Rule #9: Loosely couple the application code and the presentation code.

Loosely couple means helping other application programmers, user-interface programmers, and web designers stay out ofeach other's way.

Data Handling vs. Templating

An application programmer should not be required to master the user-interface DHTML, server-side script, or user-interface design concepts. Procedures that collect data from the back-end of the application should not template, or preformat, data with HTML prior to passing it to the client-side code. Data handling procedures should pass an unformatted collection to a separate templating procedures. Templating is the prerogative of the user-interface programmer. This way, the application programmer is relieved of maintenance caused by content or graphic design changes, and both can solve programming problems a little more independently of one another.

User-interface programmers should not be required to master the application or database logic. A web page should have access to server-side procedures that hand off data in a presentation-sensible way. If I want someone's username, I should be able to ask for username, even if it's really USRID_EN in the database. Application programmers should maintain the programs that receive client-side form postings. Those programs should handle reformatting data for storage in the system.

None of this prevents an individual developer from building skill with all tiers of the system. It does prevent that level of skill from becoming a requirement before a programmer can work productively.