Exactly what is a Service-Oriented Architecture, and what makes an SOA different from Web services? The first thing to understand is that Web services tools and technologies are at the heart of most current SOA definitions and implementations.
The basic idea behind Web services is that, using standard protocols and languages such as the Extensible Markup Language (XML), historically large, monolithic blocks of software-such as ERP systems-can be broken up into smaller, modular, loosely-coupled bits of code. Each of these modular building blocks can be accessed by, and exchange data and transactions with, other modular building blocks. Therefore, they are said to act as network-based services. These so-called Web services can be combined and composed into composite applications.
There are several advantages to this type of architecture. First, these types of modular Web-based services, because they are self-contained and because they interact with one another in standard ways using standard protocols, can be easily reused. Take, for example, a consumer products company that collects customer information through various channels such as the Internet, call centers and retail. A single Web service that validated and cleansed consumer information as it was entered could be used by systems supporting each of those channels. The manufacturing company would be able to avoid buying or writing data validation and cleansing software into each of its customer-facing applications. Also, because those applications were using the same service and the same algorithms for consumer data validation and cleansing, customer information would be more consistent.
Particularly compared to traditional large, monolithic systems, Web services also can be easier and quicker to change and easier to integrate.
Web services are most often created using development tools such as Microsoft's Visual Studio.NET or tools from other providers that support Microsoft's .NET or Sun's J2EE Web services runtime environments.
SOAs surround Web services with various technologies-also accessed as services-that are used to manage, orchestrate and choreograph Web services. These SOA services, in effect, add the security, scalability and predictability that enterprises need. These core SOA services include:
1. Services registry. Using the Universal Description, Discovery and Integration (UDDI) standard, services registries are like phone books for Web services. They allow Web services to find one another and provide the information needed for one service to connect and exchange data or transactions with another. Vendors such as Microsoft, Novell, Systinet Corp. and Cape Clear Software Inc. provide this technology.
2. Enterprise services bus. These products provide services for reliably routing messages between Web services and transforming content generated by one Web service so that it can be understood by another. ESB vendors include Fiorano Software Inc.
3. Web services management. These tools give enterprises visibility into how a given Web service is performing and even provide for establishing and monitoring service levels. Providers include Actional Corp. and Digital Evolution Inc.
4. Web services security and identity management. Using standards such as WS-Security and the Security Assertion Markup Language (SAML), these tools keep Web services secure by, among other things, authenticating Web services and their users. Providers include Novell and IBM's Tivoli unit.
5. Web services development and programming tools. Besides tools such as Microsoft's VS.Net, products in this category include tools for exposing legacy system interfaces as Web services, allowing existing applications to communicate with newer applications. Providers include integration broker and enterprise application providers such as BEA and webMethods.