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...service can be seen as a set of functionalities that are available on a machine or through a network. After several attempts to design distributed programming paradigms, such as remote-procedure call =-=[1]-=-, distributed objects [2] or distributed components [3], the service paradigm seems to solve one of the main issue when dealing with distributed systems: how to design loosely-coupled distributed appl...

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...set of functionalities that are available on a machine or through a network. After several attempts to design distributed programming paradigms, such as remote-procedure call [1], distributed objects =-=[2]-=- or distributed components [3], the service paradigm seems to solve one of the main issue when dealing with distributed systems: how to design loosely-coupled distributed applications based on the com...

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... course with a larger computing granularity. Internet will provide access, acting as a bus, to a large number of processing and storage units under the form of utility computing systems such as Grids =-=[4]-=- or Cloud computers like the Google [5] and Amazon [6] ones. To conclude with this analogy, services could be considered as the “instruction set” of such distributed computing infrastructures. With su...

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...us [13], JOURNAL OF SOFTWARE, VOL. 4, NO. 7, SEPTEMBER 2009 739 © 2009 ACADEMY PUBLISHER a higher-order chemical computation model which can be seen as an higher-order extension of the Gamma language =-=[14]-=-. In HOCL, every entity is a molecule, including reaction rules. A program is a molecule, that is to say, a multiset of atoms (A1, . . . , An) which can be constants (integers, booleans, etc.), sub-so...

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...w execution. Finally, since WS-BPEL is about orchestration, workflow execution is centralized thanks to a WS-BPEL engine. One of the main drawback of WS-BPEL is its lack of formal semantics. In [16], =-=[17]-=-, a formal semantics of some of the WS-BPEL features, such as the specification of events, fault and compensation handler behaviors or transactions, are introduced. Regarding choreography, the main st...

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... by the brownian motion. Properties Chemistry Implicit parallelism Brownian Non determinism Motion We use a higher-order chemical programming language called HOCL [7]. HOCL is based on the γ-calculus =-=[13]-=-, JOURNAL OF SOFTWARE, VOL. 4, NO. 7, SEPTEMBER 2009 739 © 2009 ACADEMY PUBLISHER a higher-order chemical computation model which can be seen as an higher-order extension of the Gamma language [14]. I...

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...orkflow execution. Finally, since WS-BPEL is about orchestration, workflow execution is centralized thanks to a WS-BPEL engine. One of the main drawback of WS-BPEL is its lack of formal semantics. In =-=[16]-=-, [17], a formal semantics of some of the WS-BPEL features, such as the specification of events, fault and compensation handler behaviors or transactions, are introduced. Regarding choreography, the m...

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...ups. The motivation behind this idea is to allow asynchronous interactions between services providing a mean to implement the loose coupling concept associated with the service computing paradigm. In =-=[21]-=-, the authors describe the WSSECSPACES coordination model that extends Linda to cope with security issues. In this approach, communications do not occur directly between services and a coordination en...

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... is implicitly parallel and autonomic. It gets its inspiration from the chemical metaphor, formally represented here by a chemical language called HOCL which stands for Higher-Order Chemical Language =-=[7]-=-. In HOCL, computation is seen as reactions between molecules in a chemical solution. HOCL is higher-order: reaction rules are molecules that can be manipulated like any other molecules, i.e., HOCL pr...

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...uting promotes late binding to services. A client can bind to a service just before its invocation. Moreover, a service is usually stateless, although there was an effort to support stateful services =-=[12]-=-. This stateless aspect of services is important to design loosely-coupled distributed applications and to promote the reusability of services. Context associated with stateless services is not stored...

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...BLISHERsdoi:10.4304/jsw.4.7.738-746 Service Client Service Registry Discover Invoke Register Figure 1. Service Oriented Computing already been applied in the contexts of Grid workflow enactment =-=[9]-=-, [10] and of Desktop Grids [11] and shown its suitability to express coordination of computations. The objective of this paper is to show, through an example, that chemical programming can be a good ...

