relation between kinds of things that relates two concepts whereby the subtype concept is a more specific concept than the supertype concept and has all the aspects that define the supertype concept
|R1 role player: concept||R2 role player: concept|
|R1 role: subtype||R2 role: supertype|
|R1-R2 expression:||is a specialization of|
is a kind of
is a subtype of
|R2-R1 expression:||is a generalization of|
has as subtype
is a supertype of
Note 1 to entry: The constraints by which a supertype concept is defined are also applicable for its subtype concepts. A subtype concept is distinguished from its supertype and its neighbouring subtype concepts by being defined by additional constraints. A concept may be a subtype of more than one supertype concept. An aspect (value) by which a supertype concept is defined is also an aspect of all of its subtype concepts (the aspects are ‘inherited’).
The aspects of a concept shall also be applicable for the individual things that are classified by the kind. An individual thing that is classified by a concept (thus satisfying its defining constraints), is implicitly also classified by the supertypes of the concept. Knowledge about options for a concept is also knowledge about its subtypes, unless the knowledge is further constrained by the definition of the subtype.
The phrase ‘is a specialization of’ has as synonyms ‘is a kind of’ and ’is a subtype of’. The inverse phrase ‘is a generalization of’ has as synonyms ‘has as subtype’ and ‘is a supertype of’.
Thus, the expression A is a kind of B, means that the concept A is a subtype of the concept B. For example, kinds of aspects ( = subtypes of aspects) are: length, width, temperature, colour, etc.
Note 2 to entry: The term that denotes the subtype has a role as hyponym. The term that denotes the supertype has a role as hypernym. EXAMPLE: Assume that ‘means of transport’ is defined as a physical object that is intended to carry load. Furthermore, it is specified that concepts with the names ‘car’ and ‘ship’ are both a specialization of ‘means of transport’. Then this implies that car as well as ship are intended to carry load (without the need to explicitly specify those facts.) Furthermore, assume that individual object #12 is classified as a ‘car’ then the specialization relation implies that object #12 is also a ‘means of transport’.
The concept ‘width’ is a specialization of ‘distance’. If for distance it holds that it can be quantified on a length scale, then that implies that width inherits from distance that it also can be quantified on a length scale.
|car||is a specialization of||means of transport|
|means of transport||is a generalization of||car|
|ship||is a specialization of||means of transport|
Note 3 to entry: The first two examples above are different expressions of the same fact. 
1 Online Browsing Platform (OBP) [WWW Document], n.d. URL https://www.iso.org/obp/ui#search (accessed 4.10.21).