(摘录)(ASWP chap3)Describing Web Resource in RDF

3.1 Introduction

1. RDF schema is quite different from XML Schema

XML Schema constrains the structure of XML documents, whereas RDF Schema defines the vocabulary used in RDF data models.

3.2 RDF: Basic Ideas

1. Concepts

Resource

Property

Statement

2. reification(具体化) mechanism

3. typed literal

RDF里用到的很多数据类型是在XML Schema里定义的，比如Boolean, integer等

3.3 RDF: XML-Based syntax

1.  XML和RDF中Namespace的区别

XML中的namespace是用来保证元素的唯一性.

RDF中的external namespace指向一个RDF文件,这个文件里定义了一些resource,被导入到了当前RDF中.

2. 引用namespace的一种写法

<rdf:RDF

       xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

       xmlns:xsd="http://www.w3.org/2001/XLMSchema#"

       xmlns:uni="http://www.mydomain.org/uni-ns#">

       ……

<rdf:Description rdf:about="CIT1111">

<rdf:type rdf:resource="&uni;course"/>

// 应该相当于 <rdf:type rdf:resource=”http://www.mydomain.org/uni-ns#course”>, 即&uni用来指代xmlns:uni的值

       <uni:courseName>Discrete Mathematics</uni:courseName>

       <uni:isTaughtBy rdf:resource="949318"/>

</rdf:Description>

3.4 RDF Schema: Basic Idea

1. RDF Schema is a primitive ontology language.

2. In RDFS, properties are defined globally.

3. In RDFS, properties also have class hierarchy.

4. RDFS ingredients: subClassOf, Class, Property, subPropertyOf, Resource, etc.

3.5 RDF Schema: The Language

1. Core Class

rdfs:Resource

rdfs:Class

rdfs:Literal

rdf:Property

rdf:Statement

2. Core Property for defining relationship

rdfs:domain

       指定可以做这个property的subjet

rdfs:range

       指定可以做这个property的object

3. Useful Properties for Reification

rdf:subject

rdf:predicate

rdf:object

4. Container Class

rdf:Bag

rdf:Alt

rdf:Seq

5. Utillity Properties

rdfs:seealso

rdfs:comment

3.6 RDF and RDF Schema in RDF Schema

3.7 An Axiomatic Semantics for RDF and RDF Schema

// 没看

逻辑推理

3.8 A Direct Inference System for RDF and RDFS

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3.9 Querying in RQL

1. Why not use XML query language?

(1) 相同的内容可以用不同的形式来表示,无法用统一的XPath语句来查询

如以下3段都表示了相同的意思:

<rdf:Description rdf:about="949318">

       <rdf:type rdf:resource="&uni;lecturer"/>

       <uni:name>David Billington</uni:name>

       <uni:title>Associate Professor</uni:title>

</rdf:Description>

rdf query: /rdf:Description[rdf:type="http://www.mydomain.org/uni-ns#lecturer"]/uni:title

或

<uni:lecturer rdf:about="949318">

       <uni:name>David Billington</uni:name>

       <uni:title>Associate Professor</uni:title>

</uni:lecturer>

rdf query: //uni:lecturer/uni:title

或         

<uni:lecturer rdf:about="949318"

              uni:name="David Billington"

              uni:title="Associate Professor"/>

rdf query: //uni:lecturer/@uni:title

(2) XML 查询语言(如XPath) 不支持semantic(如无法”理解”继承关系)

2 RQL的基本语法

见教材

3.10 Summary

Suggested Reading

An extensive list of tools and other resources is maintained at:

• <http://www.ilrt.bris.ac.uk/discovery/rdf/resources/>.

• <http://www.w3.org/RDF>