117881226
Narrowing Petri Net State Spaces Using the State Equation
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.
60532280
Distributed verification with LoLA
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.
118762514
Stubborn Sets for Standard Properties
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.
172504304
LoLA wird Pfadfinder.
LoLA ist ein erreichbarkeitsgraphbasiertes Werkzeug f ur Stellen/Transitions{Netze. Hier geht es um LoLAs Fahigkeit, erreichbare Zustande mit vorgegebenen Eigenschaften zu suchen und im Erfolgsfall einen solchen Zustand mit einem Weg von der Anfangsmarkierung dorthin anzugeben. Die Besonderheit besteht darin, da wahrend der Suche nur zwei Zustande 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 Zustande durch den Erreichbarkeitsgraph. Da sie trotzdem ihre Aufgabe erfolgreich lost, liegt an ihren spezi schen Fahigkeiten: Schnelligkeit, Bescheidenheit, Zielstrebigkeit, Neugier und Ausdauer.
119954332
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.
118703657
Verification of Siphons and Traps for Algebraic Petri Nets
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.
14265278
An Adaptive Storage Manager for XML Documents
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.
42183436
Adaptive Resource Management in a Native XDBMS
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.
2745798
Autonomous Management of Soft Indexes
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.
10045308
Green Computing - A Case for Data Caching and Flash Disks?
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.
17363995

 Storing and indexing XML documents upside down

AbstractXML documents contain substantial redundancy in their structure part, because each path from the root
 node to a leaf node is explicitly represented and typically large sets of such path instances belong to
 a path class, i.e., the nodes of the path instances are labeled by the same sequence of element (or attribute)
 names. To save storage space and I/O cost, we want to get rid of this structural redundancy to the extent
 possible. While all known methods for the physical representation (storage) of XML documents proceed from
 the root via the element/attribute hierarchy (internal nodes) down to the leaves (values), we follow an
 upside-down approach which explicitly stores the values and only reconstructs
 the internal nodes, if needed. The cornerstones for such a solution are suitable node labels and a path
 synopsis which efficiently represents all path classes of an XML document. As a solution, we propose a compact
 internal storage format for native XML database systems where the inner structure of the stored documents
 is virtualized. Because this elementless storage format provides an efficient reconstruction of a document
 using its path synopsis, all processing properties are preserved and the semantics of navigational and declarative
 operations of XML languages remains unchanged. Adjusted indexes support the full spectrum of so-called
 content-and-structure single path queries. Apart from greatly reduced storage consumption, our approach
 demonstrates its superiority, compared to competing methods, not only for a substantial fraction of those
 queries, but also for storing, reconstructing, and navigating XML documents.
