The new menagerie of NoSQL databases do not have the same characteristics as traditional SQL databases, much less each other. Which is kind of the point of using them in the first place.
So why are so many otherwise sane and smart people doing their best to ignore this fact? And why is the middleware community pandering to their delusions?
There is a dangerously seductive attraction in the idea that you can improve an existing system just by swapping out some component implementation for another using the same interface. A java.util.Map may abstract a Hashtable, HashMap, ConcurrentHashMap or distributed, replicated in-memory data grid like Infinispan. Choose wisely and your system works better. Choose poorly and things unravel pretty fast. It is necessary to look beyond the interface to the underlying implementation and understand the details in order to know how to drive the interface in optimal, or even correct, manner.
The JPA may abstract not only one of several ORMs, but one of an even larger number of relational database engines behind them. It may even be implemented using an OGM backed by a key-value store such as Infinispan or Cassandra. The ability to reuse existing JPA code or programming skills when migrating from relational to non-relational storage is attractive to both developers and management. The middleware community responds to this user demand with solutions like Kundera and Hibernate OGM, which developers lap up in ever increasing numbers. Unfortunately they often do this with an inadequate understanding of the underlying implementation details.
As middleware developers we are guilty of doing too good a job of abstracting away the underlying implementation detail. Many users willingly buy into this delusion, being all too keen to believe we can magically shield them from having to understand those details.
There are two approaches to dealing with this problem: Improve the abstraction so it becomes less important to understand the implementation details, and provide material to help the users understand those details in cases where they must.
These tasks are going to occupy a big chunk of my time in the future, as I shift attention towards providing transaction management capability for the new generation of cloud environments, where data is managed and manipulated in both SQL and NoSQL stores. Interesting times ahead I think.