6. DETAILS OF VMACS

The vmacs litany is that it provides "performance agility plus processing power". But what is performance-grade agility? Agility can be gauged in text-graphic manipulations per second. vmacs achieves agility through a touch-typing interface with no waiting for menus (Lakin, 1986b). And processing power means that vmacs has the ability to interpret a spatial arrangement of text-graphic objects as an expression in a visual language and then take appropriate (assistive) action. Processing a visual expression in vmacs occurs in two stages: parsing and semantics. Parsing is the recovery of the underlying syntactic structure from the spatial arrangement of the elements; that structure is then used in the semantic stage, where procedures deal with how the parsed expressions carry meaning and what appropriate actions are. Spatial parsing and semantic processing is discussed in more detail in (Lakin, 1980c, 1986a, 1987).

Many computer graphics systems offer processing of visual languages, but the editors in these systems are "hard-wired" for a particular visual language. The advantage of vmacs is that processing is supported in the midst of general purpose blackboard activity. The relation of processing to this activity is shown in Figure 6. Blackboard activity is live and spontaneous, general and unstructured      a kind of "conversational graphics". In contrast, an expression in a particular visual language is highly structured according to the rules for laying out phrases in that language. The most natural way for expressions in visual languages to occur is embedded in conversational graphics. These expressions can be viewed as locally-coagulated lumps in the more general text-graphic stuff ("text-graphic oatmeal") generated during blackboard activity. vmacs has the capability to process such lumps when they occur in the midst of conversational graphics.