Realisation of SOA using Web Services Advanced WS Adomas Svirskas Vilnius University December 2005.

Realisation of SOAusing Web Services

Advanced WS

Adomas Svirskas

Vilnius University

December 2005

Agenda

• WS-* Specifications

• Advanced WS Architecture

• WS Taxonomy

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

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

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.

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?

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

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.

Messages, Services, UoW [1]

J-J Dubray, SAP Blog http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/2261

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

WS-* Standards Architecture [1]

J-J Dubray, SAP Blog http://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/wlg/2261

WS-* Standards Architecture (W3C)

Web Services Architecture, W3C, http://www.w3.org/TR/ws-arch/#technology

WS-* Standards Architecture – M$

http://msdn.microsoft.com/webservices/webservices/understanding/specs/default.aspx

WS-* Standards Architecture - IBM

http://www-128.ibm.com/developerworks/webservices/standards/

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.

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.

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.

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.

WS Choreography

http://www.w3.org/TR/ws-cdl-10/#Purpose-of-WS-CDL

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

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

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

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/