Jan Friso Groote

Structured operational semantics and bisimulation as a congruence

In this paper the question is considered in which cases a transition system specification in Plotkin style has ‘good’ properties and deserves the predicate ‘structured’. The discussion takes place in a setting of labelled transition systems. The states of the transition systems are terms generated by a single sorted signature and the transitions between states are defined by conditional rules. We argue that in this setting it is natural to require that strong bisimulation equivalence is a congruence on the states of the transition systems. A general format, called the tyft/tyxt format, is presented for the conditional rules in a transition system specification, such that bisimulation is always a congruence when all the rules fit into this format. With a series of examples it is demonstrated that the tyft/tyxt format cannot be generalized in any obvious way. Briefly we touch upon the issue of modularity of transition system specifications. We show that certain pathological tyft/tyxt rules (the ones which are not pure) can be disqualified because they behave badly with respect to modularisation. Next we address the issue of full abstraction. We characterize the completed trace congruence induced by the operators in pure tyft/tyxt format as 2-nested simulation equivalence. The pure tyft/tyxt format includes the format given by De Simone [16, 17] but is incomparable to the GSOS format of Bloom, Istrail & Meyer [7]. However, it turns out that 2-nested simulation equivalence strictly refines the completed trace congruence induced by the GSOS format.

The Syntax and Semantics of μCRL

A simple specification language based on CRL (Common Representation Language)and therefore called μCRL (micro CRL) is proposed. It has been developed to study processes with data. So the language contains only basic constructs with an easy semantics. To obtain executability, effective μCRL has been defined. In effective μCRL equivalence between closed data-terms is decidable and the operational behaviour is finitely branching and computable. This makes effective μCRL a good platform for tooling activities.

