On the left side one has the more informal Ontologies and on the right site the more formal Ontologies. The Expressivity on the right site is much higher than on the left site. This means on the right site one has the more heavy-weight Ontologies and on the left site one has the light-weight Ontologies.
Usually one starts with a
Controlled Vocabulary, where only specific Terms are allowed and one does not necessary explain what this terms mean. The only Explanation which given might be in Natural Language, but then it is not only a Vocabulary as one has defined the meaning in Sense of an informal Definition then one as a
A Vocabulary is nothing else than a finite List of Terms that might be used, so it is only a kind of Catalog.
If one Explains Terms, then one has a Glossary, which means one has a Term that is allowed to be used and on the other hand one defines what is meant by the Term, what is the Semantics of the Term, but the Definition is only given in an informal way in natural Language.
A Thesaurus is a Glossary with more structure. Thesauri are in Text processing Engines for example. The name comes from Geek and means "Treasure house". This is a Controlled Vocabulary with Concepts that are connected via specific Relations. For example, one has the equivalence Relations which means for a specific Term Synonyms are given, i.e. Terms that mean the same, but are different. Then Hierarchies are given, i.e. what is a subclass and what is a superclass. Here Subconcepts and Superconcepts are given to a specific Term. Homographs are also disambiguated, which means here one has Homonyms, which means the same Term can have in a different Context, a different Semantics which are called Homonyms. On the other hand there can be Association given to similar Concepts. It is more formal than a Glossary as Relations to other Concepts are given.
Taxonomies (Greek tassein =
to arrange and nomos =
method) are definitions hierarchical System of groups. It is also a Classification Schema and a Nomenclature.
One can distinguish different forms of Taxonomies. For example there is the informal IS-A-Hierarchy which is a explicit Hierarchy of Classes, but the Subclasses Relations are not strict, which means that are Subclass might also be Subclass of another Superclass. Therefore it is not a Tree, but it is a Graph where one has more than one path between two nodes between two layers of Hierarchy.
So one puts more Semantic Expressivity on each stage of this Hierarchy.