[axelf]

wouldn't a single abstraction over postgres, filesystem, hadoop, etc be either really leaky or really inefficient? different datastores are better suited for certain kinds of queries. It seems like the programmer should be aware of what he/she is querying.

[kasey_junk]

You invert the dependency. The abstraction is over the things that the higher level code needs. I don't need to know about query types, indexes etc. I need some business answer (all log records between x/y, a user matching username x), I program to an interface that provides all the answers necessary for the high level code.

The implementation of that interface is data store aware and implements the interface in the most effective way possible for the data store holding the things I'm interested in.