1. XML processing specifications

The role of XML (eXtensible Markup Language) in service programming is not limited to the modeling and representation of data alone. The flexibility of the language and its almost infinite possibilities for extension have rapidly given it an important role in the very modeling of processing. XML has revived a classic method of modeling data processing, the declarative approach, in which processes are themselves considered to be data of a particular type. Thus, several XML dialects have been developed with the idea of specifying forms of data processing that can be combined to form more or less complete applications. Very often, the data required for these same applications is itself represented in XML, which is therefore used at two different levels of the architecture of such systems.