Starting this month, to meet the needs of our readers we are introducing a new page for Frequently Asked Questions that will be addressed by our esteemed editorial board. No topic is too basic or too advanced to be discussed here. Please send us your queries and we will provide you with accurate and up-to-date information on topics related to XML, service-oriented architecture, and Web services. If you have a question pertinent to this space, please send it to WSJFAQ@sys-con.com.

1.  What is the relationship between service-oriented architecture and Web services? Doesn't SOA automatically imply Web services?

A common misconception is that SOA implies Web services. This is grossly incorrect. SOA is a concept. Web services are a technology or technology platform. Service-oriented architecture is a methodology for achieving application interoperability and reuse of IT assets to enable business agility. It encapsulates governance, process, modeling, and tools to align business functionality requirements with the technical capabilities of the underlying software platform. The basic idea behind SOA is the realignment of application architecture around reuse, efficiency, technology independence (decoupling of technology and business functionality), and flexibility to enable maintainability. SOA is neither a technology nor a technology standard; rather it's a high-level concept that enables the development of a service-based architecture blueprint.

SOA, as the name implies, is based around the concept of a service. The building blocks for achieving an SOA are an application front end, a service that is exposed via a service bus, and a service repository. In today's industry, there are four trends that have converged to facilitate a service-oriented enterprise - Business Process Management (realization of the business), SOA (enablement of business agility), Web services (a natural platform to service-enable the enterprise), and XML (the underlying technology). This is shown in Figure 1.

While SOA is a concept, in order to implement an SOA, a technology platform is required. The most feasible option for this in the industry today is Web services. The requirements for realizing an SOA are the standards, a standard interoperability protocol, a standard API for defining the services, and a universal repository. Web services constitute a technology platform that fulfils all of these requirements.

2.  What is a Web Services-Oriented Architecture?

When SOA is implemented using the Web services technology, it is called a Web Services-Oriented Architecture (see Figure 2). In his WSJ article "Web Services-Oriented Architecture: A Critical Technology" (http://webservices.sys-con.com.read/39471.htm), Ashish Deshpande describes the challenges in building a WSOA. While Web services are not the only option for building SOAs, they are the most prevalent and feasible option available to organizations today. Gartner predicts that by 2008, SOA and Web services will be implemented together in more than 75 percent of new SOA or Web services projects.

3.  Can SOA be implemented without Web services?

Absolutely! SOA is not a new concept - it's just that technology has recently come full circle to provide optimal platforms for building service-oriented architectures. In fact, the main message behind SOA is not the "Web" but rather the "service." The main objective of SOA is to help organizations move towards a service-oriented enterprise (SOE). An alternative to leveraging Web services is to base your SOA around messaging products. In their current incarnation, messaging vendors are offering Enterprise Service Buses (ESBs) that enable accessing services in an SOA via different means: API calls, messaging, as well as Web services.