Authors 
Title 
Status, Abstract 
Gunther Schmidt 
Rectangles, Fringes, and Inverses.pdf .bib 
Relational Methods in Computer Science, RelMiCS 10April 612, 2008, Frauenwörth, GermanyProceedings appeared as Lect. Notes in Comput. Sci. 4988 (352366) 
Universität der Bundeswehr München 85577 Neubiberg, Germany Gunther.Schmidt@UniBw.de 

Relations and graphs are widely used as modeling tools. Relational composition is an associative operation; therefore semigroup considerations often help in relational algebra. We study here some less known such effects and relate them with nonenlargable rectangles inside the relation, i.e., with the basis of concept lattice considerations. The set of points contained in precisely one nonenlargable rectangle makes up the fringe. We show that the fringe sometimes acts as a generalized inverse of a relation. Regular relations have a generalized inverse. They may be characterized by an algebraic formula. 