Why UML? Many people appear to think that modelling is only for academic textbooks and school. Several months ago I worked on a project that failed, for numerous reasons, but some of the reasons were mine. So I set out to figure what it was that I didn’t know, that would have allowed me to build this system I had been asked to. After reading Patterns of Enterprise Application Architecture, Domain-Driven Design: Tackling Complexity in the Heart of Software, and Design Patterns: Elements of Reusable Object-Oriented Software and realizing that all of the great books used UML.