Does time go downward in an UML sequence diagram?

Question

I believe that in any UML sequence diagram, time goes downward (and to the right), for example:

2013

2014

2015

2016

So the end would be at the bottom and (optionally) to the right. Is this in fact the case? The reason for asking is that I want to verify that a manager indeed wants the opposite of an UML sequence diagram, i.e. a manager has explicitly said that he prefers in this case is a time sequence stated with the latest update first e.g.

2016

2015

2014

2013

which is the opposite of UML. I don't mind either way but I feel reluctant to keep 2 standards at once for the same procedure. So what I'm asking is whether it's correct to say that my manager indeed want the opposite of the way an UML sequence diagram is?

Answer 1

You're right: in a sequence diagram, time is understood to pass from the top to the bottom. If you want to change it and make time pass from the bottom up, you will have to put the swimlane's labels at the button, or you'll have issues with swimlane creation if one happens during the sequence (i.e. a message creates a new object with its own swimlane).

Similarly, activity diagrams are understood to be represented with time moving from top to bottom or from left to right.

Answer 2

By UML definition, time goes downward, but time for individual lifeline is mutually independent. It means, that points (occurrences) placed at the same position from top on two lifelines does not have to occur at the same time ! See traces definition of interactions in UML superstructure.