The following reasons come to mind wrt RDBMS: - When properly normalized, future modifications to the relational model will often be much simpler. Transforming

The following reasons come to mind wrt RDBMS: - When properly normalized, future modifications to the relational model will often be much simpler. Transforming hierarchical data stores or document-based ones often involves changing much of the code which calls the database - Query optimizers are often performing work which is difficult to implement yourself. - When properly called, query composition allows more computation to be done close to the data. - Knowledge of RDBMs is widespread allowing a low barrier to entry (is also a huge disadvantage, since it brings inexperienced people to use a sophisticated tool, leading to overgeneralized bad press) - Index management in relational model is often simpler and logical - Many RDBMs have a proven track-record of stability, code quality and feature completeness. Take a look at PostgreSQL, for example: GIN / GIST / PostGIS / date-time / windowing functions / streaming results. Also, the extensibility of postgres is astonishing, the community is warm and welcoming to beginners. Obviously, I could make a similar list of disadvantages of RDBMs. It's just my experience that the advantages mostly outweigh the disadvantages.