Technologies

SOA relies on one of the unifying ideas in modern data processing: Extensible Markup Language (XML), a set of widely accepted rules for organizing data in a text format. We provide an overview of XML and include details that will deepen your understanding of the following technologies, all covered in this book:

• Web Services Description Language (WSDL): WSDL is an XML-based format for describing how to access a Web service, which is a service that itself uses XML for data exchange. Increasingly, WSDL is used to describe services of any kind.

• SOAP (which stands for … SOAP, though it was once called Simple Object Access Protocol): SOAP is the most widely used format for transmitting data to and from a Web service.

• XML Path Language (XPath): XPath is a language used to derive data from XML source such as SOAP data. The language is useful for working with a variety of technologies, including several described in this book. We offer a tutorial introduction. The material is probably sufficient for your work in XPath 1.0 and is intended to make your investigation of XPath 2.0 far easier.

• Business Process Execution Language (BPEL): BPEL 2.0 is a language that coordinates services and whose preceding version is already in numerous products. We give you a comprehensive description of BPEL 2.0, including a quick-reference guide.

• Service Component Architecture (SCA): SCA is a proposed standard for composing and deploying SOA software that can include but is not limited to Web services. SCA is slated to become the basis of commercial products from several vendors in 2007.

• Service Data Objects (SDO): SDO is a proposed standard for representing data in a single way, even if the data comes from different types of data sources. SDO is likely to accompany SCA into the limelight.

• WS-*: This abbreviation (sometimes called WS splat) refers to a group of Web-services specifications being developed to handle runtime quality-of-service issues such as reliability (is the transmitted data guaranteed to arrive?); security (will the data be protected from unauthorized viewing and change?); and transaction control (will the data be saved only after a business interaction is complete?). We give a brief and clear description of more than a dozen of these specifications.