On 24/12/10 00:07, Robert Houben wrote: > I've been watching this thread with some interest. Because I'm going to > reference our product, I'm putting th [AD] marker on this. > > One of our best-selling products assists our customers in rapid > migration/data warehousing of Multivalued and Subvalued data to either SQL > Server, Oracle, DB2, Progress, MySQL and other relational databases. > > We actually have a whole suite of tools to assist our customers in solving > these issues.
Except that's not the issue that the OP posed :-) He wanted to migrate AWAY from SQL server etc :-) > In order to go the other direction, there are some inescapable questions that > have to be answered: > > MV can only support 2 levels of nesting. If you have 3 or more 1-to-many > relationships, you have to decide at some point to keep a set of keys > (item-ids) in a multivalued or subvalued cross-reference and use another > file. Deciding where and when to do this becomes the tricky thing. > This, imho, is where the relational guys have a problem with reality. Yes I know that decision is HARD. So the relational guys abstract it away. The cost is that relational databases are not deterministic. It becomes a case of "yes there is definitely a solution, and I will definitely find it, but it may take longer than the life of the universe to get there" :-) (And I'm only *half* joking). THAT is the reason that MV engines are *always* faster than relational engines. Einstein said "don't make things *too* simple". The relational guys have done exactly that! > SQL uses indexes. MV uses cross references to item-ids (MV sometimes > supports indexes, but they don't always work as well as in the relational > world.) > I don't know as that is true ... or are you using the word "index" to mean something completely different to me? I'll agree the implementation of indices can be buggy, but surely that's true of relational engines too? > There are other issues, but that's a good starting point. If you really want > to explore the concept there is no substitute for playing with it, and you'll > discover there are more issues lurking there... Yup ... Cheers, Wol _______________________________________________ U2-Users mailing list [email protected] http://listserver.u2ug.org/mailman/listinfo/u2-users
