URBAN5 searches for two types of consistency. It searches for conflicts and incompatibilities following a simple flow chart.
An incompatibility “error message” is a remark upon an incongruity between a designer’s action and a predefined requisite embedded in the machine. An incompatibility can cause the machine to signal the user (by ringing a bell and displaying the message on the top of the screen) but allow the action, or it can cause the machine to refuse to act in cases where the violation is severe. For example, a cube might be placed floating in midair. The machine would indeed draw the cube but simultaneously display the message that it was “not structurally possible at this time.” However, if a vertical surface is assigned the attribute of access (explicitly by the user) when there is no horizontal surface on one or both sides, URBAN5 refuses to make the qualification and alerts the designer of the problem. Although incompatibilities are simple relationships, overlooking them can be embarrassing or disastrous.
A conflict is an inconsistency discerned by the machine relating criteria specified by the designer to forms generated by the designer. A conflict is thus generated when there is an inconsistency between what the architect has said and what he has done. To state a constraint, the designer must enter INITIALize mode, describe a context, and push the “speak” button on the typewriter console. At this point he can type a criterion to the machine using the English language. The machine relies heavily upon the context of the designer’s activities to interpret the sentence. If it understands, URBAN5 asks, “How important is this criterion?” The designer’s reply defines to the machine how frequently it must survey the project in search for consistency between criteria and form. Also, the reply establishes a range of satisfaction for the machine to employ; that is, it governs the relative enforcement of the not-so-important constraints as opposed to the critical ones.
When URBAN5 finds an inconsistency between what has been said (linguistically) and what has been done (graphically), it states that a conflict has occurred, it quotes the designer’s statement of criterion, and it displays the present status of the situation. From here, the designer can take one of four courses: (1) he can change the form to be compatible with the criterion; (2) he can alter the criterion to be compatible with the form (now that he has learned that the issue may not be so important); (3) he can postpone the issue; (4) he can ignore the conflict (much to the chagrin of URBAN5).
This sort of interplay between form and criteria, architect and machine, begins to suggest a dialogue. The statements of criteria are deliberations on the designer’s behalf, issues he feels to be relevant. Discernments of inconsistency are noted temporally during the machine’s background work.