This is the most typical example of key mapping: An object name is mapped to the object itself.

On sheet The KEYVALUE function of the example workbook, the formula in cell B8 returns the area of a certain polygon.

Figure 18. The value assigned to key Polygon, i.e., "Triangle" is mapped to an object (the triangle, itself).

Notice that value assigned to key Polygon is the text "Triangle". Rather than a text, the processor Area requires a polygon to computes its area. Therefore, when the processor asks for the value associated to key Polygon, KeyValue maps the text "Triangle" to a polygon which is passed over to the processor.

More precisely, the text names a data set which is stored by the repository and defines an object. When an object is required the named data set is retrieved and passed over to a processor (defined by key Processor) which creates the object. Then, the object is returned to the processor which has initiated the call.

A text is mapped to some other basic type. For instance, consider the key Month. The user might prefer to provide text values: "Jan", "Fev", ..., "Dec". On the other hand, for the processor, numbers 1, 2, ..., 12 might be more convenient.

This mapping is very similar to the lexical conversion from "Yes" to TRUE as discussed in section Section 10. The difference is that opposite to lexical conversions, flag map depends on the key. For instance, for the key Planet the text "Mar" might be mapped to something representing the planet Mars (e.g. the number 4 since Mars is the forth planet of our solar system) rather than the month of March.

Like flag map, a text is mapped into a number or date. However, the user can also provide the corresponding number or date instead of the text.

For instance, the key NumberOfEdges used in our example workbook implements a partial map. Its value must be an integer greater than 2. For some special values (not all) there correspond a polygon name (e.g "Triangle" for 3 or "Square" for 4). There is no special name for a regular polygon with 1111 edges. To see this mapping in action, go to sheet Key mappings and change the value of NumberOfEdges in data set Polygon #6 to "Triangle" or "Square" or 1111 and see its area on E2.

Figure 19. Key NumberOfEdges implements partial map. Assigning to it "Square" is the same as assign it to 4.

Finally, there is the identity map (a.k.a no map): The text which is assigned to the key is retrieved by KeyValue and passed to the caller as it is.