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Message Posted: Wed, 19 Dec 2001 @ 18:16:50 GMT
I have seen the big bang tried and fail, more than once, so wholeheartedly support the gradual or evolutionary approach.
The business objective should be the driver.
I am not sure what you mean by "merge" - will the Oracle DW continue and what for? Perhaps, some business data analysts will continue to use Oracle for OLAP views of (some of) the data? If so, let them continue as before but, behind the scenes, load source data to Teradata and then replace the feed from source to Oracle by a feed from Teradata to Oracle. That achieves the "one truth" concept without rocking business functionality.
If the business data analysts who currently access Teradata need to quickly see data regarding the additional business together with the original business, copy tables from Oracle to Teradata for them. Then, behind the scenes, load from source to Teradata and develop replication of the processing currently undertaken in Oracle to test before switching off the Oracle DW.
One key point is the amount of history and the granularity that the combined business may want about the old business - check asap and secure the relevant tapes or even load to Teradata ahead of defining the new enterprise data model.
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