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propagation mechanism on the real domain and domain propagation mechanism
in the definite domain.
2. Bertrand
Bertrand is an advanced constraint language developed by Leler, whose
computational model is a system based on enhanced term rewriting. On the
whole, Bertrand adds the assignment function and type mechanism based on
term rewriting system, which makes Bertrand can solve linear equation about real
number and rational number. Bertrand also includes the function of abstracting
data type. It has been already used for solving some problems in graphics and
circuit.
Bertrand still cannot be regarded as real constraint language, but a generating
tool for constraint satisfaction system. Basically it offers nothing mechanism to
solve dispersed constraint and it doesn't offer propagation mechanism for
interval propagation and order relation on real number domain. Bertrand can only
offer value propagation.
3. Constraint logic programming language¾CHIP
Main research on constraint language concentrates on constraint logic
programming language, which aims to combine constraint satisfaction
technology and logic programming. Such languages introduce constraint
propagation (mainly arc consistency technology) on the basis of Prolog in order
to improve search efficiency and strengthen expressing ability. CHIP(Constraint
handling in Prolog) is such constraint logic programming language with great
influence. The goal of CHIP is to solve a major kind of composition problems
simply, conveniently, flexibly and effectively. CHIP strengthens the ability of
logic programming through offering several kinds of new computational domain:
definite domain, Boolean item and rational item. For all computational domain,
CHIP offers effective constraint solving technology, including consistency
technology of definite domain, unified technology for Boolean domain and pure
type for rational domain and a general delay computing technology.
CHIP is mainly applied to two fields: operations research and hardware
design. However, CHIP lacks the type mechanism which is extremely important
for expressing the domain concept.
4. Constraint Hierarchy and HCLP
“Soft constraint” solving problem is a very interesting and important practical
problem. In this research, the most influential work is from Borning et al.
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