To better understand the guidelines for building an effective thesaurus, we initially provide explanatory notes on the terms we use in order to describe the recommended steps of building the thesaurus. These are:
Source terms
The terminology of each scientific field, the finite set of general concepts which are used by experts in order to describe their scientific methods, results, tools etc., and which we use as empirical material in order to develop broader terms for them. Source terms are often context dependent. In organizing and building thesauri we regard only source terms which are universals. Instances, being the specific realizations of a general term, such as a placename or a person, are outside the scope of this guideline. They are subject to different methodologies and data structures.
Target terms
The broader terms and top-level concepts which we aim to develop following this guideline. Target terms express types of subjects of attribution i.e. universals whose properties reveal the intensionality (see above) of the source terms which are subsumed under the target terms and should be context independent.
Extension
The extension of a term is defined as the set of items for which it is true. It denotes the reference of a term, the range of its applicability by naming the particular items. So the extension of the term 'cat ' is the set of all the cats in the world; the extension of 'red' is the set of all the red things. However, if we define the terms according to their extension, we would not be able to define something that we do not already know or does not already exist. In order to express the meaning of a term we have to refer to its intensionality.
Intension
Roughly speaking the intension of a term is the sum of its properties, state of affairs, qualities etc. that constitute the necessary and sufficient conditions for being in the extension of a term/concept. In other words, it is the content of a term, its meaning.
For example, the intension of "bachelor" might be something like: adult, unmarried male. Being an adult, being unmarried, and being male are all necessary conditions for being a bachelor, and their conjunction is a sufficient condition.
However, the fact that the necessary and sufficient conditions of many concepts/terms cannot be detected only through the logical or analytical decomposition of their constituents lead us to additionally introduce the term of conventional intension of terms.
Conventional intension
Conventional intension of a concept/term consists of properties, state of affairs etc. which are commonly understood and accepted as denoting items belonging to the same extension. Conventional intensions are not merely the result of an (arbitrary) agreement between subjects. On the contrary, the intersubjective agreement on the conventional intensions is based on their reference to a known reality (Millikan, 2010), which exhibits some distinct forms, than a logical determination. For instance, “Human being” is sufficiently known to us and distinct from other things, even without DNA analysis. For deciding about the criteria upon which we commonly agree to use in order to define the properties of the concepts (intension) with a possible extension, the bottom-up method turned to be a very important methodological tool.
