Reduction Semantics and Formal Analysis of Orc Programs

AbstractOrc is a language for orchestration of web services developed by J. Misra that offers simple, yet powerful and elegant, constructs to program sophisticated web orchestration applications. The formal semantics of Orc poses interesting challenges, because of its real-time nature and the different priorities of external and internal actions. In this paper, building upon our previous SOS semantics of Orc in rewriting logic, we present a much more efficient reduction semantics of Orc, which is provably equivalent to the SOS semantics thanks to a strong bisimulation. We view this reduction semantics as a key intermediate stage towards a future, provably correct distributed implementation of Orc, and show how it can naturally be extended to a distributed actor-like semantics. We show experiments demonstrating the much better performance of the reduction semantics when compared to the SOS semantics. Using the Maude rewriting logic language, we also illustrate how the reduction semantics can be used to endow Orc with useful formal analysis capabilities, including an LTL model checker. We illustrate these formal analysis features by means of an online auction system, which is modeled as a distributed system of actors that perform Orc computations

Rewriting Logic Semantics of a Plan Execution Language

The Plan Execution Interchange Language (PLEXIL) is a synchronous language developed by NASA to support autonomous spacecraft operations. In this paper, we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance logical engine. The rewriting logic semantics is by itself a formal interpreter of the language and can be used as a semantic benchmark for the implementation of PLEXIL executives. The implementation in Maude has the additional benefit of making available to PLEXIL designers and developers all the formal analysis and verification tools provided by Maude. The formalization of the PLEXIL semantics in rewriting logic poses an interesting challenge due to the synchronous nature of the language and the prioritized rules defining its semantics. To overcome this difficulty, we propose a general procedure for simulating synchronous set relations in rewriting logic that is sound and, for deterministic relations, complete. We also report on two issues at the design level of the original PLEXIL semantics that were identified with the help of the executable specification in Maude

Extending the Real-Time Maude Semantics of Ptolemy to Hierarchical DE Models

This paper extends our Real-Time Maude formalization of the semantics of flat Ptolemy II discrete-event (DE) models to hierarchical models, including modal models. This is a challenging task that requires combining synchronous fixed-point computations with hierarchical structure. The synthesis of a Real-Time Maude verification model from a Ptolemy II DE model, and the formal verification of the synthesized model in Real-Time Maude, have been integrated into Ptolemy II, enabling a model-engineering process that combines the convenience of Ptolemy II DE modeling and simulation with formal verification in Real-Time Maude.Comment: In Proceedings RTRTS 2010, arXiv:1009.398

Model Checking Classes of Metric LTL Properties of Object-Oriented Real-Time Maude Specifications

This paper presents a transformational approach for model checking two important classes of metric temporal logic (MTL) properties, namely, bounded response and minimum separation, for nonhierarchical object-oriented Real-Time Maude specifications. We prove the correctness of our model checking algorithms, which terminate under reasonable non-Zeno-ness assumptions when the reachable state space is finite. These new model checking features have been integrated into Real-Time Maude, and are used to analyze a network of medical devices and a 4-way traffic intersection system.Comment: In Proceedings RTRTS 2010, arXiv:1009.398

Towards verification of computation orchestration

Recently, a promising programming model called Orc has been proposed to support a structured way of orchestrating distributed Web Services. Orc is intuitive because it offers concise constructors to manage concurrent communication, time-outs, priorities, failure of Web Services or communication and so forth. The semantics of Orc is precisely defined. However, there is no automatic verification tool available to verify critical properties against Orc programs. Our goal is to verify the orchestration programs (written in Orc language) which invoke web services to achieve certain goals. To investigate this problem and build useful tools, we explore in two directions. Firstly, we define a Timed Automata semantics for the Orc language, which we prove is semantically equivalent to the operational semantics of Orc. Consequently, Timed Automata models are systematically constructed from Orc programs. The practical implication is that existing tool supports for Timed Automata, e.g., Uppaal, can be used to simulate and model check Orc programs. An experimental tool has been implemented to automate this approach. Secondly, we start with encoding the operational semantics of Orc language in Constraint Logic Programming (CLP), which allows a systematic translation from Orc to CLP. Powerful constraint solvers like CLP(R) are then used to prove traditional safety properties and beyond, e.g., reachability, deadlock-freeness, lower or upper bound of a time interval, etc. Counterexamples are generated when properties are not satisfied. Furthermore, the stepwise execution traces can be automatically generated as the simulation steps. The two different approaches give an insight into the verification problem of Web Service orchestration. The Timed Automata approach has its merits in visualized simulation and efficient verification supported by the well developed tools. On the other hand, the CPL approach gives better expressiveness in both modeling and verification. The two approaches complement each other, which gives a complete solution for the simulation and verification of Computation Orchestration

DualTable: A Hybrid Storage Model for Update Optimization in Hive

Hive is the most mature and prevalent data warehouse tool providing SQL-like interface in the Hadoop ecosystem. It is successfully used in many Internet companies and shows its value for big data processing in traditional industries. However, enterprise big data processing systems as in Smart Grid applications usually require complicated business logics and involve many data manipulation operations like updates and deletes. Hive cannot offer sufficient support for these while preserving high query performance. Hive using the Hadoop Distributed File System (HDFS) for storage cannot implement data manipulation efficiently and Hive on HBase suffers from poor query performance even though it can support faster data manipulation.There is a project based on Hive issue Hive-5317 to support update operations, but it has not been finished in Hive's latest version. Since this ACID compliant extension adopts same data storage format on HDFS, the update performance problem is not solved. In this paper, we propose a hybrid storage model called DualTable, which combines the efficient streaming reads of HDFS and the random write capability of HBase. Hive on DualTable provides better data manipulation support and preserves query performance at the same time. Experiments on a TPC-H data set and on a real smart grid data set show that Hive on DualTable is up to 10 times faster than Hive when executing update and delete operations.Comment: accepted by industry session of ICDE201

Twenty years of rewriting logic

AbstractRewriting logic is a simple computational logic that can naturally express both concurrent computation and logical deduction with great generality. This paper provides a gentle, intuitive introduction to its main ideas, as well as a survey of the work that many researchers have carried out over the last twenty years in advancing: (i) its foundations; (ii) its semantic framework and logical framework uses; (iii) its language implementations and its formal tools; and (iv) its many applications to automated deduction, software and hardware specification and verification, security, real-time and cyber-physical systems, probabilistic systems, bioinformatics and chemical systems