Why dont people simply use "Object Database"s?

Instead of JDO , Hibernate , iBATIS why we can not simply use "Object DataBases" ?

http://en.wikipedia.org/wiki/Comparison_of_obj开发者_Python百科ect_database_management_systems

Even if these object databases would sometimes suffer to store and retrieve the data for an application, most of the time there are other edge conditions:

• You already have an installed relational db and hired an admin for it.
• You need programs like Crystal Reports to do some stuff with your data.
• You don't want to rely on a database that isn't as widespread as a relational one.

The reason is clearly laid out here by Mark Harrison amongst others. In short, relational DBs have historical momentum, and are technically superior for a lot of stuff. Also relational DBs just work better, at least in 2009 (check out the other answers to the question I referenced).

At the same time, you do need JDO, ActiveRecord, or something to avoid writing standard object-DB translations yourself.

Because most developers do not know enough, most of customers already have an installed relational db and hired an admin for it and best of them are quite specific and commercial. Here you are one suitable database benchmark to test and see result of work on most famous DMS

Because objects are all about hiding data and databases are all about making data public.

From that point of view, one could even say that "an OO dbms" is a contradiction of terms.