The Formal Description of Data Types Using Sketches. - Charles Wells; Michael Barr (MFPS, 1987)

Category theory for computing science. - Michael Barr; Charles Wells (Prentice Hall, 1990)

A Generalization of the Concept of Sketch. - Charles Wells (Theor. Comput. Sci., 1990)

A Formalism for the Specification of Essentially Algebraic Structures in 2-Categories. - A. John Power; Charles Wells (Math. Struct. Comput. Sci., 1992)

Category theory for computing science (2. ed.). - Michael Barr; Charles Wells (Prentice Hall, 1995)

Graph-based Logic and Sketches - Atish Bagchi; Charles Wells (CoRR, 2008)