I would like to know what you think about single vs multiple primary key fields designs.

Sample db design:
Customer - Project - Activity. One customer have many projects. One project have many activities.

Multiple PK design:
Table Activity has threee fields as primary key:
- projectID
- customerID
- activityID
The combination of theese thre are unique. Sample table data
CustID ProjID ActId
1 1 1
1 1 2
1 2 1
2 1 1

Single PK design:
Table Activity has one single unique field as PK:
- ActivityID
Sample table data
CustID ProjID ActId
1 1 1
1 1 2
1 2 3
2 1 4

Project and Customer are referred with foreign keys (which are indexed).

Pro multiple:
I find it easier to track/debug activity data in database.
Cons multiple:
It's more work to create activityID restarting from 1 for each cust/proj combo.

For single PK the pro/cons is the opposite.

What do you think?

Regards,
Micael

Its always better to have single PK if its possible ...... but there are some places where you can not have single PK in tat case you need to use multiple PK .