UML sequence diagram - Help desk
"A help desk is a resource intended to provide the customer or end user with information and support related to a company's or institution's products and services. The purpose of a help desk is usually to troubleshoot problems or provide guidance about products such as computers, electronic equipment, food, apparel, or software. Corporations usually provide help desk support to their customers through various channels such as toll-free numbers, websites, instant messaging, or email. There are also in-house help desks designed to provide assistance to employees." [Help desk. Wikipedia]
The UML sequence diagram example "Help desk" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Rapid UML solution from the Software Development area of ConceptDraw Solution Park.