1. Activity Diagram

2. Introduction
Technique to describe procedural logic, business process, and work flow.
Activity diagram is basically a flow chart to represent the flow form one activity to another activity(operation of the system). Flow can be sequential, branched or concurrent. 
Also used to construct the executable system by using forward and reverse engineering techniques.
Activity diagram cannot be exactly matched with the code. The activity diagram is made to understand the flow of activities and mainly used by the business users.

3. Comparison with other behavior diagram
Interaction & State chart diagrams are used to show the message flow from one object to another.
Activity diagram is used to show flow from one activity to another. It does not show any message flow from one activity to another. 

4. How to draw? Before drawing an activity diagram,
Have a clear understanding about the elements used in activity diagram.
Identify the activities (function performed by the system).
Identify Association, Conditions & Constraints
Once the above mentioned parameters are identified, make a mental layout of the entire flow.
This mental layout is then transformed into an activity diagram.

6. Components in diagram
An activity refers to a sequence of actions, so the diagram shows an activity that's made up of actions.
Initial node & Final node (Node represent Action)
Flow edge
A fork has one incoming flow and several outgoing concurrent flows.
A Join – One outgoing flow is taken only when all the incoming concurrent flows reach the join.

7. Parallelism or Concurrency
When you have parallelism, you'll need to synchronize.
This is important for business modeling because processes often occur in parallel.
It's also useful for concurrent algorithms, in which independent threads can do things in parallel.
Notations used: Fork & Join

8. Decision & Merge
Conditional behavior is delineated by decisions and merges.
A decision has a single incoming flow and several guarded out-bound flows.
Boolean condition is placed inside square brackets. The guards should be mutually exclusive in out-bound flows.
A merge has multiple input flows and a single output. It marks the end of conditional behavior started by a decision notation.

9. Decomposing an Action
Actions can be decomposed into subactivities.

10. Actions can be implemented either as subactivities or as methods on classes. Show a subactivity by using the rake symbol and call on a method with syntax classname::method-name

11. Partitions
Activity diagrams tell you what happens, but they do not tell you who does what.
In programming, the diagram does not convey which class is responsible for each action.
In business process modeling, this does not convey which part of an organization carries out which action.
Divide an activity diagram into partitions, which show which actions one class or organization unit carries out.

12. Partitions: simple one-dimensional partitioning referred as swim lanes
Partitions: simple one-dimensional partitioning referred as swim lanes. Also take each dimension and divide the rows or columns hierarchically.

13. Signals Actions can also respond to signals.
A time signal occurs because of the passage of time. Eg: End of a month in a financial period or Each microsecond in a real-time controller.
Signal indicates that the activity receives an event from an outside process. So the activity constantly listens for signals

14. Signals Cond...