Since version 6.0, astah* allows you to adjust the length both of Execution Specifications and Lifelines in Sequence diagrams by Pop-up menu. By adjusting them, you can easily make your sequence diagrams look nicer and also save some space on the paper if you print them.

Let me show you how to do so with an example.
At first, you have a sequence diagram as the figure below.













There are three things you can do to it.




(1) Shorten the Execution Specification
(2) Shorten both Execution Specifications
(3) Shorten the lifeline






Let's start with the (1). Select the Execution Specification and select [Adjust Execution Specification Length] from its Pop-up menu.













The size of the Execution Specification becomes the shortest as it can be.













Now let's go to the (2). Select both Execution Specifications and select the same menu.











Both selected Execution Specifications got shorter.











At last, you want to adjust lifelines. Right-click on diagram without selecting any models. So a Pop-up menu appears, select [Adjust Lifeline Length] - [Default]









[Default] makes each Lifeline to be the shortest as it can be.















[Align to Minimum] detects the length of the shortest lifeline in the diagram and adjust all other lifelines to be the same length. So the end of all the lifelines are all in one line (i.e. the figure below)






On the other hand, [Align to Maximum] detects the length of the longest lifeline in the diagram and do the same.









So now it completes. You can see a big difference in the before-after figure below.