Join and merge activity diagram

Question

What’s the difference between Join and Merge in the Activity Diagram?

I would like a simple example of each of them to better understand.

Answer 1

About the Merge (See the reference 1)

Merge is a control node that brings together several alternative flows input to accept the single output stream. There is no token merge. The merge should not be used to synchronize simultaneous streams - A merge brings together multiple streams without synchronization.

About the Join (See the reference 2)

Join is a control node that has multiple input edges and an output edge and is used to synchronize simultaneous input streams. Joins are introduced to support parallelism in activities .

For example, in the diagram below:

• Every time I refer to merged or merged, it is understood that I am talking about a merge.

A decision is used after a Fork, the two flows that come out of the decision need to be merged (Merge) into one, so go to a Join.

Why? Otherwise, Join will wait for the two flows.

So , Activity2 and Activity3 are ours alternative flows and only one of them it will. And they nay are synchronizing the input.

However, the Concurrent_activity and the outcome of the decision between Activity1 and Activity2(which is merged (merge) into an output) are synchronizing the simultaneous input streams. Join expects both to work and continue.

Answer 2

A Merge is represented graphically by a rhombus with two or more inputs and only one output, for example: When paying the parking the flow would be : Note that regardless of the payment choice the flow converges to a single output.

A Join, is represented by a solid bar that has two or more inputs and an output, understand it as a synchronization of parallel activities, when making a purchase in e-commerce the flow would be : Note that the two activities do not depend on each other, but only after both have been completed can you move on to the next.

You can use this material to ask more questions about these elements : http://www.theclub.com.br/restrito/revistas/201310/umld1310.aspx