universes are 3 types : 1)simple universe
2)complex universe 3)dervied universe

 In metric universe aggregate summary is disable. so metric 
universe is not used
in simple uni while the aggregate summary is enable. and 
also it generates the summary.

at 3rd question i dont know.

There is only one universe in terminology of BO, but there 
may be many situations based on the usage, where we can 
classify the universes as-

1. Depending on type of data universe objects mapping

a.	Ad-hoc (personal data) – The Universe created for a 
personal usage is called Ad-hoc Universe and these are not 
shared with anybody else.
The reports created using these universes are called Ad-hoc 
Reports and generally users have the rights to store the 
reports in the Inbox. Ad-hoc reporting is a user friendly 
feature designed for all levels of users. Custom reports 
are created using queries.
b.	Non Ad-hoc (corporate data) – The universe created 
for a corporate usage is known as Non ad-hoc Universe these 
are sharable Universes and reports created from these can 
be viewed by all the users.

2. In linking universes scenario
a.	Core universe (Kernel or Master universe) – The 
Universe created and used with another universes for the 
reusability of the components.
b.	Derived universe – The Universe created using Core 
universe and there own required components.

3. Depending on universe parameters.
a.	Secured universe.
b.	Personal universe.
c.	Shared universe.