> A project needs to deliver simple functionality, dominated by data entry and display, with few business rules. Staff is not composed of advanced object modelers.
> [...] Simple projects come with short time lines and modest expectations. Long before the team completes the assigned task, much less demonstrates the exciting possibilities of its approach, the project will have been canceled. [...] And in the end, if they do surmount these challenges, they will have produced a simple system. Rich capabilities were never requested.
> Therefore, when circumstances warrant:
> Put all the business logic into the user interface. Chop the application into small functions and implement them as separate user interfaces, embedding the business rules into them. Use a relational database as a shared repository of the data. Use the most automated UI building and visual programming tools available.
> [...] Yet it is a legitimate pattern in some other contexts. In truth, there are advantages to the SMART UI, and there are situations where it works best—which partially accounts for why it is so common. Considering it here helps us understand why we need to separate application from domain and, importantly, when we might not want to.
> Advantages: Productivity is high and immediate for simple applications; Less capable developers can work this way with little training; Even deficiencies in requirements analysis can be overcome by releasing a prototype to users and then quickly changing the product to fit their requests; Applications are decoupled from each other, so that delivery schedules of small modules can be planned relatively accurately; Expanding the system with additional, simple behavior can be easy; Relational databases work well and provide integration at the data level; 4GL tools work well; When applications are handed off, maintenance programmers will be able to quickly redo portions they can’t figure out, because the effects of the changes should be localized to each particular UI.
> Disadvantages: Integration of applications is difficult except through the database; There is no reuse of behavior and no abstraction of the business problem. Business rules have to be duplicated in each operation to which they apply; Rapid prototyping and iteration reach a natural limit because the lack of abstraction limits refactoring options; Complexity buries you quickly, so the growth path is strictly toward additional simple applications. There is no graceful path to richer behavior.
> [...] Remember, one of the consequences of this pattern is that you can’t migrate to another design approach except by replacing entire applications. [...] Don’t bother hedging your bet. Just using a flexible language doesn’t create a flexible system, but it may well produce an expensive one.