# Diagrammatic Reasoning in AI

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A Classification of Diagram Types

Diagrams are information graphics that are made up primarily of geometric shapes such as rectangles, circles, diamonds, or triangles, that are typically (but not always) interconnected by lines or arrows.  One of the major purposes of a diagram is to show how things, people, ideas, activities, etc. interrelate and interconnect.  Unlike charts and graphs, diagrams are used to show interrelationships in a qualitative way.

The figure below illustrates the classification hierarchy for six categories of diagramming, as well as the different types of diagrams, under each category.  This figure serves as the outline for the discussion of diagramming techniques discussed in Chapter 3 of the book.  Click one of the links to get more information about the diagram type.

 1.      System Topology2.      Sequence and Flow 3.      Hierarchy and Classification4.      Association 5.      Cause and Effect 6.      Logic Reasoning

One difficulty in creating diagrams is that there are such an enormous variety of types.  One can easily become overwhelmed by the huge number of notations and techniques that are employed in the different domains.  There are literally hundreds of examples in specific domain areas including:  circuit and logic diagrams employed by electrical engineers to help them design and troubleshoot circuit boards; entity-relationship diagrams that later serve as blueprints for how a database application is created; Pert Charts that project managers can use for scheduling and planning complex projects composed of many different tasks, some of which can be executed concurrently; and web site maps that illustrate the structure of the web site that web designers are planning to build.  Indeed, in many different fields and walks of life, diagramming is an important skill that aids in understanding, communicating, and in many cases, implementing complex systems and ideas.

Given the vast number of techniques that have been employed by the different domain areas, it would be impossible to cover all the different types of diagramming within a single chapter, or even within a single book.  However, it is also clear from a survey of these techniques that a number of themes cut across the great diversity of diagrams in use today.  Chapter 3 of the book describes a classification of the major types of diagrams that are possible, organized around six major themes (system topology; sequence and flow; hierarchy and classification; association; cause and effect; and logic reasoning).

What advantages do diagrams have over verbal descriptions in promoting system understanding?  First, by providing a diagram, massive amounts of information can be presented more efficiently.  A diagram can strip down informational complexity to its core—in this sense, it can result in a parsimonious, minimalist description of a system.  Second, a diagram can help us see patterns in information and data that may appear disordered otherwise.  For example, a diagram can help us see mechanisms of cause and effect, or can illustrate sequence and flow in a complex system.  Third, a diagram can result in a less ambiguous description than a verbal description, because it forces one to come up with a more structured description.  By necessity, the notations of the diagramming language, which serve as its vocabulary, circumscribe what is and what is not allowed in the diagrammatic representation.