Fact sets define the initial pieces of knowledge or data in your expert system. Facts sets are a collection of facts which are automatically asserted every time the inference engine is reset. The facts define the initial state of the world of your expert system, i.e., the people in it, the objects in it, etc. See Facts for more information about facts. Defining a fact set does NOT automatically assert the facts onto the fact base, only when the inference engine is reset do the facts get asserted.
Before creating facts sets, you should define the fact templates, or types, for your facts sets. Fact Sets and facts may be created before defining fact templates, but then the facts will consist only of the relation name and one slot that contains everything else. For example, if you assert '(person tom brown)', this defines a person fact which has a slot that contains the field 'tom brown' (a list of values).
See the Fact Set definition for the syntax of a fact set.