When to use Change dimension activity?

[god_prophet]

I have these cases from the preparation test and I need your help understanding "Change dimension activity".

1.- The business practicioner wants to obtain the total travel miles per recipient. Two different sets of data neeed to be combined in order to target/analyze that:

A) The first set of data contains recipient's personal info from Recipient schema.
B) The second set of data contains travel miles from the Travel schema.

The answer is: A change dimension activity is needed before merging the information in either the Travel or Recipient schemas.

At first I thought a "change dimension activity was needed because, according to the question, those tables were not linked.But in the documentation, here, it shows it is used for linked schemas?

2) In this other question, were tables are not linked, why the answer doesn't involve a Change dimension activity?

"An Adobe Campaign business practicioner is building a workflow and has been asked to use two internal Adobe Campaign schemas (tables are not linked):

A) Clients table

B) Contract Holder Table

The consultant need to select clients who have had a life-insurance policy for over 5 years. 

Which statement is true regarding the decision to choose the correct filtering and targeting dimension in Query Activity?

Using a Changing dimension activity would have been possible for this case? 

[_Manoj_Kumar_ · Accepted solution]

@god_prophet 

I have posted the answer here: Solved: Re: Confused with targeting and filtering dimentio... - Adobe Experience League Community - ...

[vt0509]

Hi @god_prophet,

In the first case, a change dimension will be used if you select Travel schema as the "Targeting Dimension" while creating your query. Change dimension can be used for linked tables when you need to change the dimension from Travel schema to Recipients.

In the second case, as there is no linking between tables, you wont be able to do a change dimension. You have to link the tables to query the desired output. Dimension can be changed with the help of Reconciliation (in Enrichment).