What are the different Lookup methods used in Informatica?

connected lookup will receive input from the pipeline and sends output to the pipeline and can return any number of values.it does not contain retun port .
Unconnected lookup can return only one column. it containn return port. 


can we lookup a table from source qualifier transformation. ie. unconnected lookup

You cannot lookup from a source qualifier directly. However, you can override the SQL in the source qualifier to join with the lookup table to perform the lookup.


what is ODS (operation data source)

ODS is the Operational Data Source which is also called transactional data ODS is the source of a warehouse. Data from ODs is staged, transformed and then moved to datawarehouse.


what is the difference between etl tool and olap tools

ETL tool is ment for extraction data from the legecy systems and load into specified data base with some process of cleansing data.

ex: Informatica,data stage ….etc

OLAP is ment for Reporting purpose.in OLAP data avaliable in Mulitidimectional model. so that u can write smple query to extract data fro the data base.ex: Businee objects,Cognos….etc