Mumbai University > Computer engineering > Sem 7 > Software Architecture.

Marks: 10 M

Year: Dec14, Dec13, May13, Dec12, May12

• Service-oriented architectures are directed at supporting business enterprises on the internet. From an architectural perspective, participating organizations on the internet present a virtual machine layer of services of which users may avail them. The various SOA services corresponding to functions in classical virtual machine architecture are offered by different controlling agencies. The challenge is to provide the necessary support to a client who wants to use the service-network to achieve its goals. Web services responds to this challenge by offering a range of approaches, standards and technologies. It is necessary to:

1. Describe the components- i.e. the services
2. Determine the types of connectors to use- i.e. how the services will communicate and interact
3. Describing the application as a whole- i.e. how the various services are coordinated to achieve the business goals.

• The services of SOA are simply independent components. They have an interface describing what operations they provide. They have their own thread of control. Services can be described in Web services using WSDL- Web Service Description Language. WSDL describes services using XML as a collection of operations that may b performed on typed data sent to or from the service. Their interfaces may be described by APIs written in some programming language.

• Connectors are most interesting part of SOA. The simplest mechanism used by SOA is asynchronous event notification.

• A service requestor sends an XML document to a service provider across the network. The obligation on both parties is that XML document be structured so that both understand it. The service provider may take some action upon receiving and reading the document but there is no obligation for the provider to return anything to the requestor.

• In the next model, the connection is asynchronous request response model, resembling a remote procedure call or a distributed object method invocation.

• One key point is that interactions do not have the same semantics. The presence of agency issues, interaction based upon XML document exchange and absence of various programming semantics are the bases for the difference. SOA demands that an ADL which is executable be used. Thus formality and complete semantics are required.
• An SOA application could be described in a generic scripting language. A language that allows effective expression of business workflows is a better choice. One language used is WS-BPEL- the Web Service Business Process Execution Language. It is a scripting language that is compositional, BPEL program can appear as a service in another workflow. The language is statically typed and expressed in XML.
• The complexity in SOA model arises due to the attempt to simultaneously satisfy many goals like interoperability across heterogeneous platforms while coping with difficulties inherent in open, decentralized systems. Many decentralized enterprise application developers base their designs on REST. Web services can be offered to developers either in REST form or SOAP/ web service interface.