  Qualitative approaches to space were introduced into the logical literature early in the twentieth century by Lesniewski; see  Lesniewski 1916,  which presents the idea of a mereology, or qualitative theory of the part-whole relation between physical individuals. This idea of a logical theory of relations among regions or the objects that occupy them, which does not depend on construing regions as sets of points, remained an active area of philosophical logic, even though it attracted relatively few researchers. More recent work in the philosophical literature, especially  Casati &amp; Varzi 1999,  Simons 1987,  Casati &amp; Varzi 1996,  Clarke 1981,  Clarke 1985,  as directly influential on current computational work.