Determine if a mesaure is aggregable or not in datawarehouse : can someone please tell me a 'general use', step-by-step method to find out what are the non-aggregability in a datamart. Here an example I found:

Notes: italic means 'key', bold identifies 'shortenings', 'column' is an alias for 'referencing'

> Relational schema:
> 
> **CAL**L(*COD*,DATE,FROM:S,TO:S,LEN)
> 
> **SIM**(*SIM*, USER:USER, TRIFF:T, BONUS)
> 
> **TAR**IFF(*TARIFF*, CARRIER:CAR)
> 
> **USE**R(*USER*, TOWN:TOW, LAST_TARIFF:TAR)
> 
> **R**OAMING_**CA**LL(*COD:CAL*, FOREIGN_CARRIER:CAR)
> 
> **P**ROMO_**CA**LL(*COD:CAL*, PROMO_TARIFF:P_TA)
> 
> **P**ROMO_**TA**RIFF(*TARIFF:TAR*)
> 
> **TOW**N(*TOWN*,NATION)
> 
> **CAR**RIER(*CARRIER*, NATION)
> 
> REQUESTS: 
> build a fact-schema for 'CALL' with following 
>
> dimensions:
> DATE, SIM_FROM, CALLED_CARRIER, FOREIGN_CARRIER, PROMO_TARIFF and
> 
> measures: AVG_CALL_LENGTH, NUM_OUTGOING_SIM (as count distinct FROM),
> NUM_INCOMING_SIM (as count distinct TO)

Now I can draw the fact-schema, but I'm in trouble finding what measures are aggregable along  which dimensions