What is best way to best way to migrate data from one product to another if both software companies refuse to reveal the database structure to one another?
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38answers:
4morse code? smoke signals? braille?
really, it sounds like an untenable situation between two parties that have no confidence in once another and sounds poisonous.
dump the data to a csv and hand it to the other company. A good DBA can take the data and write a sufficient import script that maps them to the correct datatypes on the other end.
Define some database structure capable of holding all the relevant information (it doesn't need to be optimized in any way), have the first company dump their data into that and the second one import it.
Holy smoke. Sounds like great fun of yours ;-).
Just some ideas:
If you have access to the database... for a good dba the migration should be no problem at all.
Another way would be that one company creates views to hide the underlaying datastructures and the other company can import those views.
Otherwise just let them dump the data into flat files and import those files.