Semantic Web Services

An Introduction of Semantic Web Services

   What is the  Semantic Web?

    The Semantic Web is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. You can think of it as being an efficient way of representing data on the World Wide Web, or as a globally linked database.

    The Semantic Web was thought up by Tim Berners-Lee, inventor of the WWW, URIs, HTTP, and HTML. There is a dedicated team of people at the World Wide Web consortium (W3C) working to improve, extend and standardize the system, and many languages, publications, tools and so on have already been developed. However, Semantic Web technologies are still very much in their infancies, and although the future of the project in general appears to be bright, there seems to be little consensus about the likely direction and characteristics of the early Semantic Web.

   The main point of Semantic Web

  •  URL(Uniform Resource Identifier) 
    A URI is simply a Web identifier: like the strings starting with "http:" or "ftp:" that you often find on the World Wide Web.
  •  XML(eXtensible  Markup Language)
    XML is a universal meta-language for defining markup. It provides a uniform framework, and a set of tools like parsers, for interchange of data and meta-data between applications.
  •  RDF(Resource Description Framework)
    Although often called a “language”, RDF is essentially a data-model. Its basic building block is an object-attribute-value triple, called a statement. It is up to users to define their own terminology in a schema language called RDF Schema (RDFS).
  •  OWL(Web Ontology Language)
    Ontology languages allow users to write explicit, formal conceptualizations of domain models. OWL is partially mapped on a description logic. An introduction of description logic refers to here.

    What is the Semantic Web Services 

    Semantic Web Service is defined as a “self-contained, self-describing, semantically marked-up software resources that can be published, discovered, composed and executed across the Web in a task driven automatic way.”

The lifecycle of semantic Web processes includes the description/annotation, the advertisement, the discovery, the selection, the composition of Web services that makeup Web processes, and the execution of Web processes. All these stages are significant for the Web process lifecycle and their success. 

Semantics can play an important role in all stages of Web process lifecycle. In Web services domain, semantics can be classified into the following types illustrated in the Figure above.

Functional Semantics: The power of Web services can be realized only when appropriate services are discovered based on the functional requirements. The functional semantic is characterized by their input, output, precondition and effect semantic.

Data Semantics: All the Web services take a set of inputs and produce a set of out-puts. Data semantic is the semantic specified to the data involved in operation.

QoS Semantics: Each ser-vice can have different quality aspect and hence service selection involves locating the service that provides the best quality criteria match. The QoS Semantic describe the non-functional requirement semantic.

Execution Semantics: Execution semantics of a Web service encompasses the ideas of message sequence, conversation pattern of Web service execution, flow of actions, preconditions and effects of Web service invocation, etc.

    Articles about Semantic Web Services

     1. A Brief Introdution of Description Logic

            More coming soon...