One of the most often mentioned issues reported by software engineers working with relational databases from object-oriented languages is the object-relational impedance mismatch. Document databases adopters are saying that one benefit of document stores is that there is no impedance mismatch between the object and document worlds.
I don’t think this is entirely true.
Firstly, the numerous object-document mapping frameworks are a proof people are still using tools to convert between objects and documents. CouchDB and MongoDB already have many mapping frameworks available in the most popular languages.
Secondly, if you consider the highly connected hierarchical object model you’ll realize that mapping it into the document model is not consistent. It requires applying specific domain knowledge and involves different strategies depending on usage scenarios.
So, what is my point? Document databases are not solving the impedance mismatch with the object world. All they do is offering more flexibility in converting from one to another.
Original title and link: Document Databases and the Impedance Mismatch with the Object World (NoSQL databases © myNoSQL)