Source : Free On-Line Dictionary of Computing

Xy-pic
     
         A package for {typesetting} graphs and
        diagrams using {TeX}.  It is structured as several modules,
        each defining a custom notation for a particular kind of
        graphical object or structure.  Example objects are arrows,
        curves, and frames.  These can be organised in matrix,
        {directed graph}, path, polygon, knot, and 2-cell structure.
     
        Xy-pic works with {LaTeX}, {AMS-LaTeX}, {AMS-TeX}, and {plain
        TeX}, and has been used to typeset complicated diagrams from
        many application areas including {category theory}, {automata}
        theory, {algebra}, {neural networks} and {database} theory.
     
        {Home (http://www.ens-lyon.fr/~krisrose/Xy-pic.html)}.
     
        (1997-11-20)