The most fundamental scheme uses attribute-value pairs as seen in the rules for identifying birds. When a system is reasoning about multiple objects, it is necessary to include the object as well as the attribute-value. For example the furniture placement system might be dealing with multiple chairs with different attributes, such as size. The data representation in this case must include the object. Once there are objects in the system, they each might have multiple attributes.
Frames are a more complex way of storing objects and their attribute-values.
Frames add intelligence to the data representation, and allow objects to inherit values from other objects. In a furniture placement system each piece of furniture can inherit default values for length. When the piece is placed, demons are activated which automatically adjust the available space where the item was placed. The acceptability of an expert system depends to a great extent on the quality of the user interface. The easiest to implement interfaces communicate with the user through a scrolling dialog as illustrated in figure 1.4.