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In information science, an upper ontology (also known as a top-level ontology or foundation ontology) is an ontology (in the sense used in information science) which describes very general concepts that are the same across all knowledge domains. An important function of an upper ontology is to support very broad semantic interoperability between a large number of ontologies which are accessible ranking "under" this upper ontology. As the rank metaphor suggests, it is usually a hierarchy of entities and associated rules (both theorems and regulations) that attempts to describe those general entities that do not belong to a specific problem domain. The seemingly conflicting use of metaphors implying a solid rigorous bottom-up "foundation" or a top-down imposition of somewhat arbitrary, and possibly political, decisions is no accident – the field is characterized by the usual mix of controversy, politics, competing approaches and academic rivalry. Some upper ontologies have led to commercial products, causing a financial incentive to promote one ontology over the competing systems. Debates notwithstanding, it can be said that a very important part of each upper ontology can be considered as the computational implementation of natural philosophy, which itself is a more empirical method for investigating the topics within the philosophical discipline of physical ontology. Library classification systems predate these upper ontology systems. Though library classifications organize and categorize knowledge using general concepts that are the same across all knowledge domains, neither system is a replacement for the other. ==Development== Upper ontologies are also commercially valuable, creating competition to define them. Peter Murray-Rust has claimed that this leads to "semantic and ontological warfare due to competing standards", and accordingly any standard foundation ontology is likely to be contested among commercial or political parties, each with their own idea of "what exists". An important factor exacerbating the failure to arrive at a common approach has been the lack of open-source applications that would permit the testing of different ontologies in the same computational environment. The differences have been debated largely on theoretical grounds, or are merely the result of personal preferences, with no method to objectively compare practical performance. No particular upper ontology has yet gained widespread acceptance as a de facto standard. Different organizations have attempted to define standards for specific domains. The 'Process Specification Language' (PSL) created by the National Institute for Standards and Technology (NIST) is one example. Another important factor leading to the absence of wide adoption of any existing upper ontology is the complexity. An upper ontology typically has from 2,000 to 10,000 elements (classes, relations), with complex interactions among them. The resulting complexity is similar to that of a human natural language, and the learning process can be even longer than for a natural language because of the unfamiliar format and logical rules. The motivation to overcome this learning barrier is largely absent because of the paucity of publicly accessible examples of use. As a result, those building domain ontologies for local applications tend to create the simplest possible domain-specific ontology, not related to any upper ontology. Such domain ontologies may function adequately for the local purpose, but they are very time-consuming to relate accurately to other domain ontologies. There has been debate over whether the concept of using a single, shared upper ontology is even feasible or practical at all. There has been further debate over whether the debates are valid – often leading to outright censorship and boosterism of particular approaches in supposedly neutral sources. Some of these arguments are outlined below. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Upper ontology」の詳細全文を読む スポンサード リンク
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