5.2 VISUALIZATION
5.2.2 CLASS-INSTANCE PAIRS
The individual entities of the CAD system above - parts, features, images, critiques, and properties - are atoms that do not, in and of themselves, provide insight into a concurrent engineering system. More than the individual entities themselves, it is the relationships between and including these elements that serve to define the nature of concurrent engineering systems. These relationships and their entities - these molecules of the system - are akin to those explored in literature theory as the "sign".
A linguistic sign is defined by Saussure to be an ordered pair of the signified and the signified. The signified is a concept, such as feline, while the signifier is a linguistic expression of that concept, as in the sound-image cat. Figure 56 (a) and (b) depict Saussure's illustration of the linguistic sign. The arrows denote the intimate coupling of the signifier and signified, with one tied to the other in conceptualization and expression. In (b) The signified is a concept, such as denoted here by the image of a feline, while the signifier is a linguistic expression of that concept, as in the sound-image cat.
In other semiotic literature, de Saussure's union of the sign is expressed in terms of object and icon, or connoted and denoted among others. A survey of semiotic literature reveals generally little agreement in the jargon to use; often a variety of words is used to describe the same concepts or the same word is used to describe different concepts.
This section will methodically build upon the Class-Instance Pair (CLIP) Model of [Glinert & Gonczarowski 87]. The CLIP model is used to develop a formal model for visual programming languages. One basic unit is the i-instance, which correlates highly with Saussure's sign. The components of the i-instance are the object and the icon, with definitions identical to the signified concept and the signifier expression. The use of the term icon is appropriate in light of the earlier exposition for the icon in the CLIP model may represent and stand in place of the underlying object.
Illustrated examples will be given at each stage to depict the visual relationships of the items under examination. The examples will use the visualization of PIMES critiques within the DFM system. The concepts will be extended to include object manifestations other than visual manifestation. Although not formally implemented, the visualizing system as well as the DFM system itself could be characterized under the formalism in future work. The CLIP-based formalism is presented here to emphasize that there is distinction between the original concept or model and the sign that represents it while, at the same time, the two items are intimately linked.