Parallel and Distributed Processing and Applications

Keynote Speech.- Self-stabilizing Distributed Algorithms for Networks.- Feature Extraction and Coverage Problems in Distributed Sensor Networks.- Peer-to-Peer Computing: From Applications to Platform.- Algorithms and Applications.- A Self-stabilizing Algorithm For 3-Edge-Connectivity.- Number of Processors with Partitioning Strategy and EDF-Schedulability Test: Upper and Lower Bounds with Comparison.- Architecture-Based Optimization for Mapping Scientific Applications to Imagine.- Implementation and Optimization of Sparse Matrix-Vector Multiplication on Imagine Stream Processor.- A Mutual Exclusion Algorithm for Mobile Agents-Based Applications.- A Distributed Metaheuristic for Solving a Real-World Scheduling-Routing-Loading Problem.- Cellular ANTomata.- Key-Attributes Based Optimistic Data Consistency Maintenance Method.- Parallelization Strategies for the Points of Interests Algorithm on the Cell Processor.- RWA Algorithm for Scheduled Lightpath Demands in WDM Networks.- Optimizing Distributed Data Access in Grid Environments by Using Artificial Intelligence Techniques.- Techniques for Designing Efficient Parallel Graph Algorithms for SMPs and Multicore Processors.- Distributed Memorization for the k -Vertex Cover Problem.- MADARP: A Distributed Agent-Based System for On-Line DARP.- An Incremental Distributed Algorithm for a Partial Grundy Coloring of Graphs.- Efficient Multidimensional Data Redistribution for Resizable Parallel Computations.- Distributed Local 2-Connectivity Test of Graphs and Applications.- Architectures and Systems.- Comparing Direct-to-Cache Transfer Policies to TCP/IP and M-VIA During Receive Operations in MPI Environments.- Virtual Distro Dispatcher: A Costless Distributed Virtual Environment from Trashware.- A Parallel Infrastructure on Dynamic EPIC SMT and Its Speculation Optimization.- An SRP Target Mode to Improve Read Performance of SRP-Based IB-SANs.- An FPGA Design to Achieve Fast and Accurate Results for Molecular Dynamics Simulations.- Performance and Complexity Analysis of Credit-Based End-to-End Flow Control in Network-on-Chip.- An QoS Aware Mapping of Cores Onto NoC Architectures.- Latency Optimization for NoC Design of H.264 Decoder Based on Self-similar Traffic Modeling.- Hardware Implementation of Common Protocol Interface for a Network-Based Multiprocessor.- Datamining and Databases.- A Distributed Hebb Neural Network for Network Anomaly Detection.- Processing Global XQuery Queries Based on Static Query Decomposition.- Formal Verification and Performance Evaluation of User Query Pattern-Based Relational Schema-to-XML Schema Translation Algorithm.- Adaptive Processing for Continuous Query over Data Stream.- Parallel Computation of Closed Itemsets and Implication Rule Bases.- An Optimal Share Transfer Problem on Secret Sharing Storage Systems.- Deadline and Throughput-Aware Control for Request Processing Systems.- Cluster Recovery for Fault Tolerance of Spatial Database Cluster in Sensor Networks.- Fault Tolerance and Security.- A Secure Energy-Efficient Routing Protocol for WSN.- Designing Scalable Self-healing Key Distribution Schemes with Revocation Capability.- Key Predistribution Using Partially Balanced Designs in Wireless Sensor Networks.- An Efficient ID-Based Authenticated Key Agreement Protocol with Pairings.- Leveraging Many Simple Statistical Models to Adaptively Monitor Software Systems.- Binomial Graph: A Scalable and Fault-Tolerant Logical Network Topology.- Eventually Perfect Failure Detectors Using ADD Channels.- Stochastic Communication Delay Analysis of Adaptive Wormhole-Switched Routings in Tori with Faults.- An Efficient Fault-Tolerant Routing Methodology for Fat-Tree Interconnection Networks.- On the Optimality of Rollback-Recovery Protocol Preserving Session Guarantees.- Middleware and Cooperative Computing.- A Replication Software Architecture(RSA) for Supporting Irregular Applications on Wide-Area Distributed Computing Environments.- Cooperative Grid Jobs Scheduling with Multi-objective Genetic Algorithm.- A Pro-middleware for Grids Computing.- On Formal MOM Modeling.- Performability Analysis of Grid Architecture Via Queueing Networks.- An Effective Approach Based on Rough Set and Topic Cluster to Build Peer Communities.- Evaluation on the UbiMDR Framework.- Distributing Fixed Time Slices in Heterogeneous Networks of Workstations (NOWs).- A Grid Resources Valuation Model Using Fuzzy Real Option.- Enhancing Data Replication with Greedy Pipeline-Based Aggressive Copy Protocol in Data Grids.- A Performance Comparison of the Contiguous Allocation Strategies in 3D Mesh Connected Multicomputers.- An Enhanced Approach for PDA and Cellular Clients to Submit and Monitor Applications in the Mobile Grid.- GiPS: A Grid Portal for Executing Java Applications on Globus-Based Grids.- Advanced Grid DataBase Management with the GRelC Data Access Service.- A Generic Distributed Monitor Construct for Programming Process Synchronization in Distributed Systems.- Networks.- Low Latency Vertical Handover Using MIH L2-Trigger Algorithm in Mobile IP Networks.- SPACC: A Simple Positioning and Coverage Control Solution for Wireless Sensor Networks.- Research of Routing Algorithm in Hierarchy-Adaptive P2P Systems.- Bandwidth Degradation Policy for Adaptive Multimedia Services in Mobile Cellular Networks.- On the System Performance vs. User Movement with Systematic Simulation in Mobile Cellular Networks.- Channel Assignment and Spatial Reuse Scheduling to Improve Throughput and Enhance Fairness in Wireless Mesh Networks.- Effects of Mobility on Membership Estimation and Routing Services in Ad Hoc Networks.- Hamiltonicity and Pancyclicity of Binary Recursive Networks.- Strategies for Traffic Grooming over Logical Topologies.- Implementing IPv4+4 Addressing Architecture with IPv4 LSRR Option for Seamless Peer-to-Peer (P2P) Communication.- Dynamic Handover Mechanism Using Mobile SCTP in Contention Based Wireless Network.- A Clustering-Based Channel Assignment Algorithm and Routing Metric for Multi-channel Wireless Mesh Networks.- A Hierarchical Care-of Prefix with BUT Scheme for Nested Mobile Networks.- Some Properties of WK-Recursive and Swapped Networks.- Design and Analysis of Multicast Communication in Multidimensional Mesh Networks.- Zone Based Data Aggregation Scheduling Scheme for Maximizing Network Lifetime.- A Robust Scalable Cluster-Based Multi-hop Routing Protocol for Wireless Sensor Networks.- Qos Provisioning in Mobile Networks Based on Aggregate Bandwidth Reservation.- A Network Performance Sensitivity Metric for Parallel Applications.- The Influence of Interference Networks in QoS Parameters in a WLAN 802.11g Environment.- Software and Languages.- Instruction Selection for Subword Level Parallelism Optimizations for Application Specific Instruction Processors.- High Performance 3D Convolution for Protein Docking on IBM Blue Gene.- KSEQ: A New Scalable Synchronous I/O Multiplexing Mechanism for Event-Driven Applications.- A Synchronous Mode MPI Implementation on the Cell BETM Architecture.

An efficient algorithm for branching bisimulation and stuttering equivalence

This paper presents an efficient algorithm for the Relational Coarsest Partition with Stuttering problem (RCPS). The RCPS problem is closely related to the problem of deciding stuttering equivalence on finite state Kripke structures (see Browne, Clarke & Grumberg [3]), and to the problem of deciding branching bisimulation equivalence on finite state labelled transition systems (see Van Glabbeek & Weijland [12]). If n is the number of states and m the number of transitions, then our algorithm has time complexity O(n·(n+m)) and space complexity O(n+m). The algorithm induces algorithms for branching bisimulation and stuttering equivalence which have the same complexity. Since for Kripke structures m⩽n2, this confirms a conjecture of Browne, Clarke & Grumberg [3], that their O(n5)-time algorithm for stuttering equivalence is not optimal.

