XML, Related Technologies, and Their Relevance to Web Services We have seen earlier that the Web service agents (requesters and providers) exchange information in the form of messages. These messages are defined in terms of XML Infoset. [2] The importance of XML lies on the concepts of a standard-based, flexible, and extendable data format. The Web service messages are defined using XML Infoset, XML Schema, and XML Namespace standards. Understand that these base concepts of XML messages is important to adhere to in order to develop interoperable solutions. The XML Infoset defines a set of information items and their properties, which describes an XML document. These definitions help the standards and tools to validate the XML documents created. For example, the WSDL standard must conform to the XML Infoset definition of an XML document. This is also valid for the messages exchanged between agents. A well- formed XML message enables interoperation and easier integration. One important concern that may arise is the serialization format of the XML documents for transport and binding. There are many serialization formats available for XML including simple XML text streams to binary XML streams. Note that the wire format of the message is transport and binding dependent. The other notable XML construct is the message schema or message format definition. These schemas can be defined using the XML schema [3] standard, but may not be sufficient for more complex types and assertions. As of today, most of the XML systems tend to use XML schema as the standard for type definition. In the coming years we will witness more evolution in this area with the maturity and intermingling of XML schema with other standards such as RDF, [4] RELAX-NG. [5] We can observe in many implementation situations that the complexities of the XML messages are growing with numerous applications and standards. A proper partitioning of XML documents is needed for the correct description and exchange of the messages. The XML community addresses this document versioning and partitioning problem with XML namespace [6] definitions. As we have seen in the previous illustration, these XML technologies form the basis for all Web services-related standards and messages. This list can be extended to other XML family suites of protocols such as XML Base, [7] XPath, [8] and XPointer. [9] | 