My old friend Carsten Ziegler and some colleagues just published a new book on business rules in an SAP environment in German: Business Rules Management mit ABAP
The book is designed to help you integrate business rules with your ABAP environment. It shows how to model business rules in BRFplus to support and automate decisions. It discusses the benefits of SAP Decision Service Management for system-wide implementation as well how to work with decision tables, decision trees, formulas and other types of rule expressions.It also has information on deployment scenarios, application development approach and a worked example.
I wrote a foreword for them (Carsten assures me he translated it accurately) as I did for his last book on BRFplus. I also worked with him on content for Applying Real-World BPM in an SAP Environment.