UIB-2003-01 A Formal Framework for Workflow Type and Instance Changes Under Correctness Constraints.

Autoren: Manfred Reichert, Stefanie Rinderle, Peter Dadam

The capability to rapidly adapt in-progress workflows (WF) is an essential requirement for any workflow system. Adaptations may concern single WF instances or a WF type as a whole. While changes of single instances often have to be applied in an ad-hoc manner, type changes become necessary to adapt to evolving business processes. Especially for long-running processes it is indispensable to propagate type changes to running instances as well. Very challenging in this context is to correctly adapt a (potentially large) collection of WF instances, which may be in different states and to which various ad-hoc changes may have been previously applied. This paper presents a comprehensive framework for the support of both, WF type and WF instance changes. We establish general correctness principles and show how WF instances can be automatically and efficiently migrated to a modified WF schema. We point out that our approach exceeds existing adaptation models in formal foundation, completeness, and usability.

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UIB-2003-02 Supporting Workflow Schema Evolution By Efficient Compliance Checks

Autoren: Stefanie Rinderle, Manfred Reichert, Peter Dadam

Process-oriented support of collaborative work is an important challenge today. At first glance, Workflow Management Systems (WfMS) seem to be very suitable tools for realizing team-work processes. However, such processes have to be frequently adapted, e.g., due to process optimizations or when process goals change. Unfortunately, runtime adaptability still seems to be an unsolvable problem for almost all existing WfMS. Usually, process changes can be accomplished by modifying a corresponding (graphical) workflow (WF) schema. Especially for long-running processes, however, it is extremely important that such changes can be propagated to already running WF instances as well, but without causing inconsistencies and errors. In addition, team work often requires ad-hoc process modifications, i.e., individual changes of single WF instances. The paper presents a general and comprehensive correctness criterion for ensuring compliance of in-progress WF instances with a modified WF schema. For different kinds of WF schema changes, it is precisely stated, which rules and which information are needed at mininum for satisfying this criterion.

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UIB-2003-03 Safely Extending Procedure Types to Allow Nested Procedures as Values

Autoren: Christian Heinlein

The concept of nested procedure values, i. e., the possibility of using nested procedures as values of procedure types, is a useful and powerful concept. Nevertheless, it is not allowed in languages such as Modula-2 and Oberon(-2), because it creates a serious security hole when used inappropriately. To prevent such misuse while at the same time retaining the benefits of the concept, alternative language rules as well as a small language extension for Oberon-2 are suggested, which allow nested procedures to be safely used as values of procedure types and especially to pass them as parameters to other procedures.

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UIB-2003-04 On Dealing With Semantically Conflicting Business Process Changes

Autoren: Stefanie Rinderle, Manfred Reichert, Peter Dadam

Correct propagation of process type changes to long-running process instances and the capability to perform ad-hoc-modifications of individual process instances are essential requirements for any process management software.In particular, in many cases it becomes necessary to propagate process type changes to individually modified process instances as well. In doing so, one must not only enable state-related compliance checks, but is additionally confronted with structural and semantical conflicts that may exist between process type and process instance changes. For the first time, this paper identifies and classifies semantical conflicts between process type and instance changes, and illustrates them by sophisticated examples. In order to be able to adequately deal with semantical conflicts at change propagation time we provide formal methods for conflict detection and discuss strategies to deal with different kinds of semantically conflicting changes.

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UIB-2003-05 Dynamic Class Methods in Java

Autoren: Christian Heinlein

The concept of dynamic class methods in Java, constituting a specialization of a general new programming language concept called dynamic routines,is introduced and applied to a simple case study.Its advantages over standard object-oriented programming techniques including design patterns are demonstrated. Furthermore,an implementation of dynamic class methods as a precompiler-based language extension to Java is described.

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UIB-2003-06 Vertical, Horizontal, and Behavioural Extensibility of Software Systems

Autoren: Christian Heinlein

By distinguishing three different dimensions of extensibility -- vertical (extensions of the type hierarchy),horizontal (extensions of the spectrum of operations available on types),and behavioural (extensions or even modifications of the original behaviour of operations) --,it is shown that typical object-oriented programming languages support only the first dimension in a direct and modular way. On the other hand,a new and surprisingly simple concept called dynamic routines,that is introduced in this paper,simultaneously supports all three dimensions in a natural and flexible way. The concept has been implemented as precompiler-based language extensions for C++, Oberon-2, and Java.

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UIB-2003-07 Safely Extending Procedure Types to Allow Nested Procedures as Values (Corrected Version)

Autoren: Christian Heinlein

The concept of nested procedure values,i. e., the possibility of using nested procedures as values of procedure types,is a useful and powerful concept. Nevertheless,it is not allowed in languages such as Modula-2 and Oberon(-2), because it creates a serious security hole when used inappropriately.To prevent such misuse while at the same time retaining the benefits of the concept, alternative language rules as well as a small language extension for Oberon-2 are suggested,which allow nested procedures to be safely used as values of procedure types and especially to pass them as parameters to other procedures.

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UIB-2003-08 Survey of Mobile Ad Hoc Network Routing Protocols

Autoren: Changling Liu, Jörg Kaiser

Emerging ubiquitous computing needs "anytime and anywhere" network connections. Mobile ad hoc networks are well suited for this application area because they are self-organizing networks without depending on any network infrastructure. Due to the improved flexibility and reduced cost of mobile ad hoc networks, they promise to play an important role in future mobile applications. An important and essential issue for mobile ad hoc networks is routing protocol design. Because of the dynamic network features, it is a major technical challenge. During the last years, active research work resulted in a variety of proposals. A large number of protocols, each with a particular property and often optimized for a specific application area, have been designed. They follow different design principles and exhibit substantial variations in performance depending on network size or node mobility patterns. This report presents a state-of-the-art review and a comparison for typical representatives of routing protocols designed for mobile ad hoc networks. The report aims at providing criteria according to which the plethora of protocols can be classified. Because it is difficult to compare all protocols along the same criteria, which some protocols may have others not, we first identify major protocol classes and then provide an in depth comparison of related protocols of the same category.

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