Service-Oriented Architecture (SOA) and Web Services: The Road to Enterprise Application Integration (EAI)

by Qusay H. Mahmoud, April 2010

Most enterprises have made extensive investments in system resources over the course of many years. Such enterprises have an enormous amount of data stored in legacy enterprise information systems (EIS), so it's not practical to discard existing systems. It's more cost-effective to evolve and enhance EIS. But how can this be done? Service Oriented Architecture (SOA) provides a cost-effective solution.

SOA is not a new concept. Sun defined SOA in the late 1990's to describe Jini, which is an environment for dynamic discovery and use of services over a network. Web services have taken the concept of services introduced by Jini technology and implemented it as services delivered over the web using technologies such as XML, Web Services Description Language (WSDL), Simple Object Access Protocol (SOAP), and Universal Description, Discovery, and Integration(UDDI). SOA is emerging as the premier integration and architecture framework in today's complex and heterogeneous computing environment. Previous attempts didn't enable open interoperable solutions, but relied on proprietary APIs and required a high degree of coordination between groups. SOA can help organizations streamline processes so that they can do business more efficiently, and adapt to changing needs and competition, enabling thesoftware as a service concept. eBay for example, is opening up its web services API for its online auction. The goal is to drive developers to make money around the eBay platform. Through the new APIs, developers can build custom applications that link to the online auction site and allow applications to submit items for sale. Such applications are typically aimed at sellers, since buyers must still head to ebay.com to bid on items. This type of strategy, however, will increase the customer base for eBay.

SOA and web services are two different things, but web services are the preferred standards-based way to realize SOA. This article provides an overview of SOA and the role of web services in realizing it. The article provides:

• An overview of software as a service
• A tutorial on SOA
• An overview of Sun's platforms for building web services
• Guidelines for designing interoperable web services
• Challenges in moving to SOA
• An overview of Java Business Integration (JSR 208)
• A discussion of web services for enterprise application integration

Service-Oriented Architecture

SOA is an architectural style for building software applications that use services available in a network such as the web. It promotes loose coupling between software components so that they can be reused. Applications in SOA are built based on services. A service is an implementation of a well-defined business functionality, and such services can then be consumed by clients in different applications or business processes.

SOA allows for the reuse of existing assets where new services can be created from an existing IT infrastructure of systems. In other words, it enables businesses to leverage existing investments by allowing them to reuse existing applications, and promises interoperability between heterogeneous applications and technologies. SOA provides a level of flexibility that wasn't possible before in the sense that:

• Services are software components with well-defined interfaces that are implementation-independent. An important aspect of SOA is the separation of the service interface (the what) from its implementation (the how). Such services are consumed by clients that are not concerned with how these services will execute their requests.
• Services are self-contained (perform predetermined tasks) and loosely coupled (for independence)
• Services can be dynamically discovered
• Composite services can be built from aggregates of other services

SOA uses the find-bind-execute paradigm as shown in Figure 1. In this paradigm, service providers register their service in a public registry. This registry is used by consumers to find services that match certain criteria. If the registry has such a service, it provides the consumer with a contract and an endpoint address for that service.