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11.5. INTEGRATION

In order to speed up the construction of your ontology, you should consider reuse of definitions already built into other ontologies instead of starting the conceptualization and implementation from scratch. This is why integration is done during the whole life cycle of the ontology. In this activity, we propose the following:

  1. Examine knowledge representation ontologies and meta-ontologies (i.e., in Cyc, in Ontolingua, etc.) to select those that better fit your formalization. If existing meta-ontologies are not appropriate for your ontology, you should start the definition and implementation of a new meta-ontology in a formal language.
  2. Whether or not you reuse existing knowledge representation ontologies and meta-ontologies, the next step is to find which libraries of ontologies provide adequate definitions of terms whose conceptualization is coherent with the terms identified in your conceptualization, foreseeing misinterpretation when they are reused in other ontologies.
  3. Once you have chosen the most appropriate terms, you should check the existence of translators to transform definitions into your target language with as little loss of knowledge as possible.

Sometimes a term in your conceptualization (e.g., centimeter) that should be included in a given ontology (e.g., Standard units) is not provided by the ontology. In this case, you should justify the need to include the missed definitions, as well as the benefits of such inclusion, to the ontology maintainer.

As a result of this phase, METHONTOLOGY proposes the development of an integration document. Summarizing, the meta-ontology you will use and, for each and every term whose definition is going to be used, the name of the term in the conceptual model, the name of the ontology from which you will take its definition, the name of the definition, and its arguments in the ontology, as shown in Table 11.

When we developed the Chemical ontology, we used public Ontolingua ontologies like: KIF-numbers, Standard-Units, Physical-Quantities and EngMath (see http://www-ksl.stanford.edu). For example, the atomic volume units could be defined using the definition of "mole" given by the Standard Unit ontology, and "expt" defined in KIF-numbers.


TABLE 11
An Example of An Integration Document
 
Meta-ontology The frame-ontology in Ontolingua


Term in your conceptualization Ontology to be reused Name of the term in the ontology
 
Mole Standard-Unit in Ontolingua Mole
Centimeter Standard-Unit in Ontolingua Undefined
Exponent KIF-Number in Ontolingua Expt

11.6. IMPLEMENTATION

Ontology implementation requires the use of an environment that supports the knowledge representation ontology, the meta-ontology, and ontologies selected at the integration phase. The result of this phase is the ontology codified in a formal language. Description logic-based languages have their roots in the KL-ONE family: LOOM (MacGregor, 1991) and CLASSIC are the most commonly used. We cite Ontolingua (Farquhar et al., 1995) as the most representative frame-based representation language for building ontologies.

Any ontology development environment should provide, at least: a lexical and syntactic analyzer to ensure the absence of lexical and syntactic errors; translators, to guarantee the portability of the definitions into other target languages; an editor, to add, remove, or modify definitions; a browser, to inspect the library of ontologies and their definitions; a searcher, to look for the most appropriate definitions; evaluators, to detect incompleteness, inconsistencies, and redundant knowledge; an automatic maintainer, to manage the inclusion, removal, or modification of existing definitions, and so on. Below, some of the definitions previously conceptualized above have been codified in Ontonlingua.

Define-Class Alkali (?Alkali)
"Their valence layer electron-structure is ns1. The Alkali 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."
 :def
 (and
  (Non-Transition-Metals ?Alkali)
  (Has-Instance ?Alkali Lithium Sodium Potasium Rubidium Cesium Francium)))

(Define-Class Elements (?Elements)
"It is a substance that is made up only of atoms with the same number of protons."
 :def
 (and
  (Has-One ?Elements Atomic-Number)
  (Has-One ?Elements Atomic-Volume-At-20-Celsius-Degrees)
  (Has-One ?Elements Atomic-Weight)
  (Has-Some ?Elements Boiling-Point)
  (Has-Some ?Elements Crystalline-Structure)
  (Has-One ?Elements Density-At-20-Celsius-Degrees)
  (Has-One ?Elements Electronegativity)
  (Has-One ?Elements Electronic-Affinity)
  (Has-One ?Elements Electronic-Structure)
  (Has-One ?Elements Group)
  (Has-One ?Elements Half-Life)
  (Has-One ?Elements Hardness-Scale)
  (Has-One ?Elements Ionization-Energies)
  (Has-Some ?Elements Melting-Point)
  (Has-One ?Elements Oxidation-State)
  (Has-One ?Elements Period)
  (Has-One ?Elements Radioactivity-Constant)
  (Has-One ?Elements Resistivity-At-20-Celsius-Degrees)
  (Has-One ?Elements Semi-disintegration-Period)
  (Has-One ?Elements Specific-Heat-At-Std-Temperature)
  (Has-One ?Elements Symbol)
:axiom-def
 (Exhaustive-Subclass-Partition Elements
  (Setof Reactiveless
  Reactiveness))

(Define-Class Metals (?Metals)
"They conduct electricity and the heat. They are solids that form very regular and wide nets. They have a low electronegativity."
 :def
 (and
  (Reactiveness ?Metals))
:axiom-def
 (Exhaustive-Subclass-Partition Metals
  (Setof Non-Transition-Metals Transition-Metals))

(Define-Relation Density-At-20-Celsius-Degrees (?Elements ?Density-Quantity)
"Density of a substance is the mass of a volume unit."
 :def
 (and
  (Elements ?Elements)
  (Density-Quantity ?Density-Quantity)
  (>= ?Density-Quantity (/ (* 0 Gram) (expt Centimeter 3)))
  (=< ?Density-Quantity (/ (* 25 Gram) (expt Centimeter 3))))
 :Axiom-Def
  (and
  (Minimum-Slot-Cardinality Density-At-20-Celsius-Degrees 1)
  (Maximum-Slot-Cardinality Density-At-20-Celsius-Degrees 1)))


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