Controllability of Open Workflow Nets.
An open workflow net is basically a workflow net extended with a message passing interface. Open workflow nets are adequate models for services or parts of inter-organizational business processes. We investigate the problem of controllability, a natural counterpart of soundness in classical workflow nets (as studied by van der Aalst). We distinguish centralized, distributed, and local controllability and provide solutions to all problems.

title: Verification of Siphons and Traps for Algebraic Petri Nets
abstract: Siphons and traps are structures which allow for some implications on the net's behaviour and can be used in manual correctness proofs for concurrent systems. We introduce symbolic representations of siphons and traps which work quite well even in infinite cases and are still intuitively readable. The verification of symbolic siphons and traps is traced back to unification and structural induction on the terms. This approach is motivated by some additional considerations. For unification and other proposed structural reasoning mechanisms tool support is given by completeness proof tools studied in the theorem-proving community.

title: Stubborn Sets for Standard Properties
abstract: Stubborn sets are a tool for state space reduction preserving certain system properties. We present stubborn set approaches for all popular Petri net standard properties. This extends the list of properties that can be analysed successfully (including boundedness, reversibility). For other properties, our approach can lead to larger reductions (reachability) than previous ones. Furthermore, shortest and chepest witness paths for several properties are now preserved.

title: LoLA wird Pfadfinder.
abstract: LoLA ist ein erreichbarkeitsgraphbasiertes Werkzeug f ur Stellen/Transitions{Netze. Hier geht es um LoLAs Fahigkeit, erreichbare Zustande mit vorgegebenen Eigenschaften zu suchen und im Erfolgsfall einen solchen Zustand mit einem Weg von der Anfangsmarkierung dorthin anzugeben. Die Besonderheit besteht darin, da wahrend der Suche nur zwei Zustande gespeichert werden: der Anfangszustand und der aktuelle Zustand. Anstatt also den Zustandsraum systematisch zu durchmustern (und dabei meist am Speicherende zu scheitern), navigiert LoLA ohne Kenntnis der schon betretenen Zustande durch den Erreichbarkeitsgraph. Da sie trotzdem ihre Aufgabe erfolgreich lost, liegt an ihren spezi schen Fahigkeiten: Schnelligkeit, Bescheidenheit, Zielstrebigkeit, Neugier und Ausdauer.

title: Narrowing Petri Net State Spaces Using the State Equation
abstract: Given a (possibly partially defined) state, all count vectors of transition sequences reaching that state are solutions to a corresponding Petri net state equation. We propose a search strategy where sequences corresponding to a minimal solution of the state equation are explored first. Then step by step the search space is relaxed to arbitrary count vectors. This heuristics relies on the observation that in many (though provably not in all) cases, minimal solutions of the state equation can be realized as a firing sequence. If no target state is reachable, either the state equation does not have solutions, or our search method would yield the full state space. We study the impact of the state equation on reachability, present an algorithm that exploits information from the state equation and discuss its application in stateless search as well as its combination with stubborn set reduction.

title: How to calculate symmetries of Petri nets
abstract: Symmetric net structure yields symmetric net behaviour. Thus, knowing the symmetries of a net, redundant calculations can be skipped. We present a framework for the calculation of symmetries for several net classes including place/transition nets, timed nets, stochastic nets, self–modifying nets, nets with inhibitor arcs, and many others. Our approach allows the specification of different symmetry groups. Additionally it provides facilities either to calculate symmetries on demand while running the actual analysis algorithm, or to calculate them in advance. For the latter case we define and calculate a ground set of symmetries. Such a set has polynomial size and is sufficient for an efficient implementation of the for all symmetries loop and the partition of net elements into equivalence classes. These two constructions are the usual way to integrate symmetries into an analysis algorithm.

title: An Adaptive Storage Manager for XML Documents
abstract: Effective and efficient management and manipulation of XML documents requires stable decisions at the time a document enters the XML DBMS to provide for storage structures which are adjusted to the document characteristics and which reflect the future processing needs. While some of the critical parameters require a kind of pre-specification, others can be determined by pre-analysis or sampling of the incoming document or by just making experience-driven “educated guesses”. Important parameters are related to node labeling, path synopsis, document container layout, and indexing. In this paper, we discuss approaches to achieve an adaptive behavior of the storage manager to provide tailor-made native XML storage structures to the extent possible.

title: Usage-driven storage structures for native XML databases
abstract: There are numerous and influential parameters associated with the selection of suitable native storage structures for XML documents within an XML DBMS. The most important parameters are related to node labeling, path synopsis, document container layout, indexing, and text compression. While node labeling and the presence of a path synopsis greatly determine flexibility and efficiency of the entire DBMS-internal XML processing, the remaining issues primarily address I/O demand and space consumption. In particular, text compression---considered orthogonal to the design choices affected by the other parameters---implies additional algorithmic costs for encoding/decoding during document processing. Having the vision in mind that future storage managers can autonomously figure out optimal choices for all of these parameters, we discuss how various storage options favor different usage patterns and how they can be specified beforehand to influence native XML storage options by the anticipated usages.

title: Comparison of Complete and Elementless Native Storage of XML Documents
abstract: Because XML documents tend to be very large, are accessed by declarative and navigational languages, and often are processed in a collaborative way using read/write transactions, their fine-grained storage and management in XML DBMSs is a must for which, in turn, a flexible and space-economic tree representation is mandatory. In this paper, we explore a variety of options to natively store, encode, and compress XML documents thereby preserving the full DBMS processing flexibility on the documents required by the various language models and usage characteristics. Important issues of our empirical study are related to node labeling, document container layout, indexing, as well as structure and content compression. Encoding and compression of XML documents with their complete structure leads to a space consumption of ~40% to ~60% compared to their plain representation, whereas structure virtualization (elementless storage) saves in the average more than 10%, in addition.

title: Green Computing - A Case for Data Caching and Flash Disks?
abstract: Green computing or energy saving when processing information is primarily considered a task of processor development. However, this position paper advocates that a holistic approach is necessary to reduce power consumption to a minimum. We discuss the potential of integrating NAND flash memory into DB-based architectures and its support by adjusted DBMS algorithms governing IO processing. The goal is to drastically improve energy efficiency while comparable performance as is disk-based systems is maintained.

title: Adaptive Resource Management in a Native XDBMS
abstract: A graphite reinforced glass composite is described comprising discontinuous graphite fibers in substantially planar orientation in a glass matrix with strength and fracture toughness greater than the unreinforced glass matrix. The resulting composite has superior strength, fluid impermeability, wear resistance, failure strain and fracture toughness. In fact, the stress-strain, curve for composites of the invention resembles that of metal making it particularly suitable for a variety of moldable shapes and machinable designs.