i'm new to dw been to oltp for some time

I'm new to dw i'm just confuse with the terms
1. what is a warehouse?
Is it just a copy of an OLTP database that has been cleased and transformed
is this a SQL server DB and not an AS DB
or is it the AS DB
thanks
Jose de Jesus Jr. Mcp,Mcdba
Data Architect
Sykes Asia (Manila philippines)
MCP #2324787
Before explaining a data warehouse you need to think of the
opposite, a transaction system. If your company sells things
then you will likely have a transaction system which stores
details of all your customers, what they have bought, how
much they owe, what products you are selling etc.
But this transaction system is ever changing, and it is almost
impossible to find out if, for example, you are selling more this
month that you did last month, or if you are owed more money
this month than last month, or if the sales of a certain product
has increased because of the marketing campaign you ran in
the north for the last three months.
So with a data warehouse you take a 'snapshot' of the data at
a particular time:- hourly, daily, weekly, monthly etc. Gradually
you build up a history of what was in your transaction database
and you can then perform 'business intelligence' on that data to
try to help you run your company better.
This business intelligence is done with 'query and reporting' tools
of which there are many, but products such as Excel, Access, Brio,
Business Objects, Crystal Reports, Cognos etc can all be used.
You can also aggregate and summarize the data as you go along,
so that users do not see all the detail, but just a summary of all
the products sold in the north, or the west and so on.
Of course you store this data warehouse on a different machine,
and in a different relational database server. This is because you
do not want to impact the performance of your transaction system
when people are doing end-user queries on the data warehouse.
Now the hard part is deciding what data to put in your data
warehouse, how often to put it there, even finding out what all
your data means (many companies do not actually know what
all the data in their database means).
Of cours you can also build an OLAP cube, which is a form of
a data warehouse. Here all the data is pre-aggregated to produce
very fast query results, but of course you can only query what is
in the 'cube'.
In SQL Server an OLAP cube is held in relational tables (fact tables
and dimensions tables) but you do not query the tables directly
but via the 'cube'. Some products, such as Hyperion Essbase, do not
hold their cube in relational tables.
Building a data warehouse or OLAP cube, can be a long and
complex job (just finding out what data a company has, where it
is, and how to access it, can be a major job).
There are plenty of books about data warehouse if you look
for them
Alan
|||Hi Jose,
I have published a lot of materials for 'newbies' on my personal
website www.peternolan.com. If you have anything else you would like
to see on my website please let me know as I am always interested in
hearing feedback on what is there.
By the way, I notice you are in Manila. I used to work with Remax
International and they are great people. You might want to call them
and see if they can come and present to your company about BI/DW...I
could not find their web site...I did find
this..http://www.celerant.com/Internationa...ssPartners.cfm
Remax was in Makati district..I'm sure you will be able to find them in
your local web sites or phone books...
Best Regards
Peter Nolan...