Some observations on types

TMRA 2009, November 12, LeipzigLars Marius Garshol, <larsga@bouvet.no>

Types in IT

• Types are extremely fundamental– datatypes in programming languages,– classes in OOP,– entities/packages/clusters/structs/records pre-

OOP– entity types in ER and EXPRESS,– classes in UML,– classes in RDF,– topic types in Topic Maps,– ...

Types in language

• Consider what nouns really are– specifically, common nouns

• Aren’t most of them topic types?– car– pencil– country– person– computer– ...

Types in language (2)

• What characterizes types is that they have instances

• You can recognize potential types using a simple “language game”– for a potential type y, if there is an x such that

you can say “x is a y”, y is a type– if you cannot, it is not a type

• Examples– Germany is a country– ___ is an electromagnetic force

Class hierarchies

• Consider how we talk about concepts in everyday conversations– Child: “What is an ozelot?”– Grown-up: “It’s an animal.”– Child: “Oh. What kind of animal?”– Grown-up: “It’s a kind of cat.”

Conclusion

• Types are fundamental in IT because they are fundamental to how we think and speak

• Likewise class hierarchies