A system boundary element is a non-UML element used to define conceptual boundaries. You can use boundaries to help group logically related elements (from a visual perspective, not as part of the UML model).
Configuring Boundary Elements
Boundary elements can be configured to display in different ways. The main differences are:
|·||With horizontal or vertical 'swim lanes'; swim lanes are used to group elements in a vertical or horizontal context (eg. Client, Application and Database tiers could be represented in swim lanes).|