“ ... is a simple, very flexible text format derived from SGML (ISO 8879). Originally designed to meet the challenges of large-scale electronic publishing, XML is also playing an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere. ”
is not a solution but a tool to build solutions
is not a language but a meta-language that require interoperating applications that use it to adopt clear conventions on how to use it
is a standardized text format that is used to represent structured information
e X tensible M arkup L anguage
SGML, XML and their applications HyTime HTML XHTML SMIL SOAP WML SGML XML Meta-Markup Language Markup Language Application
“ A Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP -messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards” . Web Services Glossary, W3C, http://www.w3.org/TR/ws-gloss/
UDDI: Universal Description, Discovery and Integration
“ The Web was designed as an information space, with the goal that it should be useful not only for human-human communication, but also that machines would be able to participate and help. One of the major obstacles to this has been the fact that most information on the Web is designed for human consumption , and even if it was derived from a database with well defined meanings (in at least some terms) for its columns, that the structure of the data is not evident to a robot browsing the web. Leaving aside the artificial intelligence problem of training machines to behave like people, the Semantic Web approach instead develops languages for expressing information in a machine processable form ” .
"If HTML and the Web made all the online documents look like one huge book , RDF, schema, and inference languages will make all the data in the world look like one huge database "
RDF ( R esource D escription F ramework): simple data model to describe resources and their relationships
RDF Schema: is a language for declaring basic class and types for describing the terms used in RDF, that allows defining class hierarchies
SPARQL : S PARQL P rotocol and R DF Q uery L anguage
OWL : W eb O ntology L anguage . Allows enriching the description of properties and classes, including, among others, class disjunction, association cardinality, richer data types, property features (eg. symmetry), etc.