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...ation of events, fault and compensation handler behaviors or transactions, are introduced. Regarding choreography, the main standard today is the Web Service Choreography Description Language, WS-CDL =-=[18]-=-. Choreography models the interactions and dependencies between a set of services by describing their exchanges of messages. As for WS-BPEL, WS-CDL provides control structures such as sequence, parall...

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...will trigger later the execution of a service once it will be available. The tuple space is thus used as a mechanism to transfer both control and data but in an asychronous way. The work presented in =-=[22]-=- goes further in this direction by using a tuple space to support self-coordination. The main rationale for self-coordination of services is to allow asynchronous interactions during the selection and...

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...translated into a chemical setting. The enactment of workflows can also be described by a chemical program. In fact, many classical coordination mechanisms can be expressed as a chemical coordination =-=[23]-=-, [24]: sequential execution, parallel execution, mutual exclusion, atomicity, message passing, shared memory, rendez-vous, Kahn networks, etc. A very interesting property by the chemical paradigm con...

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...-746 Service Client Service Registry Discover Invoke Register Figure 1. Service Oriented Computing already been applied in the contexts of Grid workflow enactment [9], [10] and of Desktop Grids =-=[11]-=- and shown its suitability to express coordination of computations. The objective of this paper is to show, through an example, that chemical programming can be a good candidate for service programmin...

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...7, SEPTEMBER 2009 © 2009 ACADEMY PUBLISHER A. Using standards Starting from industry-led initiatives, the standard approach to compose Web Services is the Business Process Execution Language, WS-BPEL =-=[15]-=-. WS-BPEL is a language that provides several powerful control flow structures such as condition, loops, switches and activities, web services invocation, sequential and parallel composition. In addit...

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...EL, WSCDL is based on XML and thus is verbose with a low level of abstraction. B. Rewriting systems As chemical programming takes its root from rewriting systems, we can mention the work presented in =-=[19]-=- that describes a dynamic service customization and composition framework for Web services based on a rulebased service integration language with concepts borrowed from rewriting systems. Composition ...

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...ation language with concepts borrowed from rewriting systems. Composition of services using an Event-Condition-Action rule based approach, that is even closer to chemical programming, is described in =-=[20]-=-. Workflows are expressed using a set of ECA rules. The proposed approach is easy to understood for the end-users while offering an expressive way to model the coordination of complex relationships be...

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...sen non-deterministically. The execution is implicitly parallel since several reactions can occur simultaneously and it can also be seen as chaotic and possesses nice autonomic properties as shown in =-=[8]-=-. This model has 738 JOURNAL OF SOFTWARE, VOL. 4, NO. 7, SEPTEMBER 2009 © 2009 ACADEMY PUBLISHERsdoi:10.4304/jsw.4.7.738-746 Service Client Service Registry Discover Invoke Register Figure 1. Se...

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...ERsdoi:10.4304/jsw.4.7.738-746 Service Client Service Registry Discover Invoke Register Figure 1. Service Oriented Computing already been applied in the contexts of Grid workflow enactment [9], =-=[10]-=- and of Desktop Grids [11] and shown its suitability to express coordination of computations. The objective of this paper is to show, through an example, that chemical programming can be a good candid...

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...ated into a chemical setting. The enactment of workflows can also be described by a chemical program. In fact, many classical coordination mechanisms can be expressed as a chemical coordination [23], =-=[24]-=-: sequential execution, parallel execution, mutual exclusion, atomicity, message passing, shared memory, rendez-vous, Kahn networks, etc. A very interesting property by the chemical paradigm concerns ...

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...been addressed in a more general context and several solutions have been proposed to keep the computational complexity acceptable. One of these solutions is based on a structured multiset using types =-=[25]-=- that provides a way to specify relations between molecules. These relations can be used to consider only a subset of the molecules when shooting a rule instead of all molecules within a solution. Ano...

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...tions can be used to consider only a subset of the molecules when shooting a rule instead of all molecules within a solution. Another approach, based on spatial notions, has also been investigated in =-=[26]-=-. Eventually, by performing a static analysis of a chemical program, it is often possible to limit drastically the number of useless checks for reaction and thus, the number of reactions. Of course, t...