[marktangotango]

You are correct, the parent made a broad generalization that's not true. Mongodb indexes represent the sitaution though, in a schemaless environment, what is the meaning of an index on a collection heterogenuous records? If the system enforces that the indexed fields are always present (either the app or the nosql store) then hmmm isn't that a schema?

The other issues is joins across record types sometimes joins are supported, sometimes not.