Stubborn sets for model checking the EF/AG fragment of CTL

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: Model-Checking with Coverability Graphs
abstract: We show that several formulas of a temporal logic can be verified using the coverability graph of the underlying system. Of course, the procedure is not capable of verifying all formulae, since already the reachability problem for (unbounded) Petri nets is computationally hard. Thus, the procedure returns true, false, or unknown for a query. The formulae that can be verified cover most of the well known standard properties which have been listed in the context of coverability graph analysis so far.

title: Distributed verification with LoLA
abstract: We report work in progress on a distributed version of explicit state space generation in the Petri net verification tool LoLA. We propose a data structure where all available memory of all involved workstations can be fully exploited, and load balancing actions are possible at any time while the verification is running. It is even possible to extend the set of involved workstations while a verification is running.

title: LoLA: a low level analyser
abstract: With LoLA, we put recently developed state space oriented algorithms to other tool developers disposal. Providing a simple interface was a major design goal such that it is as easy as possible to integrate LoLA into tools of different application domains. LoLA supports place/transition nets. Implemented verification techniques cover standard properties (liveness, reversibility, boundedness, reachability, dead transitions, deadlocks, home states) as well as satisfiability of state predicates and CTL model checking. For satisfiability, both exhaustive search and heuristically goal oriented system execution are supported. For state space reduction, LoLA features symmetries, stubborn sets, and coverability graphs.

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: The promise of solid state disks: increasing efficiency and reducing cost of DBMS processing
abstract: Most database systems (DBMSs) today are operating on servers equipped with magnetic disks. In our contribution, we want to motivate the use of two emerging and striking technologies, namely native XML DBMSs (XDBMSs for short) and solid state disks. In this context, the traditional read/write model optimized by a sophisticated cache hierarchy and the IO cost model for databases needs adjustment. Such new devices together with optimized storage mapping of XML documents provide a number of challenging characteristics. We discuss howtheir optimization potential ca be exploited to enhance transactional DB performance under reduced energy consumption to match increasing application demands and, at the same time, to guarantee economic energy use in data centers.

title: Autonomous Management of Soft Indexes
abstract: In recent years the support for index tuning as pan of physical database design has gained focus in research and product development, which resulted in index and design advisors. Nevertheless, these tools provide a one-off solution for a continuous task and are not deeply integrated with the DBMS functionality by only applying the query optimizer for index recommendation and profit estimation and decoupling the decision about and execution of index configuration changes from the core system functionality. In this paper we propose an approach that continuously collects statistics for recommended indexes and based on this, repetitively solves the Index Selection Problem (lSP).A key novelty is the on-the-fly index generation during query processing implemented by new query plan operators In-dexBuildScan and SwitchPlan. Finally, we present the implementation and evaluation of the introduced concepts as part of the PostgreSQL system.

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: Tailor-Made Native XML Storage Structures
abstract: Automatically choosing suitable native storage structures for XML doc- uments arriving at the XML DBMS is a challenging task for its storage manager. While some of the critical parameters require pre-specification, others can be deter- mined by pre-analysis or sampling of the incoming document or by just making ex- perience-driven "educated guesses". In this paper, we discuss approaches to achieve an adaptive behavior of the storage manager to provide tailor-made native XML stor- age structures to the extent possible. 1I ntroduction The XML data model allows for a great deal of modeling flexibility with which order, op- tional and multi-valued concepts, as well as deeply nested relationships can be captured. Therefore, the resulting tree structures of natively represented XML documents exhibit large variations in breadth and depth. Furthermore, XML documents may be data-centric having relatively little 'content' stored as short text values or they may be document-cen- tric where a single content node may contain huge portions of text, e.g., an entire book in a digital library. For these reasons, it is highly advisable to equip the storage manager with the ability to select reasonable or even optimal storage structures for documents. Furthermore, two cas- es have to be considered: a document sent by a client arrives at a time—the so-called block mode, i.e., the document can be pre-parsed and analyzed before a storage structure is cho- sen—or it arrives at the DBMS interface in stream mode where fragments present, due to their size, have to be allocated in a suitable storage structure on disk before the entire "streamed" document is available for the DBMS. In the latter case, the storage manager must decide—based on imprecise structural information—on the storage structure to be chosen and, at best, can make some educated guesses based on context or sampling infor- mation.

title: Fallstudie zur Modellierung von Software-Entwicklungsprozessen auf Basis von SPEM 2.0
abstract: The instant invention is directed to a method of producing a reaction mixture for forming solid or cellular materials from flowable reactants and, optionally, fillers, comprising premixing the components and, optionally, fillers in a first mixing zone and after-mixing in a second mixing zone, the improvement wherein said after-mixing is carried out in a slit-like annular zone which extends radially from the center, the surface boundaries of said annular zone are not parallel and one of said surface boundaries is rotated while the opposite facing surface boundary remains stationary. The instant invention is also directed to an apparatus for producing a reaction mixture for forming solid or cellular materials from flowable reactants and, optionally, fillers, comprising: (a) storage containers for reactants, from which (b) feed pipes lead via (c) metering pumps to a (d) premixing chamber which is arranged in a (e) housing, and on whose outlet opening an (f) after-mixing chamber is connected, the improvement wherein (g) said after-mixing chamber comprises a slit which is formed by (h) two baffle plates, one of which is provided with a (i) rotary drive.