Keystone of our research on concepts’ analysis is the fundamental philosophical position that each concept has a purpose or utility. In building thesauri this utility is specified as the ability to deduce from recognizing an item as instance of a concept potential properties of the same item.

In designing and building thesauri we take into account the following rules and preconditions:

  1. The definitions of the target terms should be based on the intension of the concepts/terms and not on their extension.
    Example: if we define “human” as “driver” i.e. by his incidental property to drive a car, then all people who do not drive are not human!

  2. In defining the target terms, both the semantic and syntactic ambiguity and vagueness should be avoided. In other words, an expert should be able to decide if some item of his discourse is an instance of the term or not. The items for which such a decision cannot be made should be marginal.
    In building and designing thesauri we often encounter two kinds of ambiguity and vagueness:
    • ambiguity related to the substance of a target term (broader categories-top level concepts): the meaning of a target term could be so broad and relative that it could comprise any kind of items without any semantic contiguity or relation.
      Exaple: what is not a “research object”?
      In that case we have to define the broader categories by attributing properties which enable the identification of items not belonging to those categories.   
    • ambiguity related to the polysemy of a term: a term could have multiple, incoherent meanings related to the semantic field (context) they refer to.
      Example:  Mercury could mean: a metal, a planet, a God in mythology.
      Therefore, before classifying the term we have to define the functional restrictions of the thesaurus (below, step 1), in other words, to clarify the context in which we find the term in order to disambiguate it.
       
  3. The definitions of the target terms should allow us to identify the common meaning and not the boundaries between the source terms.
    Example: If we define “armed conflicts” as mutually excluding “peaceful conflicts”, we cannot generalize over all the stages in between, and conflicts which evolve into violence.

  4. The definitions of the target terms we build in order to subsume the source terms should not be, as much as possible, limited to or dependent on a specific context of use.
    Example: X-Ray systems are used by many disciplines, such as medicine, material assaying, art conservation, archaeology. Classifying them as “medical instruments” or “archaeological instruments” would not render anything about their nature. In contrast, they are “instruments for structure analysis of solid things” by substance, rather than by accidental use.

  5. A term may be subsumed under multiple broader categories.
    Example: “carmine” is a “natural dye” and “red colorant”  

  6. The arrangement of the top level concepts of thesauri and also any expansion of them, either horizontally (through the addition of new top-level concepts) or vertically (through the specialization of the existing ones), must follow the principle of exclusion of contradictions (clash-free expansion of the thesaurus).
    Below are some of the examples that show kinds of contradictions we encountered in the environment of controlled vocabularies:
    • terms are defined through self-contradictory properties.
      Example: “Confrontations, conflicts”: “This term comprises complex intentional activities (a combination of activities) that presuppose at least two actors or groups of actors, who understand their interests and demands as competitive and thus aim at their satisfaction through their involvement in situations of controversy”  resulting from natural phenomena.
      Here, the contradiction lies in the fact that we define the term both as the intentional actions carried out by at least two actors and at the same time as situations resulting from natural phenomena.
    • a broader term A is subsumed under a narrower B, which implies that the narrower term B has less properties than the broader term A. In this case the contradiction lies in the inconsistency with the IsA relationship which is the basis for building hierarchies and requires that subsumed terms (narrower terms) have at least all properties of the subsuming one (the broader term) (see below)
      Example: broader term: Stelae (it is a concrete piece of stone bearing inscriptions that can be transferred), narrower term: mobile objects (it comprises objects that can be transferred).
      Here the contradiction lies in the fact that, the narrower term (mobile objects) does not necessarily inherit all the properties of the broader (Stelea). 
    • a narrower term is attributed properties of which, at least one excludes the necessary properties attributed to its broader term.
      Example: broader term: Immobile objects (it comprises objects that cannot be transferred), narrower term: Stelae (it is an object that can be transferred).
      Here the contradiction lies in the fact that “Stelae” seems to posses contradictory properties: it can and cannot be transferred!  

  7. The subsumption of narrower under broader terms should be formulated as an inference supporting the inheritance of the properties of potential instances of the broader term to all the instances of the narrower terms (IsA relationship).  Otherwise, we fall into the kind of contradiction mentioned above (6b).
    Εxample: if we define the broader term: “confrontations, conflicts” as: “complex activities (a combination of activities) that presuppose at least two actors or groups of actors, who understand their interests and demands as competitive and thus aim at their satisfaction through their involvement in situations of controversy”, then, each of its narrower terms ( coups d’etat, legal actions, wars, revolutions, strikes), must inherit the above mentioned properties of the broader term.