Yes, for example, in MongoDB you do not have unions, because it is non-relational , so it changes the way you store and view data.
MongoDB ( ), ( " " ) . MongoDB: -, DBRef, .
, , , , .
, ( SO , , ). , "" , . .
. :
GAE - ?
API, Google BigTable nosql? (- Hibernate)
JDO datastore-agnostic, , .
, JDO JPA "NoSQL".
:
Datanucleus-Cassandra
Datanucleus-Cassandra-Plugin