本体

本体

一、 本体的概念

本体（Ontology ）的概念最初起源于哲学领域，可以追溯到公元前古希腊哲学家亚里士多德（384-322 b.c.）。它在哲学中的定义为"对世界上客观存在物的系统地描述，即存在论"，是客观存在的一个系统的解释或说明，关心的是客观现实的抽象本质。

在人工智能界，最早给出Ontology定义的是Neches等人，他们将Ontology定义为"给出构成相关领域词汇的基本术语和关系，以及利用这些术语和关系构成的规定这些词汇外延的规则的定义"。Neches认为："本体定义了组成主题领域的词汇表的基本术语及其关系，以及结合这些术语和关系来定义词汇表外延的规则。"（"An ontology defines the basic terms and relations comprising the vocabulary of a topic area, as well as the rules for combining terms and relations to define extensions to the vocabulary."）。后来在信息系统、知识系统等领域，越来越多的人研究Ontology，并给出了许多不同的定义。其中最著名并被引用得最为广泛的定义是由Gruber提出的，"本体是概念化的明确的规范说明"，原文参见：

"An ontology is an explicit specification of a conceptualization. The term is borrowed from philosophy, where an Ontology is a systematic account of Existence. For AI systems, what "exists" is that which can be represented. When the knowledge of a domain is represented in a declarative formalism, the set of objects that can be represented is called the universe of discourse. This set of objects, and the describable relationships among them, are reflected in the representational vocabulary with which a knowledge-based program represents knowledge. Thus, in the context of AI, we can describe the ontology of a program by defining a set of representational terms. In such an ontology, definitions associate the names of entities in the universe of discourse ( e.g., classes, relations, functions, or other objects) with human-readable text describing what the names mean, and formal axioms that constrain the interpretation and well-formed use of these terms. Formally, an ontology is the statement of a logical theory."。

和这个定义类似的有N. Guarino and P. Giaretta (1995)"本体是概念化的明确的部分的说明/一种逻辑语言的模型"（"an ontology is an explicit, partial account of a conceptualization/ the intended models of a logical language."）。

W. N. Borst对该定义也进行了引申"本体是共享的概念模型的形式化的规范说明"（"An ontology is a formal specification of a shared conceptualization"）

Fensel对这个定义进行分析后认为Ontology的概念包括四个主要方面：

1. 概念化（conceptualization）：客观世界的现象的抽象模型；

2. 明确（explicit）：概念及它们之间联系都被精确定义；

3. 形式化（formal）：精确的数学描述；

4. 共享（share）：本体中反映的知识是其使用者共同认可的。

原文："an abstract model of a phenomenon termed 'conceptualization',a precise mathematical description hints the word 'formal', the precision of concepts and their relationships clearly defined are expressed by the term 'explicit' and the existence of an agreement between ontology users is hinted by the term 'shared'."

Swartout将本体定义为："本体是一个为描述某个领域而按继承关系组织起来作为一个知识库的骨架的一系列术语"。（"An ontology is a hierarchically structured set of terms for describing a domain that can be used as a skeletal foundation for a knowledge base."）。他的定义强调了本体中术语（terms）的重要性。

Fensel定义"本体是对一个特定领域中重要概念的共享的形式化的描述"。（"An ontology is a common, shared and formal description of important concepts in an specific domain."）。

Noy F.N. 认为"本体是对某个领域中的概念的形式化的明确的表示，每个概念的特性描述了概念的各个方面及其约束的特征和属性。"（"An ontology is a formal explicit representation of concepts in a domain, properties of each concept describes characteristics and attributes of the concept known as slots and constrains on these slots."）。

Fonseca定义"本体是以某一观点用详细明确的词汇表描述实体、概念、特性和相关功能的理论"。（"An ontology is a theory which uses a specific vocabulary to describe entities, classes, properties and related function with certain point of view."）。

Starla认为"本体必需包括所使用术语的规范说明、决定这些术语含义的协议、以及术语之间的联系，来表达概念"。（"An ontology necessarily includes a specification of the terms used (terminology) and agreements that allow to determine their meaning, along with the possible inter-relationships between these terms, standing for "concepts"."）。

M. Uschold and M. Gruninger认为""（"Ontology is an explicit account or representation of (some part of) a conceptualisation."）。他还推荐了一个来自SRKB（Shared Re-usable Knowledge Bases）电子邮件列表的定义"本体是关于共享的概念模型的协议。共享的概念模型包括进行领域知识建模的概念框架、互操作的agent之间进行交流的内容明确协议、以及表达特定领域理论的协定。在知识共享的上下文环境中，本体特指表达性词汇表的定义的形式。一个非常简单的例子就是分类的层次结构，指明了类和它们之间的包含关系。关系数据库模式的作用也和本体一样，它指定了某些共享数据库之间可以存在的关系以及必须保持的完整性约束"（"Ontologies are agreements about shared conceptualization. Shared conceptualizations include conceptual frameworks for modeling domain knowledge; content-specific protocols for communication among inter-operating agents; and agreements about the representation of particular domain theories. In the knowledge sharing context, ontologies are specified in the form of definitions of representational vocabulary. A very simple case would be a type hierarchy, specifying classes and their subsumption relationships. Relational database shemata also serve as ontologies by specifying the relations that can exist in some shared database and the integrity constraints that must hold for them."）。