Composite Software offers a new level of granularity when compared to SaaS (Software as a Service). Composite Software is about enabling "right-sourcing", i.e. move (or keep) arbitrary small or large elements of functionality wherever it is the most cost effective to operate them, not just entire systems. Economically, "right-sourcing" is far more efficient than "outsourcing" and SaaS.
Domain Driven Design is a vision and approach for designing a domain model that reflects a deep understanding of the business domain. This book is a short, quickly-readable summary and introduction to the fundamentals of DDD; it does not introduce any new concepts; it attempts to concisely summarize the essence of what DDD is, drawing mostly Eric Evans' book.