"As many relational databases such as MySQL do not have native support for inheritance this concept is approximated by joining normalised tables which together

"As many relational databases such as MySQL do not have native support for inheritance this concept is approximated by joining normalised tables which together have all the attributes necessary to build a subclass object." This suggests to me that their problem is not JOIN but a dogged insistence on a particular style of object-relational mapping. If you're having to do complex joins to retrieve a single persisted object you're probably coupling your objects and the database too closely. That said, a customizable CMS is a natural fit for both document databases and graph databases. All of the ones I've seen built on relational DBs have extremely generic schemas that allow users to build their own quasi-schemas on the fly, at which point you've sacrificed pretty much every benefit the relational model brings.