java-based workbench for workflow design, workflow partitioning across multiple workflow servers, and a Java-based runtime monitoring tool.

Tape-disk join strategies under disk contention

Large-scale data warehousing, data mining and scientific applications require the analysis of terabytes of factual data accumulated over long periods of time. Tape libraries are suitable for storing such mass data. The online analytical processing (OLAP) of this data typically leads to long-running aggregation queries joining the tape-resident fact relations with disk-resident dimension relations. During the join execution, the disks storing the dimension relations are often not dedicated to the join. They are subject to reads and writes invoked by concurrently running applications. In many cases, the performance of these concurrent applications should not be degraded too much by the processing of the join. We present an accurate model for analysing the performance of three different tape-disk join strategies in multi-query systems. The major contributions are: (a) a cost model considering tape and disk bandwidth, tape and disk latencies, available buffer sizes, CPU costs and the selectivity of filters on tape data; (b) disk queueing effects due to concurrent reads and writes at the disk; and (c) two disk scheduling strategies. We show the superiority of a disk scheduling strategy that gives preference to the servicing of the concurrent disk load. We present a strategy for dynamically selecting the most beneficial join algorithm and its parameters at run time. We have implemented the join strategies in a prototype system based on detailed simulations of secondary and tertiary storage devices. Our evaluations confirm that the model is very accurate and a suitable basis for run-time strategy decisions.

Benchmarking von Workflow-Management-Systemen (Kurzbeitrag)

Heute verfugbare Workflow-Management-Systeme (WfMS) weisen in ihrer Leistungsfahigkeit und Skalierbarkeit deutliche Defizite auf. Wahrend an Verbesserungen intensiv gearbeitet wird, sollten Leistungsvergleiche zwischen verschiedenen WfMS generell auf eine systematische, objektive Basis gestellt werden. Zu diesem Zweck entwickelt dieser Kurzbeitrag einen Benchmark fur WfMS, der — ausgehend von den Basisaktivitaten des TPC-C-Benchmarks — in verschiedenen Ausbaustufen Starken und Schwachen von WfMS ausloten und systematisch vergleichen kann. Die Benchmark-Definition wagt sorgfaltig ab zwischen Einfachheit, Realitatsnahe und Aussagekraft von Benchmark-Messungen und ist in dem im Industriestandard UML verwendeten State- und Activity-Chart-Formalismus spezifiziert.