Equational specifications of abstract data types can be considered
as certain graphs enriched by equations. We introduce a category spec of such
specifications and show that spec has pushouts. Moreover, there is a forgetful
functor from spec to the category graph of graphs, respecting pushouts. Thus,
the patterns of graph replacement by means of pushouts are applicable to
specifications. We discuss parametric specifications and parameter substitution
on these grounds, and we give an example for a more general replacement
operation in analogy to a graph production.