# domain theory

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## domain theory

[dō′mān ‚thē·ə·rē]
(solid-state physics)
A theory of the behavior of ferromagnetic and ferroelectric crystals according to which changes in the bulk magnetization and polarization arise from changes in size and orientation of domains that are each polarized to saturation but which point in different directions.

## domain theory

(theory)
A branch of mathematics introduced by Dana Scott in 1970 as a mathematical theory of programming languages, and for nearly a quarter of a century developed almost exclusively in connection with denotational semantics in computer science.

In denotational semantics of programming languages, the meaning of a program is taken to be an element of a domain. A domain is a mathematical structure consisting of a set of values (or "points") and an ordering relation, <= on those values. Domain theory is the study of such structures.

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Different domains correspond to the different types of object with which a program deals. In a language containing functions, we might have a domain X -> Y which is the set of functions from domain X to domain Y with the ordering f <= g iff for all x in X, f x <= g x. In the pure lambda-calculus all objects are functions or applications of functions to other functions. To represent the meaning of such programs, we must solve the recursive equation over domains,

D = D -> D

which states that domain D is (isomorphic to) some function space from D to itself. I.e. it is a fixed point D = F(D) for some operator F that takes a domain D to D -> D. The equivalent equation has no non-trivial solution in set theory.

There are many definitions of domains, with different properties and suitable for different purposes. One commonly used definition is that of Scott domains, often simply called domains, which are omega-algebraic, consistently complete CPOs.

There are domain-theoretic computational models in other branches of mathematics including dynamical systems, fractals, measure theory, integration theory, probability theory, and stochastic processes.

References in periodicals archive ?
If the aforementioned cases from DOD's Encyclopedia of Ethical Failure were viewed through the lens of domain theory, they would fall within the conventional domain.
Where rules may come and go within the conventional domain, the rules in the personal and moral domains are few and enduring, giving a sense of permanence to this part of domain theory.
This being the case, the learning system must not revise its domain theory prematurely since there may not, in fact, be any errors in its theory.
A truth maintenance system (TMS) [28] may be used to maintain the network of concepts that form a domain theory.

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