Role : A group of activities normally (but not always) performed by one person and often implemented with a security group. Often, one person may play multiple roles.
Constituency (Team of peers ): Just like; Product Management, Program Management, User Experience, Architecture, Development, Test, Release and Operations. All these are constituencies in development process. These constituencies works for reducing risk and increasing the likelihood of a successful project.
Difference between Role and Constituency : For example you got role as Developer and you belong to Development. if you are User Experience Architect, you belong to "User Experience".
Advocacy Group's definition according to MSF :
Development Constituency has Developer, Lead Developer, Development Manager, Build Engineer roles . For example: You are developer, you have a friend named Maria, she is development Manager. You have another friend named Josh, he is Build Engineer and you have another friend more named Onur :). he is Lead Developer.
Now. You, Maria, Josh and Onur is Advocacy Group, together in this development process. Just like this.
I hope I help you understand.
just code it