WHAT ARE FRAMES?
Natural language understanding requires inference i.e., assumptions about what is typically true of the objects or situations under consideration. Such information can be coded in structures known as frames.
NEED OF FRAMES
Frame is a type of schema used in many AI applications including vision and natural language processing. Frames provide a convenient structure for representing objects that are typical to a stereotypical situations. The situations to represent may be visual scenes, structure of complex physical objects, etc. Frames are also useful for representing commonsense knowledge. As frames allow nodes to have structures they can be regarded as three-dimensional representations of knowledge.
A frame is similar to a record structure and corresponding to the fields and values are slots and slot fillers. Basically it is a group of slots and fillers that defines a stereotypical object. A single frame is not much useful. Frame systems usually have collection of frames connected to each other. Value of an attribute of one frame may be another frame.
A frame for a book is given below.
| Slots | Fillers |
|---|---|
| publisher | Thomson |
| title | Expert Systems |
| author | Giarratano |
| edition | Third |
| year | 1998 |
| pages | 600 |
The above example is simple one but most of the frames are complex. Moreover with filler slots and inheritance provided by frames powerful knowledge representation systems can be built.
Frames can represent either generic or frame. Following is the example for generic frame.
| Slot | Fillers |
|---|---|
| name | computer |
| specialization_of | a_kind_of machine |
| types | (desktop, laptop,mainframe,super) if-added: Procedure ADD_COMPUTER |
| speed | default: faster if-needed: Procedure FIND_SPEED |
| location | (home,office,mobile) |
| under_warranty | (yes, no) |
The fillers may values such as computer in the name slot or a range of values as in types slot. The procedures attached to the slots are called procedural attachments. There are mainly three types of procedural attachments: if-needed, default and if-added. As the name implies if-needed types of procedures will be executed when a filler value is needed. Default value is taken if no other value exists. Defaults are used to represent commonsense knowledge. Commonsense is generally used when no more situation specific knowledge is available.
The if-added type is required if any value is to be added to a slot. In the above example, if a new type of computer is invented ADD_COMPUTER procedure should be executed to add that information. An if-removed type is used to remove a value from the slot.