Note:
Do not confuse subject and object with active and passive.Active and passive are semantic, they give 'meaning' to a relation. It is the relation which will dictate which participants (subjects or objects) in a composition are semantically active or passive.
For example when we have the relation "is hit by", then the subject in this relation will be semantically passive.
Assume we have a family with a grandparent, a parent and a child.
The following relations hold:
In the relation grandparent haschild parent, the grandparent is the subject.
In the relation parent haschild child, the parent is the subject.