Unified Modeling Language (UML) was introduced to create a standardized way of visualizing a software system design. It was developed by Grady Booch, Ivar Jacobson, and James Rumbah at Rational Software in the mid-nineties. It was adopted as a standard by the Object Management Group in 1997, and also by the International Organization for Standardization (ISO) as an approved ISO standard in 2005.

The UML standard actually provides many different kinds of diagrams for describing a software system - both structure and behavior:

  • Class Diagram A class diagram visualizes the structure of the classes in the software, and the relationships between these classes.
  • Component Diagram A component diagram visualizes how the software system is broken into components, and how communication between those components is achieved.
  • Activity Diagram An activity diagram represents workflows in a step-by-step process for actions. It is used to model data flow in a software system.
  • Use-Case Diagram A use-case diagram identifies the kinds of users a software system will have, and how they work with the software.
  • Sequence Diagram A sequence diagram shows object interactions arranged in chronological sequences.
  • Communication Diagram A communication diagram models the interactions between objects in terms of sequences of messages.

The full UML specification is 754 pages long, so there is a lot of information packed into it. For the purposes of this class, we’re focusing on a single kind of diagram - the class diagram.