Unified modeling language (UML)6 is the de facto standard for representing object-oriented designs. It does a fine job of recording designs, but it has a severe problem: its diagrams don't convey what humans need to know, making the diagrams difficult to understand. This is why most software developers use UML only when forced to.1
For example, the UML diagrams in Figures 1 and 2 portray the embedded software in a fax machine. While these diagrams are attractive, they do not even tell you which objects control which others. Which object is the topmost controller over this fax machine? You don't know. Which object(s) control the Modem object? You don't know.