D.1.1 Forward Chaining
Programming Expert Systems in OPS5, An Introduction to Rule-Based Programming
by Lee Brownston, Robert Farrell, Elaine Kant and Nancy Martin (Addison-Wesley). Whilst being specifically on OPS5 this text covers most aspects of forward chaining in considerable detail.
KnowledgeWorks and Prolog User Guide (Unix version) - 29 Feb 2008