Segments that can be in virtual storage simultaneously are considered inclusive. Segments in the same region but not in the same path are considered exclusive; they cannot be in virtual storage simultaneously. Figure 1 shows the inclusive and exclusive segments in the sample program.

Figure 1. Inclusive and exclusive segments

Segments upon which two or more exclusive segments are dependent are called common segments. A segment common to two other segments is part of the path of each segment. In Figure 1, segment 2 is common to segments 3 and 4, but not to segment 5.

An inclusive reference is a reference between inclusive segments, from a segment in storage to an external symbol in a segment that does not cause overlay of the calling segment. An exclusive reference is a reference between exclusive segments, a reference from a segment in storage to an external symbol in a segment that causes overlay of the calling segment.

Figure 1 shows the difference between an inclusive reference and an exclusive reference. The arrows indicate references between segments.