contexts or alias

[Former Member]

when to use context method to resolve loops

and when to use alias method to resolve the loops?

yes, alias participate in contexts

[Former Member · Accepted solution]

Aliases should be used when the table you are considering using can serve two different purposes.

The most common example in data warehousing is the calendar table.

If you have a rental fact table and a sales fact table, you would create two aliases of the calendar table, one for rental date and one for sale date.

However, if you still have other conformed dimensions, such as salesperson (being a person who can sell and rent vehicles) then you will need to use a context. This is to avoid the chasm trap that you would otherwise encounter.This is covered in the designer pdf - chapter 4 - Resolving Join problems in a schema.

[Former Member · Accepted solution]

so can we say that the fact tables in the loop decides which method we have to use to resolve the loops.?????

Edited by: RohanGangil on Dec 24, 2010 11:51 AM

[Former Member · Accepted solution]

Partly.

The general rule of thumb is one context per fact table.

The detect context algorithm works by:

1/ identifying candidate tables with only many ends of joins attached to it (typically fact tables)

2/ following these joins out on all the many-one routes.

3/ suggesting these collections of joins as candidate contexts for you to add.

This method has the flaw that it doesn't "like" one-one joins, so you need to set these in the appropriate direction before you run the detect contexts functionality.

Contexts and aliases follow very simple rules and apply to whatever universe you work with (except SAP/OLAP universes where you don't need to manage the schema). Once you've understood them you'll be in a much better position to build universes with confidence.