Facets are annotations on slots.
The GFP uses facets as a means of defining constraints, restrictions and defaults on frames, slots and slot-values. To this effect, a set of standard facets have been defined. The GFP also supports a more general use of facets to annotate slots with arbitrary values, but this use has no corresponding expression in Loom. We hope this measure will be just a temporary one. The standard facets available in GFP, and their corresponding interpretations in Loom, are described below.