Qusay H. Mahmoud CIS* CIS* Service-Oriented Computing Qusay H. Mahmoud, Ph.D.

Qusay H. Mahmoud CIS* Topics Service Composition BPEL (Business Process Execution Language) Orchestration and Choreography

Qusay H. Mahmoud CIS* Service Composition Problem: more than one service might be needed to achieve a given objective –All such services need to interact seamlessly to achieve the objective Composite Web Services –Individual components implemented by different services and located at different locations –Execute in different contexts and containers –Need to interact to achieve an objective Benefits –Services can be reused –Access to high-level complex services

Qusay H. Mahmoud CIS* Service Composition Approaches –Static composition By hand BPEL4WS –Dynamic composition Model-driven –Semantic approach (OWL-S, DAML-S): Will discuss later –Example: Use WSDL for the interface Interaction of messages between WS using BPEL or WSCL Composition process involves: –Specifying the role of each participating WS –Specifying logical flow of messages between them

Qusay H. Mahmoud CIS* Service Composition Services execute in different containers separated by firewalls and trust barriers Some of the key requirements that a composition approach must satisfy (e.g. scalability, dependability, correctness) Requirements (from paper in references) that composition approach should guarantee –Connectivity –Non-functional QoS properties –Correctness –Scalability Why need such requirements? –Consider a service composed of two trusted services from different providers, is the composed service trusted?

Qusay H. Mahmoud CIS* Service Composition Requirements Connectivity –Must be reliable to determine which services are composed and reason about input/output messages Non-functional QoS properties –Based on message passing, thus needs to address Performance, security, dependability Correctness –Verification of the composed service’s properties Scalability –Multiple services will be involved, composition framework must scale with the number of composed services

Qusay H. Mahmoud CIS* Composition Approaches First generation –IBM’s Web Service Flow Language (WSFL) –BEA Systems’ Web Services Choreography Interface (WSCI) –They are incompatible Second generation –Business Process Execution Language for Web Services (BPEL4WS or BPEL): combines WSFL and WSCI with Microsoft’s XLANG

Qusay H. Mahmoud CIS* BPEL An XML-based language for process-oriented service composition Developed by IBM, BEA, Microsoft, SAP, and Siebel. Being standardized by OASIS Approach: –Interact with a Web services’ subset to achieve a given task –Composition result is called a “process”, participating services are “partners”, message exchange or intermediate result transformation are “activities” –A process interacts with external partner services through a WSDL interface

Qusay H. Mahmoud CIS* BPEL To define a process, use: –A BPEL source file (.bpel) that describes activities –A process interface (.wsdl) that describes ports of a composed service –An optional deployment descriptor (.xml) that contains the partner services’ physical locations Several element groups, the basic ones are: –Process initiation: –Process initiation: –Participating services: –Participating services: –Synchronous and Asynchronous calls: and … –Synchronous and Asynchronous calls: and … –Intermediate variables:,, –Intermediate variables:,, –Error handling:, –Error handling:, –Sequential and parallel execution:, –Sequential and parallel execution:, –Logic control: –Logic control:

Qusay H. Mahmoud CIS* BPEL Process flow (basic and structured activities) Source: C. Peltz;Web Services Orchestration and Choreography, IEEE Computer, Oct 2003, pp

Qusay H. Mahmoud CIS* BPEL Example: Model the composition of 3 services: A is called asynchronously and starts a process. B and C are called in parallel using A’s output as their input. The process waits for their completion and then makes a decision based on the results –Not all code is shown –Assumption: All services offer only one operation at one port

Qusay H. Mahmoud CIS* BPEL Code (source: Milanovic, N.; Malek, M.; Current Solutions for Web Service Composition, IEEE Internet Computing, Nov/Dec 2004, pp )

Qusay H. Mahmoud CIS* BPEL …Code

Qusay H. Mahmoud CIS* BPEL …code…

Qusay H. Mahmoud CIS* BPEL BPELJ: Allows developers to include Java code inside BPEL code BPEL can be used with two other specifications: –Web Services-Coordination: Coordinates Web services’ actions when an agreement must be reached –Web Services-Transactions: Defines Web services’ transactional behavior Several BPEL orchestration server implementations for Java EE and.NET are available including: –IBM WebSphere –Oracle BPEL Process Manager (formerly Collaxa BPEL) –Microsoft BizTalk –OpenStorm ChoreServer –Active BPEL

Qusay H. Mahmoud CIS* Orchestration and Choreography Describe two aspects of creating business processes from composite Web services Orchestration: represents control from one party’s perspective Choreography: tracks the message sequence among multiple parties Source: C. Peltz; Web Services Orchestration and Choreography, IEEE Computer, Oct 2003, pp

Qusay H. Mahmoud CIS* WSCI Web Services Choreography Interface –Developed by Sun, SAP, BEA, and Intalio –Defines a collaboration extension to WSDL –Defines the overall choreography or message exchange between Web services –Describes only the observable behavior and doesn’t address the definition of executable business processes as BPEL does –A WSCI choreography would include a set of WSCI interfaces, one for each partner in the interaction –No single process manages the interaction

Qusay H. Mahmoud CIS* WSCI Each WSCI action represents a unit of work that maps to a specific WSDL operation Extends WSDL to describe how to choreography the available WSDL operations –WSDL describes the entry points for each available service, and WSCI describes the interactions among WSDL operations Supports basic and structured activities –An “action” tag defines a basic request/response msg –Each activity specifies the WSDL operation involved and the specific participant that performs it –A choreography invokes external services through a “call” tag

Qusay H. Mahmoud CIS* WSCI Example: Create a purchasing process that contains two sequential activities, Receive Order and Confirm. Each activity maps to a WSDL portType, and WSCI establishes a correlation between them Source: C. Peltz; Web Services Orchestration and Choreography, IEEE Computer, Oct 2003, pp