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11.2. KNOWLEDGE ACQUISITION

It is important to bear in mind that knowledge acquisition is an independent phase in the ontology development process. However, it is coincident with other phases. As stated previously, most of the acquisition is done simultaneously with the requirements specification phase, and decreases as the ontology development process moves forward.

Experts, books, handbooks, figures, tables, and even other ontologies are sources of knowledge from which the knowledge can be elicited, and acquired, and used in conjunction with techniques such as: brainstorming, interviews, questionnaires, formal and informal texts analysis, knowledge acquisition tools, etc. For example, if you have no clear idea of the purpose of your ontology, the brainstorming technique, informal interviews with experts, and examination of similar ontologies will allow you to elaborate a preliminary glossary with terms that are potentially relevant. To refine the list of terms and their meanings, formal and informal texts, analysis techniques in books and handbooks, combined with structured and nonstructured interviews with experts might be used to include or remove terms in the glossary. Interviews with experts might help you build concepts classification trees and compare them with figures given in books.

11.3. CONCEPTUALIZATION

In this phase, METHONTOLOGY proposes to structure the domain knowledge in a conceptual model (a noncomputable representation of the world) that describes the domain in terms of the domain vocabulary identified in the ontology specification phase. The first thing to do is to build a complete Glossary of Terms (GT) as shown in Table 1. Terms include concepts, instances, verbs, and properties. So, the GT identifies and gathers all the useful and potentially usable domain knowledge and its meanings. Note that you do not start from scratch when you develop your GT. If you have drawn up a good requirements specification document, many terms will have been identified in that document. Others will be identified as the ontology construction process advances. Then, these new terms must be included in the GT.

Once you have almost completed the GT, you need to group terms as concepts and verbs. Each set of concepts/verbs would include concepts/verbs that are closely related to other concepts/verbs inside the same group as opposed to other groups. Indeed, for each set of related concepts and related verbs, a concepts classification tree and a verbs diagram is built. Figures 9 and 10 show a concepts classification tree and a verbs diagram, respectively, in the domain of chemicals. After they have been built, you can split your ontology development process into different, but related, development teams. Figure 11 graphically summarizes the intermediate representations used in the conceptualization phase.


TABLE 1
Glossary of Terms
 
Name Description
 
Alkali Their valence layer electron structure is ns1. The alkalis are soft; when they are cut, they have a silvery-white color. When they are exposed to air, they cloud because of oxidation. Therefore, they are kept in an inert atmosphere or submerged in mineral oil. The melting point, the boiling point, and the specific heat decrease as the atomic number increases. They react with the hydrogen.
Halogens They have seven electrons at the valence layer, two of which are in an s orbit and other in a p orbit. They easily react because they only need one electron to obtain eight in their valence layer. Their melting point, boiling point, and density increase with the atomic number.
Element It is a substance that is made up only of atoms with the same number of protons.
Atomic-Volume-At-20-Celsius-Degrees It is the volume occupied by 1 Gram-Atom of a element at 20°C. The gram atom is the mass equal to atomic weight expressed in grams.
Atomic-Weight The atomic weight is the relative mass of an atom of an element on a scale in the which is taken as a unit the twelfth part of the carbon 12 isotope.
Density-At-20-Celsius-Degrees Density of a substance is the mass of a volume unit.
Chlorine It is member of the halogen (salt-forming) group of elements; it is a greenish-yellow gas, combining with nearly all elements. Chlorine is widely used in making many everyday products. It is used for producing safe drinking water the world over. Even the smallest water supplies are now usually chlorinated. It is also extensively used in the production of paper products, dyestuffs, textiles, petroleum products, medicines, antiseptics, insecticides, foodstuffs, solvents, paints, plastics, and many other consumer goods. Most of the chlorine produced is used in the manufacture of chlorinated compounds, etc.


FIGURE 9 Concepts classification tree in the domain of chemicals.


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