付费电表系统的通用功能和应用过程参考模型（中）
1.2 参考模型的结构 Composition of the reference model
The multitude of functions in a payment metering system can be grouped and then abstracted into generic functions as depicted in Figure 3. This abstract function model is thus a generic representation of the functions in a payment metering system, from which all instances of
specific systems are derived. Each generic function is allocated a class number (1 to 17),
according to which all sub-functions are further classified, each sub-function thus inheriting(继承)
its class from its generic parent function. Functions of class 1 to 11 are the business functions,
while class 12 to 17 are support functions. A business function is one that implements
application-specific business-related logic, while a support function is one that enhances the
functionality of the business functions and also that of other support functions. It can thus be
seen that one business function has a very sp