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The term ontological commitment is used as a general term in both philosophy and in information systems to refer to the essential elements of an ontology. An ontological commitment in describing ontological comparisons is taken to refer to a subset of elements of an ontology that it shares with all other ontologies based upon the same theory or conceptualization (see next section for more detail).[3][4] Quine proposed that, given some theory, its ontological commitment could be found by what might be called a translation via techniques of symbolic logic and a search through this translation for statements involving there exists at least one ‘such-and-such’.[5] Such statements are called quantifier expressions and the formulation ‘there exists’ in symbolic logic is represented by the 'turned E' or ∃.[6] A list of the ‘such-and-such’ can then be examined to determine subsets that can serve as minimal sets in terms of which the others can be defined, and any such minimal set is an ontological commitment of the theory. This approach appears to involve only a list of ‘such-and-such’, but of course finding a minimal set of ‘such-and-such’ also involves at least some of the relations specified to hold between them.
This view of ontological commitment leaves considerations of what really is to ontology and focuses upon what amounts to a linguistic analysis. It is more an issue of semantic categories.[7]
In information science, a conceptualization is an abstract simplified view of some selected part of the world, containing the objects, concepts, and other entities that are presumed of interest for some particular purpose and the relationships between them.[8][9]
An ontology provides an explicit specification of a conceptualization, and it may occur that a conceptualization can be realized by several distinct ontologies.[8] "An ontology is language-dependent, while a conceptualization is language-independent."[1] Guarino elaborates on what he means by 'language independent' to say that a conceptualization is always the same, "independently of the language used to describe it".[1] Not all workers in knowledge engineering use the term ‘conceptualization’, but instead refer to the conceptualization itself as an overarching ontology.[10]
As a higher level abstraction, a conceptualization facilitates the discussion and comparison of its various ontologies, facilitating knowledge sharing and reuse.[10] Each ontology based upon the same overarching conceptualization maps the conceptualization into specific elements and their relationships.
The question then arises as to how to describe the 'conceptualization' in terms that can encompass multiple ontologies. This issue has been called the 'Tower of Babel' problem, that is, how can persons used to one ontology talk with others using a different ontology?[9][2] This problem is easily grasped, but a general resolution is not at hand. It can be a 'bottom-up' or a 'top-down' approach, or something in between.[11]
However, in more artificial situations, such as information systems, the idea of a 'conceptualization' and the 'ontological commitment' of various ontologies that realize the 'conceptualization' is possible.[1][12] The formation of a conceptualization and its ontologies involves these steps:[13]
An example of the problems encountered in comparing ontologies is found in translation between human languages. Ostensibly, as all humans live in the same world and have the same physical senses with which to see the world, one might expect to correlate human activity with language and thereby make rules for translation. However, that view is utopian because humans act upon cultural interpretation of their surroundings, and relating two cultures is an entirely different matter than understanding what term in both represents a 'rabbit'.[14][15] Some suggest that humans think in 'mentalese', but so far we don't have access to this level of conceptualization.[16]
However, in more artificial situations, such as information systems, the idea of a 'conceptualization' and 'ontological commitment' to various ontologies that realize the 'conceptualization' is possible.[1][12] A trivial example of moving conception into a language leading to a variety of ontologies is the expression of a process in pseudocode (a strictly structured form of ordinary language) leading to implementation in several different formal computer languages like Lisp or Fortran. The pseudocode makes it easier to understand the instructions and compare implementations, but the formal languages make possible the compilation of the ideas as computer instructions.
Another example is mathematics, where a very general formulation (the analog of a conceptualization) is illustrated with 'applications' that are more specialized examples. For instance, aspects of a function space can be illustrated using a vector space or a topological space that introduce interpretations of the 'elements' of the conceptualization and additional relationships between them but preserve the connections required in the function space.