The relational model, as implemented in many database management systems, has many positive attributes but fluidity is not one of them.
The temporalists: point to the weakness of the relational model when it comes to one of the most frequent concerns in IT systems. Namely, how information changes over time. Although the time dimension can be factored into relational systems, it is not something that the model itself promotes. In fact, it can be argued that relational data normalization is antithetical to the common requirement of capturing “point in time” views of a business process or a corpus of content.
The rise of the hierarchicalists
XML, like SGML before it, takes the view that much information is naturally hierarchical in form. SGML never really caught on outside of some niche areas but XML – its successor – is slowly but surely carving out a following in the mainsteam database management arena. For all its faults, the W3C XML Schema Language (XSD
) is one reason for this but I think it is XQuery
that is really responsible for the shift to center stage. Not many technologists under the age of, say, forty will remember but believe it or not, there was life in the field of hierarchical database management long SGML and XML came along in the form of IMS
. It can be argued that technology and adoption are really just catching up with an idea that is now over forty years old.
The intriguing thing about XQuery is that it sets out not so much to kill the relational database but more to extend it. It does this in the time honored way of treating the enemy as a mere special case of a more powerful data modelling abstraction. I.e. to the hierarchicalists, relational tables are merely very regular, shallow and non-recursive hierarchies.