英语翻译Property HierarchiesJust as hierarchy for classes can be

英语翻译
Property Hierarchies
Just as hierarchy for classes can be defined,so can properties.
RDF and RDFS Layers
Consider the RDF statement
“Nuclear Physics is taught by Professor Smith.”
The schema for this contains classes and properties shown in Figure 5-5,which
separates the layers of RDF from RDFS.
Let us consider the following classes:“academic staff” and “courses.” If a
course “c” is taught by academic staff “a” then “c” also involves “a.” We can consider
the class “academic staff” having subclasses:professor,associate professor,
and assistant professor designated by subClassOf (see Fig.5-5).
In addition,property hierarchies consider,“its taught by” is a subproperty of
“involves” (see Fig.5-5).
Figure 5-5 shows that the blocks are properties,ellipses in the RDFS layer
represent classes,while ellipses in the RDF layer are instances.The RDFS is
therefore able to express the ingredients:subClassOf,Class,Property,sub-
PropertyOf,Resource,and so on.
Constraints on Properties
The constraints on properties are introduced through “rdfs:domain” and
“rdfs:range.” The property “rdfs:domain” restricts the set of resources that
may have a given property (i.e.,its domain).The “rdfs:range” property restricts
the set of values for a given property (i.e.,its range).The domain and range
force subjects and objects of a property to be a certain type.
Figure 5-6 shows some relationships between modeling primitives in RDFS.
RDF and RDFS Semantics
In order to make the semantics of RDF and RDFS unambiguous and machine
accessible,the formal language of predicate logic can be used to axiomatically
represent RDF and RDFS.Then,automatic reasoning with RDF and RDFS
becomes possible,even though a first-order logic proof system is required.
The inference system supporting the semantic of RDF and RDFS directly uses
the RDF triplets.This inference system consists of rules of the form:
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属性层次结构
类的层次结构可进行定义,属性的层次结构同样也可以.
RDF 和 RDFS 层
请注意下面的 RDF 语句
“Nuclear Physics is taught by Professor Smith.”
该语句的架构中包含类和属性（如图表 5-5 中所示）,从而将 RDF 的层与 RDFS 的层区别开来.
让我们看看下面这两个类：“academic staff”和“courses”.如果 course “c” 由 academic staff “a” 讲授,且“c”同样包含“a”,我们就认为类“academic staff”包含以下子类：由 subClassOf 指定的 professor、associate professor 以及 assistant professor（请参见图表 5-5）.此外,在属性层次结构中,“its taught by”是“involves”的子属性.
在图表 5-5 中,块为属性,RDFS 层中的椭圆形表示类,而 RDF 层中的椭圆形表示实例.因此,RDFS 可表示以下成分：subClassOf、Class、Property、sub- PropertyOf、Resource 等等.
属性约束
属性约束通过“rdfs:domain”和“rdfs:range”引入.属性“rdfs:domain”限制可能具有指定属性（即,该属性的域）的资源集.“rdfs:range” 属性限制指定属性（即,该属性的范围）的值集.域和范围是使属性的主题和对象成为特定类型的重要因素.图表5-6 显示了 RDFS 中建模基元之间的某些关联.
RDF 和 RDFS 语义
为了使 RDF 和 RDFS 的语义更加明确并可由计算机处理,可使用谓词逻辑的正式语言来表示 RDF 和 RDFS.这样,便可以自动对 RDF 和 RDFS 进行推导,即使要求一级逻辑证明系统也是如此.支持 RDF 和RDFS 语义的推理系统直接使用RDF 三联.此推理系统由以下窗体规则组成：