(A couple of these are unfair of me in that they are not explicitly answered in the videos. Try anyway!)
Q1 Activities in a UML activity diagram are shown as
Q2 The key symbol involved in showing more than one thing happening
in parallel is
a thick black bar
a diamond
a circle
a special kind of arrow
Q3 Two arrows could legally come out of the same activity:
True
False
Q4If two arrows go into a thick black bar, and then one arrow comes
from the bar into an activity A, then removing the black bar and making the
original two arrows go straight into A would:
make no difference to the meaning
of the diagram
make a difference to the meaning of
the diagram
make the diagram illegal
Answers:
Q1: rectangles with rounded corners
Q2: a thick black bar
Q3: true, technically, but I strongly recommend not doing this when you write diagrams, because the UML specification is confusing and to some extent inconsistent. Depending on whether you want one of the arrows to be followed or both, use a decision diament or a fork bar.
(When you do see this done in diagrams, there will usually be conditions on the arrows, only one of which can evaluate to true, so that in any actual situation only one arrow can be followed. If not, the diagram is non-deterministic.)
Q4: well, it doesn't make the diagram illegal, although it would have done in UML1. Fork bars and join bars used to have to occur in pairs. Now they don't. Whether it makes a difference: the UML specification is confusing and somewhat inconsistent. If you see an activity written with two arrows coming into it, the most likely intended meaning is that either arrow can cause the activity to start. This contrasts with the unambiguous meaning of two arrows going into a join bar which then has one arrow into an activity: in this case, both incoming arrows have to be traversed by a control token before the arrow into the activity can be traversed. However, because of the ambiguity, I strongly suggest never writing an activity diagram with two arrows going into the same activity. Use either a join bar, or a merge diamond, depending on which meaning you want.
If in doubt, review.