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11.3.1. Conceptualization of Concepts For each concepts classification tree generated, you build a Data Dictionary (DD). Each DD identifies and includes all the useful and potentially usable domain concepts, their meanings, attributes, instances, etc. The ontologist should fill in the following fields: Concept Name; Synonyms and Acronyms of the concept name; Instances, which include the instances of the concept; Class Attributes, or relevant properties of the concept that describe the concept itself; Instance Attributes or relevant properties that describe the instances of a concept. Table 2 summarizes some concepts (Alkali, halogens, elements) identified in the domain of chemicals, as well as information about their attributes, instances, etc. To be sure that the DD is good, you should check that: (1) the concept description is concise; (2) all the relevant instance attributes, class attributes and instances in the application domain have been identified; and (3) the instance attributes and class attributes are consistent, that is, they make sense for the concept. A table of an instance attribute provides information about the attribute and about its values at the instance. Indeed for each instance attribute included in the DD Instance attribute field, a table must be created. Each table includes the following fields: Instance attribute name; Value type, referring the class of values with which the attribute could be filled in; Unit of measure, for numerical values; Precision of the numerical value; Range of values, which specifies a list or set of possible values of the attribute; Default value, if they are known and if they make sense for the attribute at the instance; Cardinality, which specifies the number of values of the attribute; Inferred from instance attributes, inferred from class attributes, and Inferred from constants, which include the name of those instance attributes, class attributes, and constants that enable inference of the value of this attribute; Formula, which includes cross-references to the tables of formulas that enable calculation of the numerical value of the attribute (there might be more than one formula); To infer, which contains the name of those instance attributes whose values could be inferred using the instance attribute; and References. Tables 3, 4, and 5 show definitions of the instance attributes: "Atomic-Volume-At-20-Celsius-Degrees," "Atomic-Weight," and "Density-At-20-Celsius-Degrees."
Tables of class attributes describe the concept itself, not its instances. For each concept included at the field, a table of class attributes must be created that specify the following fields: Class attribute name; Relation attribute name, which is the name of the attribute that participates in the relationship; Logical relationship, attaches two concepts across logic operators; Value of the class attribute; Unit of measure for numerical values; To infer, which contains the name of those instance attributes whose values could be inferred using the value of the class attributes; and References. Table 6 shows the definitions of the class attributes attached to the concept Halogens. Constants are used to specify information related to the domain of knowledge that always take the same value. They are usually used in formulas: for example, gravitational acceleration is 9.8. Some constants in the domain of chemicals appear in Table 7. For each concepts classification tree, the ontologist should identify a set of constants in a table of constants and describe them as follows: Constant name; Description, which contains the meaning of the constant name; Value of the constant; Unit of measure for numerical values; To infer, with the name of the instance attributes whose values could be inferred using the value of the constant; and References. If the ontologist is sure that all the instances mentioned at the Instance field of the DD exist in the domain, the next step is to create a table of instances for each instance identified in the DD. The fields to fill in are: Instance name; Attributes to be filled in the instance; and Values of these attributes. Check for consistency between attributes and their values. Table 8 is an example of a table of instances.
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