Towards a Programming Model for Service-Oriented Computing

composition model is built on top of component models. We look for a customization without source code modification.

Composition

• behavioral
• adaptation -> point of variability
  
• structural
• mediation -> message processing

Dynamic Binding

• dependency injection -> automatic dependency resolution
• Mediation Model -> dynamic mediation -> dynamic binding

IMPORTANT DEFINITION: a service is a visible access point to a component. A component can offer multiple services or reference multiple services

service specification -> access channel

• interface -> WSDL
  
• policies
• behavioral description -> BPEL

service component implementation (similar to the SCA model in which we have comonent, composite, reference, services, properties)

• service spec: characteristics of a service
• required services
• service properties
• container directives
• implementation artefacts

service component

• Name
• implementation
• values for properties
• specification + resolution for services
• wires + queries + QoS policies

directives for service composition could be instructed using either Pragmas or Control files

• Control Files: BPEL or other workflow descriptions
• Pragmas: Annotations within the code

Structural Composition (Mediation)

• wiring: wires represent the flow of messages
• Bundle -> a collection of services
• Event-Driven Composition
• Mediation
• Content-based Routing
• Transformation -> transform and map messages
• Augmentation -> adding additional information to the message
• Side Effect -> extra operation on the messages
  

Behavioral Composition - Process Oriented (Adaptation)

• workflow oriented
• state machine
• UML state diagram
• BPEL -> DAG activity nodes
• short running
• long running
• has one or more interfaces
• different implementations for canceling

SDO (Service Data Object) = a uniform way of representing service data + the abstract tree is used to access data irrespective of how it is provided

IMPORTANT

SOA component model improves over CORBA/J2EE/COM

• control language
• XSD & WSDL are more tolerant of interface evaluation
• call/return + one way messaging
• rich contracts
• QoS
• behavioral description
• mediation + intermediaries

SCA -> abstraction of implementation concerns
Web Services -> abstraction for interoperability concerns