µCRL: A Toolset for Analysing Algebraic Specifications

µCRL [13] is a language for specifying and verifying distributed systems in an algebraic fashion. It targets the specification of system behaviour in a process-algebraic style and of data elements in the form of abstract data types. The µCRL toolset [21] (see http://www.cwi.nl/~mcrl) supports the analysis and manipulation of µCRL specifications. A µCRL specification can be automatically transformed into a linear process operator (LPO). All other tools in the µCRL toolset use LPOs as their starting point. The simulator allows the interactive simulation of an LPO. There are a number of tools that allow optimisations on the level of LPOs. The instantiator generates a labelled transition system (LTS) from an LPO (under the condition that it is finite-state), and the resulting LTS can be visualised, analysed and minimised.

The meaning of negative premises in transition system specifications

We present a general theory for the use of negative premises in the rules of Transition System Specifications (TSSs). We formulate a criterion that should be satisfied by a TSS in order to be meaningful, that is, to unequivocally define a transition relation. We also provide powerful techniques for proving that a TSS satisfies this criterion, meanwhile constructing this transition relation. Both the criterion and the techniques originate from logic programming [van Gelder et al. 1988; Gelfond and Lifschitz 1988] to which TSSs are close. In an appendix we provide an extensive comparison between them. As in Groote [1993], we show that the bisimulation relation induced by a TSS is a congruence, provided that it is in ntyft/ntyxt-format and can be proved meaningful using our techniques. We also considerably extend the conservativity theorems of Groote[1993] and Groote and Vaandrager [1992]. As a running example, we study the combined addition of priorities and abstraction to Basic Process Algebra (BPA). Under some reasonable conditions we show that this TSS is indeed meaningful, which could not be shown by other methods [Bloom et al. 1995; Groote 1993]. Finally, we provide a sound and complete axiomatization for this example.

An overview of the mCRL2 toolset and its recent advances

The analysis of complex distributed systems requires dedicated software tools. The mCRL language and toolset have been developed to support such analysis. We highlight changes and improvements made to the toolset in recent years. On the one hand, these affect the scope of application, which has been broadened with extended support for data structures like infinite sets and functions. On the other hand, considerable progress has been made regarding the performance of our tools for state space generation and model checking, due to improvements in symbolic reduction techniques and due to a shift towards parity game-based solving. We also discuss the software architecture of the toolset, which was well suited to accommodate the above changes, and we address a number of case studies to illustrate the approach.

Proof Theory for muCRL: A Language for Processes with Data

A simple specification language, called µCRL (micro Common Representation Language), is introduced. It consists of process algebra extended with abstract data types. The language µCRL is designed such that it contains only basic constructs with a straightforward semantics. It has been developed under the assumption that an extensive and mathematically precise study of these constructs and their interaction will yield fundamental insights that are are essential to an analytical approach of well-known and much richer specification languages. To this end, a simple property language is defined in which basic properties of processes, data and the process/data relationship can be expressed in a formal way. Next a proof system is defined for this property language, comprising a rule for induction, the Recursive Specification Principle, and process algebra axioms. The proof theory thus obtained is designed such that automatic proof checking is feasible. It is illustrated with a case study of a counter.

Invariants in Process Algebra with Data

We provide rules for calculating with invariants in process algebra with data, and illustrate these with examples. The new rules turn out to be equivalent to the well known Recursive Specification Principle which states that guarded recursive equations have at most one solution. In the setting with data this is reformulated as ‘every convergent linear process operator has at most one fixed point’ (CL-RSP). As a consequence, one can carry out verifications in well-known process algebras satisfying CL-RSP using invariants.

Focus points and convergent process operators: a proof strategy for protocol verification

We present a strategy for finding algebraic correctness proofs for communication systems. It is described in the setting of μCRL [11], which is, roughly, ACP [2,3] extended with a formal treatment of the interaction between data and processes. The strategy has already been applied successfully in [4] and [10], but was not explicitly identified as such. Moreover, the protocols that were verified in these papers were rather complex, so that the general picture was obscured by the amount of details. In this paper, the proof strategy is materialised in the form of definitions and theorems. These results reduce a large part of protocol verification to a number of trivial facts concerning data parameters occurring in implementation and specification. This greatly simplifies protocol verifications and makes our approach amenable to mechanical assistance; experiments in this direction seem promising. The strategy is illustrated by several small examples and one larger example, the Concurrent Alternating Bit Protocol (CABP). Although simple, this protocol contains a large amount of internal parallelism. so that all relevant issues make their appearance.