No silver domain modeling bullets
This past week, I attended a presentation on Object-Role Modeling (with the unfortunate acronym ORM) and its application to DDD modeling”. The talk itself was interesting, but more interesting were some of the questions from the audience. The gist of the tool is to provide a better modeling tool for domain modeling than traditional ERM tools or UML class diagrams. ORM is a tool for fact-based analysis of informational models, information being data plus semantics. I’m not an ORM expert, but there are plenty of resources on the web.
One of the outputs of this tool could be a complete database, with all constraints, relationships, tables, columns and whatnot built and enforced. However, the speaker, Josh Arnold, mentioned repeatedly that it was not a good idea to do so, or at least it doesn’t scale at all. It could be used as a starting point, but that’s about it.
Several times at the end of the talk, the question came up, “can I use this to generate my domain model” or “database”. Tool-generated applications are a lofty, but extremely flawed goal. Code generation is interesting as a one-time, one-way affair. But beyond that, code generation does not work. We’ve seen it time and time again. Even though the tools get better, the underlying invalid assumption does not change.
The fundamental problem is that visual code design tools can never and will never be as expressive, flexible and powerful as actual code. There will always be a mismatch here, and it is a fool’s errand to try to build anything more. Instead, the ORM tool looked quite useful as a modeling tool for generating conversation and validating assumptions about their domain, rather than a domain model builder.
Ultimately, the only validation that our domain is correct is the working code. There is no silver bullet for writing code, as there is always some level of complexity in our applications that requires customization. And there’s nothing that codegen tools hate more than modification of the generated code However, I’m open to the idea that I’m wrong here, and I would love to be shown otherwise.