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Unit 8: Structured Representation of Knowledge

Self Assessment Notes

State whether the following statements are true or false:
7. Phrase structure rules specify how an initial symbol can be recursively expanded into a
sequence of other symbols.
8. A symbol can be expanded in a one way.

8.5 Frames and Frame Systems

Many of the ideas about frame systems were first introduced in a unit by Marvin A. Minsky,
entitled “Framework for Representing Knowledge,” which appeared in P. H. Winston (Ed.), The
Psychology of Computer Vision. NY: McGraw-Hill, 1975. Pp. 211-277. In this unit, Minsky
introduces and argues for the idea of representing common sense knowledge in a data-structure
that he calls a frame. His motivation for introducing these ideas is indicated immediately at the
start of this unit where he states:
“It seems to me that the ingredients of most theories both in artificial intelligence and in psychology have
been on the whole too minute, local and unstructured to account either practically or phenomenologically for
the effectiveness of common sense thought. The “chunks” of reasoning, language, memory and “perception”
ought to be larger and more structured, and their factual and procedural contents must be more intimately
connected in order to explain the apparent power and speed of mental activities.”

A frame is a data-structure for representing a stereotyped situation, like being in a certain kind
of living room, or going to a child’s birthday party. Attached to each frame are several kinds of
information. Some to this information is about how to use the frame. Some is about what one
can expect to happen next. Some is about what to do if these expressions are not confirmed.

We can think of a frame as a network of nodes and relations. The “top levels” of a frame are
fixed, and represent things that are always true about the supposed situation. The lower levels
have many terminals- “slots” that must be filled by specific instances or data. Each terminal can
specify conditions its assignments must meet. (The assignments themselves are usually smaller
“subframes.”) Simple conditions are specified by markers that might require a terminal
assignment to be a person an object of sufficient value, or a pointer to a sub-frame of a certain
type. More complex conditions can specify relations among things assigned to several terminals.
Collections of related frames are linked together into frame systems. The effects of important
actions are mirrored by transformations between the frames of a system. These are used to make
certain kinds of calculation economical, to represent changes of emphasis and attention, and to
account for the effectiveness of imagery.”
As these ideas were realized in various “frame systems,” a rough agreement emerged concerning
exactly what constituted a frame. Below is listed these components.

A frame is a data structure that typically consists of:
Frame Name

Slot-filler (relations target)
default values
constraints on values within the slots of a frame

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