Start schema in relational database vs OLAP

I understand what OLAP and MOLAP are and their purpose in theory. Under what scenarios would one consider switching from start schemas in relational database to OLAP technology and building cubes? I understand this is more frequent in financial departments. Can one expand more about the usage? I understand it improves performance, but you can get pretty good performance by having star schemas in relational databses right?

And to move to OLAP technology, can you elaborate how it would be? Would I still populate the star schemas in relational databases and create cubes from there? Do you use an ETL tool for this?

If I have OLAP technology in our financial department, would I build a data warehouse in the same server?

Hello dellsters,

I think Ralph has a good article about this which may answer your questions about the advantages and disadvantages of both "worlds".
Take a look at http://kimballgroup.com/html/articles_search/articles2007/0704IE.html

Have a nice Day

Michael

Relational database structures are largely vendor independent and especially dimensional structures are pretty easily ported. However, ETL command line scripts and proprietary code like PL/SQL may not be very portable.You also check a book on OLAP.The book is available on Amazon & you can buy an e-book directly from the publisher by writing OLAPWorldPress@gmail.com.

Don't confuse OLAP with a particular physical database implementation. OLAP is a generic term referring to how one accesses and manipulates data. One can implement OLAP using relational databases, multidimensional databases, flat files, or Excel spreadsheets.

As the referenced article mentions, both relational and multidimensional database technologies have their advantages and disadvantages. From a data warehouse implementation standpoint, relational databases are the best (and probably only) choice. Data marts using multidimensional databases are often sourced from the DW and used in specific applications. They are often chosen for their performance and suitability to a particular use.

Has the industry been adapting dimensional relational as a general rule and only use OLAP when required, only for departmental solutions, when high performance is required?

Is anybody adapting the whole data warehouse/ BI be OLAP?

Once again, do not confuse OLAP (On-Line Analytical Processing) with database implementations. You can do OLAP with ANY data store, even flat files. The terms ROLAP, MOLAP and HOLAP do imply an implementation method, ie: relational, multidimensional and hybrid respectively. A hybrid implementaion uses multidimensional databases as its primary source with drill through capability to a detailed relational database. SQL Server is a good example of a hybrid environment that supports both relational and multidimensional data structures.

Pure multidimensional databases (such as Essbase, Cognos Powerplay etc...) are not suitable as a data warehouse platform because the way they store data limits them to summary data which is not what you want in a DW. Also, the query language (MDX) cannot 'join' cubes.