What is the purpose of an activity diagram?

Answer 1

The purpose of the activity diagram is to model the procedural flow of

actions that are part of a larger activity. In projects in which use cases are

present, activity diagrams can model a specific use case at a more

detailed level. However, activity diagrams can be used independently of

use cases for modeling a business-level function, such as buying a concert

ticket or registering for a college class. Activity diagrams can also be used

to model system-level functions, such as how a ticket reservation data

mart populates a corporate sales system's data warehouse.

Because it models procedural flow, the activity diagram focuses on the

action sequence of execution and the conditions that trigger or guard

those actions. The activity diagram is also focused only on the activity's

internal actions and not on the actions that call the activity in their process

flow or that trigger the activity according to some event (e.g., it's 12:30

on April 13th

, and Green Day tickets are now on sale for the group's

Copyright Rational Software 2003 http://www.therationaledge.com/content/sep_03/f_umlbasics_db.jspsummer tour).

Although UML sequence diagrams can protray the same information as

activity diagrams, I personally find activity diagrams best for modeling

business-level functions. This is because activity diagrams show all

potential sequence flows in an activity, whereas a sequence diagram

typically shows only one flow of an activity. In addition, business

managers and business process personnel seem to prefer activity

diagrams over sequence diagrams -- an activity diagram is less "techie" in

appearance, and therefore less intimidating to business people. Besides,

business managers are used to seeing flow diagrams, so the "look" of an

activity diagram is familiar.

(reference by http://www.ibm.com/developerworks/rational/library/content/RationalEdge/sep03/f_umlbasics_db.pdf)