tailieunhanh - Semantic Web Technologies phần 5

người ta có thể sử dụng Web để thu thập các tài liệu trên được xác định trước chủ đề. Khám phá kiến thức, phương pháp tiếp cận đối phó với thu thập tài liệu dựa trên các dữ liệu web được giới thiệu trong các tài liệu theo tên tập trung | 118 ONTOLOGIES FOR KNOWLEDGE MANAGEMENT over information Thus they can be used for indexing querying and reference purposes over nonontological datasets and systems such as databases document and catalog management systems. Because ontological languages have a formal semantics ontologies allow a wider interpretation of data that is inference of facts which are not explicitly stated. In this way they can improve the interoperability and the efficiency of the usage of arbitrary datasets. Ontologies are typically classified depending on the generality of the conceptualization behind them their coverage and intended purpose Upper-level ontologies represent a general model of the world suitable for large variety of tasks domains and application areas. Domain ontologies represent a conceptualization of a specific domain for example road-construction or medicine. Application and task ontologies are such suitable for specific ranges of applications and tasks. An example of such is the PROTON KM module see Subsection . A more extensive overview of the different sorts of ontologies and their usage can be found in Guarino 1998b which also provides discussion on the different ways in which ontology is used as a term and its relation to knowledge bases. Knowledge Base KB is a term with a wide usage and multiple meanings. Here we consider a KB as a dataset with some formal semantics. A KB similarly to an ontology is represented with respect to a knowledge representation formalism which allows automatic inference. It could include multiple axioms definitions rules facts statements and any other primitives. In contrast to ontologies KBs are not intended to represent a shared consensual schema a basic theory or a conceptualization of a domain. Thus ontologies are a specific sort of knowledge base. An ontology can be characterized as comprising a 4-tuple 4 O C R I A Where C is a set of classes representing concepts we wish to reason about in the given domain .