Showing an association between an activity and a block on a block definition diagram (SysML)
A Block Definition Diagram can show a Uni-directional Association between an Activity and a Block. The Association represents an object node (Data Store, Central Buffer, Input Pin or Output pin) that uses the Block as its type and is owned by the Activity. As such, when you select the Association on the Block Definition Diagram, the Property Pages show the properties of the object node.
To show an association between an activity and a block:
1. On the diagram's tab, click the 
Uni-Directional Association button.
Uni-Directional Association button.2. Click the Activity, and then click the Block.
3. If a popup menu appears, click the command for the object node you want to show.
Alternatively,
Right-click the Activity, Block or diagram background, point to Populate, point to Links, and then click Associations.