Tutorials : Service Oriented Architecture - Part 2 :

The Process

In the previous article of this series, we have outlined guidelines on identifying the reusable business processes across the organizations boundary. The outcome of this process can lead to the basic building blocks or Components that co-exist within an organization and perform one or more business operations.

• Component Specification: In a technology neutral way like UML define the business functions. This must be technology independent. This just specifies what the interfaces are that the Component offers and what the Component dependencies are.
• Interface Definition: Translation of the Functional Specification in a target platform language in a technology neutral way. For example, the interfaces can be elaborated using UML and translated into a programming language of choice such as Java.
• Service Specification: Subscribing to 1..* functional interfaces. Services can collate multiple Component interfaces to provide a coarse-grained Service Definition. Again, this needs to be technology neutral.
• Service Discovery and Registry: A mechanism for Registering Services to a registry. The Consumers use a Service Discovery mechanism and access the Services by looking up in the registry.
• Technology binding: Consumer Components are inherently technology independent. We need to plug-in a technology binding mechanism to use a certain kind of interface exposed by the Service provider and its runtime instance technology. For example, we need to plug-in a technology layer into the Service Consumer to access a Service by using EJB or by using Web Service mechanism as is appropriate. We will elaborate on this later in this article.

The following small example will clear the clouds. Let us assume that in a company we are to write a Payroll Management System which manages the Employee payroll records and posts the pay- slips to their home addresses using the Address manager component. Also there is another Component which looks after the employee welfare and sends out a gift check on the anniversary or birthdays of employees.

The component specification of the above components can be shown as in Figure-1.

Figure-1 The Component Specification

Let us consider that we might want to offer a Service at a higher level called the “EmployeeService”, which can subscribe to both the Payroll Management and Welfare Management interfaces. The Service Definition for the EmployeeService might look like the following in Figure-2.

Figure-2 The Service Specification

The interface definitions are still technology independent but can be translated in to a specific programming language such as Java. For example, the interface definition for the EmployeeService can look like the following in Java (Listing - 1). We have omitted the data type references from the diagram for simplicity

public interface IEmployeeManger {
   void sendPayslip(IEmployee employee, IDocument payslip) 
				throws EmployeeNotFoundException, 
ServiceUnavailableException;

   void sendGiftCheck(IEmployee employee, IDocument check) throw
 EmployeeNotFoundException,ServiceUnavailableException;
}

Note: The Exceptions listed above are very much application specific exceptions and avoid any technology specific exceptions.

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