State Management

I was expecting good things from the Ted Neward presentation to the SDForum Software Architecture and Modeling SIG, and I was not disappointed. The presentation was titled "State Management: Shape and Storage: The insidious and slippery problem of storing objects to disk".

However I have to say that the presentation did not go in the direction I expected. Ted started out by drawing the distinction between Transient state and Durable state, where Durable state is the set of objects that reside in a database. He made a passing reference to transient objects becoming durable and I was expecting him to talk about whether durable objects should be distinct from transient objects or whether an object can morph from transient to durable and back again, but he did not go there. He did spend some time on the problem of object management on a clusters. For most of the audience this was preaching to the choir.

Next Ted talked about the shape of durable data: Relational, Object or Hierarchical. We all know the object and relational shapes, and the difficulty of mapping between them. XML is hierarchical data. Ted spent some time convincing us that hierarchical data is not the same shape as object data, the two are different and there is no easy mapping from one to the other. This was the piece of the talk that I found most interesting and he certainly convinced me. After the meeting I want back and looked at my copy of Date (2nd edition, 1977) which has it all. Date describes the three shapes of data: Relational (Relational) , Hierarchical (XML) and Network (Object). Note that Date took the Hierarchical and Network stuff out of later editions.

Finally Ted referred to his controversial blog post on "Object/Relational Mapping is the Vietnam of Computer Science". His argument is that early success with Object Relational mapping has got us on a slippery slope to a morass from which there will be no easy escape. Go read the original, which is better than any summary that I could write here. I agree with him and I will put more thoughts related to this topic in future posts.