I´m struggling how to decompose a sprint in SCRUM. I know in many cases SCRUM is used only for the developing part in the software process, but I want to use it for the whole project (in our case: prestudy analysis, purchase from suppliers, and development.
If I decompose a sprint based on a time limit (e.g. 2-3 weeks each), then the sprint will contain unrelated features as I see it. For e.g. same sprint will contain "prestudy of X", "purchase of Y", "development of Z", etc. Only relation between the features in the sprint will be that they are from the same backlog. The problem is with this case is that it will be hard to find a common sprint goal.
If I instead decompose a sprint based on features, for e.g. one sprint for "prestudy feature X", and another sprint for "prestudy feature Y", then it is easy to have a clear sprint goal for each sprint. On the other hand, this leads to some architects having to work on several sprints in parallel. That is because each and every prestudy require that we involve external consultants. Our architect will more or less just hand over the job to the consultant for the particular prestudy and the consultant will do the rest. So the architect will have time to manage several prestudies in parallel. The problem with this case is that there is a rule of thumb in SCRUM that a person shall not work with several sprints at the same time.
Need some guidance here how to add features in a sprint. If you decompose based on time, how do you create a clear sprint goal? If you decompose on features, do your team work with several sprints in parallel?