There is only one file type that uses the .UML extension:
UML Data Object Model
Object model description created using the Unified Modeling Language (UML), a standard way of describing objects in an XML format; used in software development and may include a list of elements and classes associated with a program object.
UML files are typically generated during the software design process. Developers often submit them for peer review and refine them before implementation. Once approved, the UML data can be used to auto-generate source code so that the developer does not have to manually type the code.
The Eclipse IDE is a popular development environment that supports UML files. They can be viewed in a hierarchical format or as a visual diagram. Editing the visual diagram within Eclipse updates the corresponding UML file.
Updated: October 19, 2010