Model organization must be efficient to simplify the real world.
In the past few years, varied models have been developed and
integrated with GIS to solve difficult problems. Valuable
models have been put in practice as environment quality
evaluation, resource allocation, etc.. Models can also be used to
agriculture resource planning, soil erosion, and plant growing.
Three ways are put in use: database expression (DE), logical
expression (LE) and program-based expression (PE), with each
has its advantages and disadvantages. The basic principle to
decide which way should be used depends on the to be solved
problem feature. Generally speaking, if the problem needs
continuous numerical calculation, DE will be adopted. In the
other hand if the problem is discrete numerical calculation or
logic judgment, LE is better and more suitable to realize
complex reasoning. In this sense LE will integrates numerical
calculation and logic judgment. In this study both DE and LE
methods are used to cooperate and database is used to store
them, as models can be easily maintained in this way.
In the process of models construction through database,
grammar and implication should be defined first. Grammar and
implication bridge the communication channels for model
constructor and user. This model structure can express complex
mathematical functions like this: