UML models help you understand, discuss, and design software systems. Visual Studio provides templates for five of the most frequently used UML diagrams: activity, class, component, sequence, and use case. In addition, you can create layer diagrams, which help you define the structure of your system.
UML modeling diagrams and layer diagrams can exist only inside a modeling project. Each modeling project contains a shared UML model and several UML diagrams. Each diagram is a partial view of the model. The UML model contains all the elements on the UML diagrams and can be viewed by using UML Model Explorer.