When you have multiple fact tables then we have to go for 
Contexts, there is no othergo. In the other situations we 
can use aliases.

We use alias or context wenever we encounter a loop .If 
there are more than one fact table use a context or if only 
one fact table use alias

Alias,contexr these two we can used to resolve join 
problems.whemn we found a loop in our scheema design we 
will go for alias,when we are able to run two sql 
statements as a single query we go for contexts.

we have option for these in our universe tool bar window

tools-->auto detection--.context or loop