Composite Primary Key or Auto Increment key ?

Question

Hi.. i have two ways for make something and don't know what's better ......
Problem : 3 tables
Client ----> ( 1,* ) Activity -----> (1,1) ActivityAccreditation
A Client it can have one or more activities, and one Activity have one ActivityAccreditation. On Client the primary key is CLIENT_ID, the two ways for generate the keys on the other tables are :
a ) On Activity the primary key is composed by CLIENT_ID and SEQUENCE_ACTIVITY ( a number than increment value by CLIENT_ID, example : CLIENT_ID = 1122 could have SEQUENCE_ACTIVITY from 1 to 3 for three activities, and CLIENT_ID = 1122 could have SEQUENCE_ACTIVITY from 1 to 4 for four activities ), and ActivityAccreditation have CLIENT_ID and SEQUENCE_ACTIVITY and ACCREDITATION_TYPE ( a code ).
b) On Activity the primary key is ACTIVITY_ID ( auto increment number ) with the CLIENT_ID like foreign key only. And on ActivityAccreditation have ACTIVITY_ACCREDITATION_ID like primary key and ACTIVITY_ID like foreign key.
The situation is than the numer of rows could to grow very much in the time ( 3.000.000 rows on ActivityAccreditation in one year and the database to be supported each five years ) and we don't know what solution is better by performance......
Tks.

Answer 1

I prefer the surrogate key.
I don't like composite keys as a rule because they tend to inject business logic into keys. Using surrogate keys eliminates this possibility.
For performance reasons, this means that you might want to create additional indexes on those columns to facilitate fast access. But my prejudice is to stick with surrogate keys.
I will admit that I'm not a DBA, so there are certain to be alternative views and arguments. We'll see if any of them pop up on this thread.