- This document briefly describes simpA-WS, a Javabased agent-oriented computing technology to flexibly and effectively implement WS-I compliant SOA/WS applications-i.e. Web-Service applications with a Service-Oriented Architectureboth on the user side and the service side.
I. INTRODUCTION
simpA-WS is a Java-based technology that makes it
possible to build WS-I SOA/WS compliant applications adopting an
agent-oriented style in designing and developing the systems.
simpA-WS is based on of simpA model and technology
[
On the one side, simpA-WS provides a framework API to
build user applications in terms of sets of agents that flexibly
interact and use Web Services compliant with the WS-I Basic
Profile [
To tackle the complexity of modern and future software
systems, simpA introduces agents and artifacts as
highlevel abstractions to design and build distributed / concurrent
software systems. This is the A&A (Agents and Artifact)
conceptual model [
A&A metaphors are taken from human cooperative working environments, where “systems” are composed by individual autonomous entities which pro-actively carry on some kind of activities or tasks, both individual and cooperative, typically requiring forms of interaction and coordination with other individuals. A fundamental aspect of such a picture is the context —or the environment— that makes it possibile to such activities to take place. Artifacts designed and built by humans are an essential part of such a context, both as outcome of the activities and as the tools exploited by humans to support and realise them. Artifacts can be then resources and objects constructed during the activities, but also whatever tools is used to support humans communication, coordination, and— more generally—cooperative working activities. The overall picture is given by workspaces where ensembles of individuals work and interact in a coordinated manner, by communicating and sharing / using the same artifacts, so as to achieve some kind of objective.
A&A brings this metaphor down to software engineering, conceiving a software system as one or multiple workspaces where ensembles of autonomous entities—the agents—execute their working activities and interact by co-constructing, sharing and using artifacts, analogously to the human case.
simpA provides agents and artifacts as basic high-level building blocks to decompose and structure complex systems, in particular: • agents are provided as first-class abstractions to model and design pro-active entities, i.e. entites programmed so as to autonomously execute some kind activity— composed by one or more tasks—encapsulating the control of such activities; • artifacts are provided as first-class abstractions to model and design what is used or constructed by agents during their activities, including resources, tools, devices: any passive entity encapsulating some kind of functionality, exposed by a proper interface; • workspaces are the logical place where agents and artifacts are immersed, used to give a topology to the overall activities, and then partition the application environment. Objects and classes are used as basic abstractions to define data structures to build agents and artifacts.
B. A&A for Implementing SOA / Web Service Applications
simpA-WS makes it possible to exploit the A&A approach
and simpA for implementing SOA and Web-Service
applications, following the basic architectured described in W3C
documentation [
Using simpA-WS both service users and providers are modelled as simpA agents, as pro-active entities that respectively (i) need to access and use services in their working activities, encapsulating the business logic of user applications, and (ii) process the requests and messages for services, encapsulating the service business logic. In both cases, artifacts are used as high-level mediating entities functioning as interfaces, encapsulating the technology needed to enable the interaction using WS-* standards. In particular (refer to Fig. 2 and Fig. 3): • on the user side, a specific kind of artifacts – called WSArtifact — is provided to make it possible for simpA
Agent Agent
Agent
WS-Artifact con WSDL X WS-Artifact con WSDL Y
Environment simpA
AXIS2 simpA-WS
tuProlog
Java / JVM 5.0
WS-USER APPLICATION WS Msgs, requests responses
Web Servìce Container + the meta-ws dynamicaly configured with WSDL X simpa-WS meta-ws AXISC2oWnetabinSeerrvice
Tomcat 5.0.5 Java / JVM 5.0 tuple centres TuCSoN Infrastructure
Java / JVM 5.0 agents to access and use what ever existing Web Service, by simply creating and using instances of such an artifact; • on the service side, artifacts called Service-Artifacts are provided to make it possible for simpA agents to get and process the messages delivered to a specific Web Service, again by simply creating and using instances of such an artifact.
The adoption of the agent level of abstraction, and in particular
of agents and artifacts basic building blocks, makes it possible
to exploit a fully uncoupled approach for modelling and
realising interaction with Web Services, as required by true
serviceoriented architecture [
Currently simpA-WS can run on any Java-based platform, version 5.0. Consequently, it can be seamlessly deployed on machines with different kind of operating systems and hardware configuration. A light-weight version is planned, in order to port simpA-WS—the API for implementing user application in particular—on J2ME, the Java platform for mobile devices, so as to implement user applications on top of J2ME-enabled smart phones / devices.
Fig. 2 and Fig. 3 provide an overview of the architecture of the simpA-WS technology, respectively on the user side and the service side. Fig. 4 shows a mixed and articulated case, where services are themselves users of other services.
simpA and simpA-WS are fully developed in Java, and
exploit apache Axis2 open-source libraries [
simpA and simpA-WS internally exploits tuProlog [
Among the examples provided with simpA-WS
distribution, a supply-chain sample application is provided, following
the reference sample application defined by WS-I organisation,
available among the deliverables at WS-I Web Site [
ServiceArtifact configured with WSDL X Environment Agent
Agent Agent SERVICE APPLICATION
APPLICATIONS simpA-WS is one of the technologies experimented for implementing SOA-based applications in the context of STIL (“Strumenti Telematici per l’Interoperabilita` delle reti di imprese: Logistica digitale integrata per l’Emilia-Romagna”).
STIL is a 2-years project funded by Emilia-Romagna, in the
context of the “Iniziativa 1.1 del Piano Telematico Regionale”
initiative [
For the purpose, a SOA-based infrastructure has been
conceived, designed and implemented to enable interoperability
among the different participants. The STIL infrastructure is
meant to provide an effective support for enabling
communication, coordination and cooperation among the open and
heterogeneous kind of WS-based applications and services.
simpA-WS is currently experimented as one of the
stateof-the-art technologies for implementing the applications and
services, and first results are available on STIL web sites [
VI. INDUSTRIAL SUPPORT AND DISTRIBUTION
simpA and simpA-WS are open-source projects, and can be
freely downloaded and used for research and non-commercial
purposes from related web sites [