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Realisation of SOAusing Web Services
Advanced WS
Adomas Svirskas
Vilnius University
December 2005
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Agenda
• WS-* Specifications
• Advanced WS Architecture
• WS Taxonomy
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Why the WS core is not enough?
• We have got SOAP, WSDL, UDDI
• So we can develop, publish, discover, invoke Web Services
• But... this is about application integration
• While the business world needs business process integration
• Thus we need composable, orchestrated, transactable, secure Web Services
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Current State of WS [1]
• The Web Services stack of standards has grown rapidly in the last three years from its original form as SOAP, WSDL and UDDI specifications
• With it, the Web is moving towards being an open distributed computing platform with which we can build Service Oriented Architectures and Composite Applications
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The Reality - WS-Nonexistent Standards [2]
• The numerous WS specifications introduced by various parties over the past few years show that there's a clear desire to fill out the WS architecture stack
• Unfortunately, converting those specifications into actual industry standards is elusive
• WS-This and WS-That– The specifications (collectively known as WS-*) are numerous
and daunting.– A coalition of developers and architects from BEA Systems, IBM,
and Microsoft authored most of them, though different specifications also include contributions from several other smaller companies.
– Because the same author companies didn't write all the specifications, at least two different lists exist.
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The Reality - WS-Nonexistent Standards [2]
• One can find complete lists of the WS-* specifications at:– http://msdn.microsoft.com/Webservices/understanding/specs– http://www-128.ibm.com/developerworks/webservices/
standards/– http://dev2dev.bea.com/webservices/standards.html
• Natural questions:– How do these specifications fit together?– Are they all really necessary?– If they are necessary, how and when will they
become actual standards?
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WS-*• These lists from Microsoft, IBM and BEA (there are more lists) cover pretty much every topic
imaginable:– WS-Addressing– WS-Attachments– WS-BusinessActivity– WS-Coordination– WS-Discovery– WS-Enumeration– WS-Eventing– WS-Federation– WS-Inspection– WS-Manageability– WS-MetadataExchange– WS-Notification– WS-PolicyFramework– WS-Provisioning– WS-ReliableMessaging– WS-Resource– WS-Security– WS-Topics– WS-Transactions– WS-Transfer
• Moreover, some areas have two, three, or more specifications devoted to them• There is a need for taxonomy of WS-* specs
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Current State of WS [1]
• Within Web-based platform, software agents may– Exchange messages– Provide or consume services– Perform cooperatively units of work
• Message exchanges and operation invocations may be part of a unit of work performed by software agents.
• Instances of this unit of work have a precise lifecycle and often have a context.
• Service compositions represent a particular type of unit of work.
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Messages, Services, UoW [1]
J-J Dubray, SAP Blog http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/2261
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Web Services Taxonomy [1]
• All standards and (the proposed specs) developed as part of the Web Services stack fall in one of these three categories
• At the message exchange level, the message exchange protocol (SOAP) is layered on top of transport and syntax specifications. This protocol can be composed with other specifications for reliable and/or secure message exchanges
• The WS-Addressing specification standardizes addressing mechanisms for the protocol
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WS-* Standards Architecture [1]
J-J Dubray, SAP Blog http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/2261
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WS-* Standards Architecture (W3C)
Web Services Architecture, W3C, http://www.w3.org/TR/ws-arch/#technology
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WS-* Standards Architecture – M$
http://msdn.microsoft.com/webservices/webservices/understanding/specs/default.aspx
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WS-* Standards Architecture - IBM
http://www-128.ibm.com/developerworks/webservices/standards/
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Web Services Taxonomy [1]
• At the service level, the service definition specification (WSDL) can be composed with other specifications to add the concepts of Event and Resource
• A directory (UDDI) may be used to store, search and retrieve service definitions.
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WS Taxonomy – UoW [1]
• WS- RemotePortlets specification provides a service interface to user activities.
• The foundation of the unit of work level is composed of Context, Lifecycle and optionally Coordination services for a particular type of unit of work.
• The most basic type is a transaction: WS-AtomicTransaction (WS-AT), WS-Business Activity (WS-BA).
• WS-BPEL provides more sophisticated capabilities and can be used to specify service compositions.
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WS Choreography
• Finally, WS-CDL has the capability to describe any message exchanges performed by an arbitrary number of participants
• WS-CDL is a choreography language as opposed to WS-BPEL which is an orchestration language. WS-BPEL is executable, WS-CDL is not.
• In a choreography, it is the mere exchange of messages by agents which advances the state of the choreography.
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WS Choreography
• The decision process by which an agent decides to send a message is hidden from the choreography definition.
• In an orchestration, an engine decides what to do next when it receives or sends a message, based on an orchestration definition.
• A choreography definition may be used by each participant to configure the validation of the current message exchange instead of hard coding it.
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WS Choreography
http://www.w3.org/TR/ws-cdl-10/#Purpose-of-WS-CDL
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WS-* Standards Architecture
• The architecture is complemented by security (WS-Security, SAML ,…), management (WS-DM) and metadata (WS-Policy) specifications
• Overall, these specifications have enabled the web to become a powerful distributed computing platform
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Service Component Architecture (SCA)
• A major news as of 30 November: SAP, IBM, BEA, Oracle, IONA, Sybase, Siebel an others have announced the development of a new component model specifically designed for building service oriented architectures - SCA
• SCA is a new component model based on the principles of Service Oriented Architecture– middleware and programming language neutral– offers a superior application model to support "Rich
Clients" and construct RIAs (Rich Internet Applications)
• http://dev2dev.bea.com/pub/a/2005/11/sca.html
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Service Component Architecture (SCA)
• SCA is also an assembly mechanism, based on the injection of dependency pattern (as in Spring framework) to create Modules from Components and Systems and Subsystems from Modules.
• A module is composed of service components which run in the same process.
• As such, SCA provides the means to compose assets which have been implemented using a variety of technologies as services can be accessed and reused in a uniform manner
• Any component developed with SCA should be able to participate in a system with any other SCA component, regardless of its implementation language
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References• [1] Dubray, J-J, SAP Blog 2005. Taxonomy and Architecture of Web
Service Standards, http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/2261
• [2] Vinoski, S. WS-Nonexistent Standards. IEEE's Internet Computing, November 2004. http://www.iona.com/hyplan/vinoski/pdfs/IEEE-WS-NonexistentStandards.pdf
• [3] Ferguson, D. et al. Secure, Reliable, Transacted Web Services: Architecture and Composition, 2003. http://www-306.ibm.com/software/solutions/webservices/pdf/SecureReliableTransactedWSAction.pdf
• Papazoglou, M., Dubray, J-J. A Survey of Web service technologies. 2004, http://eprints.biblio.unitn.it/archive/00000586/