This chapter outlines the history of medical classifications in a general cultural context. Classification is a general phenomenon in science and has an outstanding role in the biomedical sciences. Its general principles started to be developed in ancient times, while domain classifications, particularly medical classifications have been constructed from about the 16th-17th century. We demonstrate with several examples that all classifications reflect an underlying theory. The development of the notion of disease during the 17th-19th century essentially influenced disease classifications. Development of classifications currently used in computerised information systems started before the computer era, but computational aspects reshape essentially the whole picture. A new generation of classifications is expected in biomedicine that depends less on human classification effort but uses the power of automated classifiers and reasoners.
Key Terms in this Chapter
Subsumption: Is a relation between classes, where all individuals belong to one class, belong to another by necessity. E.g. all humans are mammalians by necessity (i.e. it can not be otherwise) therefore mammalians subsume humans.
Categorial Structure: A system, that consist of a number of categories or classes arranged in a hierarchical relation, based on subsupmtion
Coding System: A coding system is a plain list of classes or a categorial structure where all classes assinged by some unique symbol sequence.
Nome nclature: A system of canonic terms used to described entities of a domain. The term also used for coding systems designed to represent as much entites of a domain as possible. Contrary to classifications that aim to represent a limited number of abstract categories within the given domain.
Class: A class or category is the entirety of individual entities that share some common exclusive property. It differs from set in the sense, that the change of the number of individuals belonging to a class does not change the class itself. E.g. ‘human’ is a class. Many people may die or born, but this does not change the class human. While a set of humans e.g. that stay in a room changes as soon as somebody leaves or enters the room.
Poly-Hierarchy: Is hierarchy where at least one entity has two independent superordinates. Independent means here that there is no hierarchical relation among them.
Hierarchy: Hierarchy is a structural feature of systems formed from entities among which a transitive, assymmetric and reflexive relation is defined. If the relation is represneted with the > sign, than transitivity means that If a>b and b>c then a>c, Assymmetric means that, If a>b is true than b>a is flase, Reflexivity means that for all ‘a’ it true that a>a. The assymetric (or directed) relation defines sub- and superordinated entity pairs. The term ‘hierarchy’ is often used also for system of categories arranged into a hiearchy.