Hartmut Ehrig & Bernd Mahr 
Fundamentals of Algebraic Specification 1 [PDF ebook] 
Equations and Initial Semantics

The aim of this book is to present fundamentals of algebraicspecifications with respect to the following three aspects:fundamentals in the sense of a carefully motivatedintroduction to algebraic specifications, which is easy tounderstand for computer scientists and mathematicians;fundamentals in the sense of mathematical theories which arethe basis for precise definitions, constructions, results, and correctness proofs; and fundamentals in the sense ofconcepts, which are introduced on a conceptual level andformalized in mathematical terms. The book is equally suitableas a text book for graduatecourses and as a reference for researchers and systemdevelopers.