3.1.资源描述框架RDF(简化).ppt

RDF 高春鸣 Introduction XML is a universal metalanguage for defining markup. It provides a uniform framework, and a set of tools like parsers, for interchange of data and metadata between applications. However, XML does not provide any means of talking about the semantics (meaning) of data. For example, there is no intended meaning associated with the nesting of tags; it is up to each application to interpret the nesting. Suppose we want to express the following fact: David Billington is a lecturer of Discrete Mathematics. There are various ways of representing this sentence in XML. Three possibilities are course name=Discrete Mathematics lecturerDavid Billington/lecturer /course lecturer name=David Billington teachesDiscrete Mathematics/teaches /lecturer teachingOffering lecturerDavid Billington/lecturer courseDiscrete Mathematics/course /teachingOffering Note that the first two formalizations include essentially an opposite nesting although they represent the same information. So there is no standard way of assigning meaning to tag nesting. RDF is essentially a data-model.Its basic building block is an object-attribute-value triple,called a statement. XML-based syntax is not a necessary component of the RDF model. RDF is domain-independent in that no assumptions about a particular domain of use are made.It is up to users to define their own terminology in a schema language called RDF Schema (RDFS). XML Schema constrains the structure of XML documents, whereas RDF Schema defines the vocabulary used in RDF data models. In RDFS we can define the vocabulary, specify which properties apply to which kinds of objects and what values they can take, and describe the relationships between objects. RDF思想 RDF基本概念：资源、属性、陈述 资源： a resource as an object, a “thing” we want to talk about。比如Web页面的标题、作者和修改时间，Web文档的版权和许可信息，某个被共享资源的可用计划表等。 属性： a special kind of resources; they describe