This was a presentation by an IBMer who works in AI systems development. He was knowledgeable and had a varied background in military systems and the academic world. He also had it in for the IRS for some reason; he mentioned several times that what the world needed was an expert system written for the tax code. In fact, he said that Congress should mandate that an expert system be written each time there is a change to the tax law. "That way, we would avoid conflicting tax laws and other b___s___ that follows" he said to my substantial amazement.

I've talked about rule-based expert systems before: they're composed of IF-THEN rules that fire independently of each other. In frame systems, you represent each object you are modeling in a data structure called a frame. Frames are roughly analogous to records in a database. Records contain fields; frames contain "slots". In a record, each field can contain one and only one value. However in a frame, each slot can have an unlimited number of values, or "facets".

It gets worse. The facets don't have to have alphanumeric or binary values; they can name programs that get control when the slot is changed or is referred to. A program that gets control when an arbitrary value is changed in a frame is called a "demon". Demons run independently of each other and in no particular sequence.

Facets can also name other frames. You can build networks of frames just as you can build hierarchical or relational networks in a database.