The inference mechanism of the system is provided by a number of rule classes built into the Rulesystem. To make the reasoning more efficient, the rules are grouped into classes. Depending on the type of knowledge entered, a certain rule class is triggered and new facts are added to the knowledge base. Among these rules, some can be regarded as defaults, i.e., rules for default reasoning. Using these rules it is possible to derive conclusions despite the absence of total information.
Rules is triggered whenever a new item is created.
It contains rules that deduce the sale price and type of each item, viz., whether it is real estate, service, or movable. These rules are defaults and are activated if the user does not provide total information. When an item is created, its owner and kind should be specified. If the sale price of bread is not specified, then it is a couple of dollars. If the sale price of a car is not specified, then ask the user.