From Knowledge Representation:Logical, philosophical and Computational Foundations
Preface
By John F. Sowa

Socrates said he was the midwife of his listners, i.e, he made them reflect more better concerning that which they already knew and become better conscious of it. If we knew what we know , namely, in the use of certain words and concepts that are so subtle in application, we would be astonished at the treasures contained in our knowledge. __IMMANUEL KANT. "Vienna Logic"

苏格拉底曾说，对于听众，他就像助产士，引导听众们反思自己所知，认识自己所知；如果我们明白自己所知道的一切，知道精妙地使用特定的词汇和概念，就会对我们的知识中包含的宝藏感到无比惊讶！__康德《维也纳逻辑》

说明性语言（Declarative Language ）：说明性语言是一种跨平台语言，用于以简洁、易懂表达方式定义基本数据结构（如类型数据的列表、映射、树等）。参考：http://www.ikayzo.org/confluence/display/SDL/Home
The Simple Declarative Language is a cross-platform language used for defining basic data structures such as lists, maps, and trees of typed data in a compact, easy to read representation. A simple API allows one to read, write and access all the data structures using a single class. For property files, configuration files, logs and simple serialization requirements, SDL is designed to be an alternative to XML and properties files. Implementations are available for Java and .NET with more languages on the way.

知识表示是一门多学科交叉的学科（multidisciplinary subject）,其主要理论和技术来自于三个领域：
逻辑（Logic）：提供形式化的结构和推理规则；
本体(Ontology)：定义领域中的各种事物；
计算(Computation)：支持应用，把知识表达和纯哲学加以区分。
没有逻辑，就无法判断陈述是否多余或矛盾；没有本体，术语和符号就无法定义，就会混淆，混乱；没有计算模型，就无法在程序中实现逻辑和本体。
知识表达就是基于领域，将逻辑和本体应用于构建计算模型。

本体定义事物的类别，其表达方式包括：谓词逻辑的谓词、框架的槽、数据库的表、面向对象系统的类等。
Ontology defines categories of things that are expressed in the predicates of predicate logic, the slots in frames, the tables of a database and the classes of an object-oriented system.