In this first section of the book, we briefly review the industry standards, technologies and concepts that underlie Web services. These critical technologies support the development of Web services as well as applications that use (or consume) Web services. But, be forewarned that these foundational technologies do not provide everything necessary to build Web services and applications that meet enterprise requirements. We cover these advanced technologies in Section Two of this book.
In this section, we describe the following technologies that together make up the basic Web services platform:
Chapter 2: XML Fundamentals. In this first of three chapters in Part One, we start with a discussion of the fundamentals of the eXtensible Markup Language (XML), the basic technology on which Web services are based. From network protocols up the stack to back-end databases, XML in all its forms has had a commoditizing effect on enterprise computing systems and being both platform and language independent is a natural choice for the level of interoperability required of Web services.
Chapter 3: SOAP and WSDL. Here we describe in detail the two technologies that make up the foundations of Web services: SOAP and WSDL. SOAP (Simple Object Access Protocol) is an XML-based mechanism for exchanging information between applications within a distributed environment. This information exchange mechanism can be used to send messages between applications and, more specifically, can be used to implement remote procedure calls (RPCs). WSDL (Web Services Description Language) is an XML-based language for describing Web services. Through a WSDL description, a client application can determine the location of the remote Web service, the functions it implements, as well as how to access and use each function.
Chapter 4: UDDI. In this chapter, we describe UDDI (Universal Description, Discovery, and Integration), which is a specification for a registry of information for Web services. UDDI defines a means to publish and, more importantly, discover (or search for) information, including WSDL files, about Web services. We also describe the UBR (UDDI Business Registry), which is a global implementation of the UDDI specification.
After reading Section One, you will have a strong understanding of the technologies, standards and concepts underlying Web services. Refer to Section Three for a detailed, step-by-step guide and lots of sample source code to actually develop Web services and client applications.