BAM question: Update existing data

I’ve been thinking to use BAM in my current project as a primary logging source, have been thinking a scenario like this:

An person’ applies for product and the goal is to log/update the information about this person

• How do I tell if this person exists in the database?
• Say this person information already in the BAM database, how do I tell BAM: find the exisiting activity ID of this person so that I can reference other activities with it?
• Say this person changes his address, how do I instrument BAM to change accordingly?

Thanks advance for any help!