 <p>There are a lot of other conditions that I've been hearing about with non-relational systems vs relational. I prefer this terminology over sql/no-sql as I personally think it describes the differences better, and several of the "no-sql" servers have sql add-ons, so anyway.... what sort of concurrency pattern or tranaction isolation is required in your system. One of the purported differences between rel and non-rel dbs is the "consistent-always", "consistent-mostly" or "consistent-eventually". Relation dbs by default usually fall into the "consistent-mostly" category and with some work, and a whole lot of locking and race conditions, ;) can be "consistent-always" so everyone is always looking at the most correct representation of a given piece of data. Most of what I've read/heard about non-rel dbs is that they are mainly "consistent-eventually". By this it means that there may be many instances of our data floating around, so user "A" may see that we have 92 widgets in inventory, whereas user "B" may see 79, and they may not get reconciled until someone actually goes to pull stuff from the warehouse. Another issue is mutability of data, how often does it need to be updated? The particular non-rel db's I've been exposed to have more overhead for updates, some of them having to regenerate the entire dataset to incorporate any updates.</p> <p>Now mind, I think non-rel/nosql are great tools if they really match your use case. I've got several I'm looking into now for projects I've got. But you've got to look at all the trade offs when making the decision, otherwise it just turns into more resume driven development.</p>