The looser your requirements are, the easier it is to write your own so-called database. Nobody should be writing a full ACID/SQL/whatever database as part of another project. On the other hand, if you want to implement a "database" in the same sense that many implement a "filesystem" which is just an HTTP object layer on top of a real filesystem, knock yourself out. Just don't think you're doing the same thing as the people writing more featureful general-purpose databases.