How to Build a Business Rules Engine

However, there is one important design implication that needs to be understood.

Rules that utilize subtypes must always fire after the records that they operate on have

been assigned to their subtypes. For instance, Investor records all have to be classi-

fied as “Individual Investor,” “Corporate Investor,” etc., before business rules that cal-

culate subtype-specific data, such as Individual Investor Gross Tax, can be fired. We

shall return to the need to establish the sequence in which rules fire in later chapters.

Unfortunately, as has been pointed out previously, it is impossible to get the

metadata needed for managing hidden subtypes from any data modeling tool. This

contrasts with metadata about tables and columns, dealt with in earlier chapters. ...