Composing and decomposing ontologies: a logic-based approach

在计算机科学中，本体被用来为一个领域的兴趣提供一个共同的词汇表，以及对词汇表中术语含义的描述和它们之间的关系，就像在百科全书中一样。从这个意义上说，本体越来越多地用于知识管理系统，医学和生物信息学，并设置在语义Web和网格中发挥关键作用。为了计算机可访问，现代本体是基于描述逻辑（DL）（如OWL）的本体语言来制定的。目前的应用程序正在导致大型和复杂的本体（有时超过30万个不同的术语）的发展。工程和维护这样的本体是一项复杂的任务，它必须小心进行的本体是有用的。它可能涉及一组本体工程师和领域专家合作，以设计本体，更新它以反映领域的变化/发展，并将其与其他本体集成，以覆盖更大的领域。使用基于DL的本体语言（如OWL）有两个优点：（1）它们具有明确的语义，这意味着术语的含义以明确的方式指定，从而实现对本体的共享理解;（2）我们可以利用DL推理机的推理服务进行本体工程和使用。这些服务已经改变了本体工程师的工作方式。然而，这些服务是不够的工程和维护大型本体，特别是在协作的情况下。本体的局部变化以及这些变化之间的交互可能具有当前不可预测的高度非局部影响。只有在修改之后，才能根据所有拟议的修改来审查这些影响。即使这样，也有一些变化的影响是使用当前的推理服务套件无法检测到的。总之，本体工程的状态非常类似于结构化编程技术出现之前的软件工程状态：本体不能被分解成语义上不同的组件，我们不能预测（局部）变化的范围，以及如何重用本体的部分或安全地组合它们是开放的问题。在软件工程中，人工文档和严格的过程限制已经到位，以及结构化程序的初步机制。随着这些机制变得越来越复杂，它们导致了新的自动化技术，用于转换程序以实现性能、理解和重用。有一个令人信服的论点是，方法和算法支持的组成和分解本体在一个可控的方式将是关键，支持协作本体工程和重用。更准确地说，我们计划开发方法和算法支持（T1）开发具有接口的本体（以及对它们的使用的可接受的限制），其保证如果这样的本体与其他本体组合，则它既不破坏也不被与它们组合的本体破坏;（T2）评估可能已经以完全不受限制的方式构建的一组给定本体的组成的结果;（T3）将一个大的本体分解成可以以受控的方式编辑的模块。上面，诸如“以受控的方式”，“损坏的本体”和“后果”之类的术语故意保持相当模糊。实际上，本项目的一个目标是提供上述（T1）-（T3）的严格但实用和有用的正式规范。这方面的研究只是在最近才开始进行，而建议者已经为实际发展作出了一些开创性的贡献。拟议的办法是这一工作路线的延续，即，它是基于逻辑的，并且建立在保守扩展的概念上。

In computer science, ontologies are used to provide a common vocabulary for a domain ofinterest together with descriptions of the meaning of terms built from the vocabulary and relationships between them, like in an encycopedia. Ontologies in this sense are increasingly used in knowledge management systems, medical and bio-informatics and are set to play a key role in the semantic web and grid. In order to be computer-accessible, modern ontologies are formulated in an ontology language based on description logics (DLs) such as OWL. Current applications are leading to the development of large and complex ontologies (sometimes more than 300,000 different terms). Engineering and maintaining such ontologies is a complex task, and it has to be carried out with care for the ontology to be of use. It may involve a group of ontology engineers and domain experts co-operating in order to design the ontology, update it to reflect changes/developments in the domain, and integrate it with other ontologies so as to cover larger domains. Using a DL based ontology language such as OWL has two advantages: (1) they have an unambiguous semantics , which means that the meaning of terms is specified in unambiguous way, thereby enabling shared understanding of an ontology; and (2) we can make use of reasoning services of DL reasoners for ontology engineering and usage. The availability of these services has already changed how ontology engineers work. However, these services are not sufficient for engineering and maintaining large ontologies, especially in the collaborative case. Local changes to an ontology, and interactions between such changes, can have highly non-local effects that are currently unpredictable. The only time to examine these effects is after the changes have been made, in the light of all the proposed changes. And even then there are changes whose impact is not detectable using the current suite of reasoning services. To sum up, the state of ontology engineering is very similar to the state of software engineering before the advent of structured programming techniques: ontologies cannot be decomposed intosemantically distinct components, we cannot predict the scope of a (local) change, and how to re-use parts of ontologies or safely compose them are open problems. In software engineering,human documentation and rigorous process restrictions were put into place, as well as preliminary mechanisms for structuring programs. As these mechanisms have grown more sophisticated, they have led to new automated techniques for transforming programs for performance, understanding, and re-use. It has been convincingly argued that methodologies and algorithmic support for composing anddecomposing ontologies in a controlled way will be the key to supporting collaborative ontology engineering and re-use. More precisely, we plan to develop methodologies and algorithmic support for (T1) developing ontologies with interfaces (and acceptable restrictions on their usage) which guarantee that, if such an ontology is composed with other ontologies, it neither corrupts nor is corrupted by the ontologies they are composed with; (T2) evaluating the consequences of the composition of a set of given ontologies which may have been built in a completely unrestricted way; (T3) decomposing a large ontology into modules that can be edited in a controlled way.Above, terms such as ``in a controlled way'', ``corrupted ontology'', and ``consequence'' are deliberately left rather vague. Indeed, one goal of this project is to provide rigorous but practical and useful formal specifications of (T1)--(T3) above. It is only very recently that research in this direction has been carried out and the proposers have already made some pioneering contributions towards their actual development. The proposed approach is a continuation of this line of work, i.e., it is logic-based and founded on the notion of conservative extensions .