Tau Be or not Tau Be? - A Perspective on Service Compatibility and Substitutability

One of the main open research issues in Service Oriented Computing is to propose automated techniques to analyse service interfaces. A first problem, called compatibility, aims at determining whether a set of services (two in this paper) can be composed together and interact with each other as expected. Another related problem is to check the substitutability of one service with another. These problems are especially difficult when behavioural descriptions (i.e., message calls and their ordering) are taken into account in service interfaces. Interfaces should capture as faithfully as possible the service behaviour to make their automated analysis possible while not exhibiting implementation details. In this position paper, we choose Labelled Transition Systems to specify the behavioural part of service interfaces. In particular, we show that internal behaviours (tau transitions) are necessary in these transition systems in order to detect subtle errors that may occur when composing a set of services together. We also show that tau transitions should be handled differently in the compatibility and substitutability problem: the former problem requires to check if the compatibility is preserved every time a tau transition is traversed in one interface, whereas the latter requires a precise analysis of tau branchings in order to make the substitution preserve the properties (e.g., a compatibility notion) which were ensured before replacement.Comment: In Proceedings WCSI 2010, arXiv:1010.233

Dynamic replication strategies in data grid systems: A survey

In data grid systems, data replication aims to increase availability, fault tolerance, load balancing and scalability while reducing bandwidth consumption, and job execution time. Several classification schemes for data replication were proposed in the literature, (i) static vs. dynamic, (ii) centralized vs. decentralized, (iii) push vs. pull, and (iv) objective function based. Dynamic data replication is a form of data replication that is performed with respect to the changing conditions of the grid environment. In this paper, we present a survey of recent dynamic data replication strategies. We study and classify these strategies by taking the target data grid architecture as the sole classifier. We discuss the key points of the studied strategies and provide feature comparison of them according to important metrics. Furthermore, the impact of data grid architecture on dynamic replication performance is investigated in a simulation study. Finally, some important issues and open research problems in the area are pointed out

INHIBITION EFFECT OF FLAVONOID EXTRACT OF Euphorbia Guyoniana ON THE CORROSION OF MILD STEEL IN H2SO4 MEDIUM

<p>The influence of flavonoids extracts of three parts of <em>Euphorbia Guyoniana</em> towards the corrosion of type API 5L X52 steel in 15% H₂SO₄ has been evaluated by weight loss method and polarization technique. The results showed that extracts are a good inhibitors for API 5L X52 steel in this medium. The corrosion inhibition efficiency increases on increasing plant extracts concentration. The inhibition is attributed to the adsorption of the surface of the metal. Potentiodynamic polarization results revealed that the studied inhibitors behave as a mixed type.</p

SLA-driven resource re-allocation for SQL-like queries in the cloud

International audienceCloud computing has become a widely used environment for database querying. In this context, the goal of a query optimizer is to satisfy the needs of tenants and maximize the provider’s benefit. Resource allocation is an important step toward achieving this goal. Allocation methods are based on analytical formulas and statistics collected from a catalog to estimate the cost of various possible allocations and then choose the best one. However, the allocation initially chosen is not necessarily the optimal one because of the approximate nature of the analytical formulas and the fact that the catalog may not be up to date. To solve this problem, existing work was proposed to collect statistics during the execution of the query and then trigger a re-allocation if suboptimality is detected. However, these proposals consider that queries have the same level of priority. Unlike the existing work, we propose in this paper a method of statistics collector placement and resource re-allocation by taking into account that the cloud is a multi-tenant environment and queries have different services-level agreements. In the experimental section, we show that our method provides a better benefit for the provider compared to state-of-the-art methods