SAP BW is a very large scale datawarehousing tool based on ROLAP
technology.It has its own reporting Tool - BEX and its own star
schemas and ROLAP based cubes.
Cognos Powerplay is an OLAP based system , that sits on top of a
Star schema.
the SAP BW system has more overall functionality than the Cognos
system in terms of database schemas and extraction
transformation and loading.
One of the fundamental differences between SAP BW and Cognos is
in the ROLAP and OLAP technologies they base their cubes on.
The SAP BW Rolap is a relational database based on Oracle or DB2
or Microsoft Sql server.
the Cognos OLAP cubes are based on compressed large binary
objects.
This difference leads to the SAP BW system having the advantage
that the extract and data load time to the ROLAP level is as
fast as any good database load/insert can be and in theory this
is the only load time that you will incurr.
For the equivalent Cognos based system you may (if you are
running a data warehouse level)need to load your daily/weekly
data into a star schema and then subsequently load this data
into a Powerplay cube .
The load of the data intto the Powerplay transformer engine and
the subsequent creation of the Powerplay cube binary object -
can take a long period of time.This depends on the number of
rows you are loading and the parallel nature of the queries and
the complexity of the cube design.
So, for very large multi terrabyte systems, you may encounter
difficulties in fitting all the Powerplay cube creations into
your batch window.
However, SAP Bw has a similar problem i that it normall relies on
a level above the ROLAP, called Aggregations - and these are
similar in result to the Powerplay cubes aggregations - except
the BW ones are held in DB2 or Oracle and the powerplay ones are
Blobs.
Powerplay has better graphing and time series functionality - the
graphs are embedded in the Powerplay functinality - whereas in
SAP bW the graphs tend to be stuck on top of the spreadsheet
output.
I would say in summary, that the Cognos Powerplay system is
easier to use and deploy than SAP BW, but SAP BW is possibly
better for the complete end to end data warehouse solution - but
doesnt look quite as nice as Cognos to the end users.
