The bottom-up flow is another entry method to the BDC feature in IP integrator. If a block design for a RM (or even just a sub-module design) already exists in another project or in a storage repository, it can be added to the IP integrator project as a design source. To create a BDC for that BD, drag and drop the design source from the Sources window to the canvas of the top-level BD.
Figure 1. Bottom-Up Flow in a Block Design
Tip: This can be done on a blank canvas or one that already contains IP for the static part of the design.