An object has a distinguished identity, a changeable state and
some well-defined behaviour. Similarity between a collection of objects
can be captured in terms of a class
7. a. intr. To state an objection or adverse reason;
now often in weakened sense: To express or feel disapproval, to
2. Something thrown or put in the way, so as to
interrupt or obstruct the course of a person or thing; an obstacle,
a hindrance. [Obsolete].
3. a. Something placed before the eyes, or presented to the
sight or other sense; an individual thing seen or perceived, or that
may be seen or perceived; a material thing ...
b. Something which on being seen excites a particular emotion,
as admiration, horror, disdain, commiseration, amusement ...
4. That to which action, thought, or feeling is directed; the
thing (or person) to which something is done, or upon or about which
something acts or operates
-- Oxford English Dictionary,
Object-oriented programming focuses
on objects that persist and yet change over time.
Since animals persist and yet change, they belong conceptually
at the object-oriented level, and we say that Dog is a
'subclass' of Mammal, and Mammal is a 'subclass' of
Vertebrate. However, since numbers do not change, they
belong at the functional level, and we say that Nat is a
'subsort' of Int, and Int is a 'subsort' of Rat.
Thus both functional and object-oriented levels have an inclusion
relation, respectively expressed as subsort and subclass, with the
class of dogs included in the class of
mammals, and the set of natural numbers included in the set of
integers. Both relations are partial orderings under set-theoretic
-- Goguen & Meseguer.
Functional, Object-Oriented and Relational Programming with
Logical Semantics. 1987
An object has a set of operations and a state that
remembers the effect of the operations. Objects communicate by
sending each other messages to perform operations. Object may be
contrasted to functions, which have no memory. Whereas function
values are completely determined by their arguments, an object may
learn from experience, its reaction to an operation being determined
by its invocation history.
Classification Paradigm. 1987