On Aug 22, 1:40 am, "Jeje" <willg...@hotmail.com> wrote:
> SSAS 2005 like any other OLAP tool on the market can works with flat schemas
> and more complicated schemas.
>
> but using star or snowflake schema is far better for a DW project and when
> you create a cube.
> SSAS 2005 is able to create the tables for you, so instead of creating the
> tables in the database then creating the cube, you create your dimensions
> and cubes first and SSAS2005 will generates the tables for you.
> this greatly simplify the prototype step of your project.
>
> proactive caching don't switch from MOLAP to ROLAP.
> proactive caching can detect changes in the source database and then update
> the cube automatically or can do an incremental loading automatically.
> there is a lot of options available here for different usage and
> requirements.
> but there is no switch from MOLAP to ROLAP.
>
> the ETL process is not required if your cubes are directly connect to the
> operational database.
> today, a lot of databases schemas are more accessible then before and the
> data quality is good, so accessing the source database is a good option.
> it's also a good option when you have only 1 database to play with (and not
> a lot of databases to synchronize)
> but if you have to sync. multiple databases, or you have to do a lot of
> cleansing / transformations, then an ETL process is required.
> another option we can found today:
> the transaction made to the operational system are also replicated into the
> datawarehouse in real time (using triggers, procedures or workflow systems)
> so the DW database himself become a realtime system.
>
> "Nestor" <n35...@yahoo.com> wrote in message
>
> newsp.txe6yasa83lx0t@david.virginam.com...
>
>
>
> > Hi everyone,
>
> > I have a general question to datawarehousing and it'll be great if someone
> > can drop some tips here. I'm about to start designing a corporate real
> > time datawarehouse with SQL Server 2005 and is deciding on the approach
> > for this.
>
> > SQL Server 2005 now allows us to actually build a datawarehouse without
> > actually restructuring the datasources into star/snowflake schemas. I'm
> > curious to know if this will have any performance impact on the actual
> > implementation? This project will probably require the usage of proactive
> > caching as well as medium latency molap storage structure.
>
> > By using proactive caching, SSAS will intelligently switch between ROLAP
> > and MOLAP depending on the data changes in the production database. What
> > is confusing to me is, what happens to ETL then? Does this mean that if
> > SSAS is made to query directly from the production database, then ETL is
> > totally eliminated?
>
> > Any recommendations will be appreciated.
>
> > Thanks.
> > Nes- Hide quoted text -
>
> - Show quoted text -

I would add that in my experience creating a set of views to replace
the star schema is good only for prototypes. Chances are that in a
real world environment you need to do some transformation and/or
cleansing operations that requires you having some staging/working
area. Moreover, you will have a longer lifetime of your solution if
you decouple your OLTP source from the db that becomes the physical
OLAP Data Source.

The capability of SSAS to handle relationship more complex than star/
snowflake schema is a tentative to reach the "UDM utopia" (UDM means
Unified Dimensional Model, at the beginning of Yukon story it was the
"final" model on which every report will be based on - but just only
SSRS has a different model from UDM, so we are still far from
realizing this vision). Today, I'm very happy to use UDM as an OLAP
model that is much richer than those offered by other products (the
single feature of many-to-many dimension relationships allowed me to
build a lot of complex analytical models, like I described in my paper
- http://www.sqlbi.eu/manytomany.aspx).

Marco Russo
http://www.sqlbi.eu
http://sqlblog.com/blogs/marco_russo