The framework of each discipline
Brazilian jiu-jitsu favors control and transitions on the ground in its common forms. The Shotokan mainly studies standing actions. Japanese jujutsu, for its part, brings together several traditions and should not be confused with a single ground method.
What comparison teaches
The ability to control ground position and the ability to manage striking distance are two different issues. Cross training requires explicit instructions: a submission is not a technique to be improvised on an unprepared partner. No style guarantees success in all situations. A useful comparison looks at the same exercise, comparable level and explicit instructions. The club, the teacher and the regularity of the practice count as much as the etiquette of the discipline.
Ground position control
A relationship on the ground involves support and means of movement different from those of a standing exchange. In Brazilian jiu-jitsu, position, transitions and control possibilities are central subjects of study. The practitioner of Shotokan who discovers this field benefits from learning its vocabulary and its conventions before looking for connections. A partner must be able to report the stop and be heard immediately. Comparing disciplines allows you to identify an area that has received little attention in one; this does not demonstrate that the other covers all situations.
Understand progression on the ground
During a Brazilian jiu-jitsu class, identify the starting positions, the conditions for success and the way to announce the stop. The progression can relate to an exit from a position before moving to a submission. The experience of kata does not replace this reading of the supports and the partner on the ground. For a jujutsu course from another tradition, ask for the exact program: the weapons, projections or possible strikes change the framework of comparison.