I've been reading the advantages and disadvantages of EAV model. Although, EAV provides great flexibility in adding new attributes, there are some issues when you do DMLs or do complex queries. Although, there are alternatives to EAV model, such as XML DB and object oriented databases, but I do not know if XML DB is better than EAV or comparable in performance to conventional DBs. Are there any real world cases of using XML DB somwhere? What about patient records applications, is there any successfull implementations of XML DBs for such applications?