A method for designing and prototyping program construction systems using relational databases is presented. Relations are the only data structures used inside the systems and for interfaces; programs extensively use relational languages, in particular relational algebra. Two large projects are described. The Ada Relational Translator (ART) is an experimental compiler-interpreter for Ada in which all subsystems, including the parser, semantic analyzer, interpreter, kernel, and debugger, use relations as their only data structure; the relational approach has been pushed to the utmost to achieve fast prototyping in a student environment. Multi-Micro Line (MML) is a tool set for constructing programs for multimicroprocessors’ targets, in which relations are used for allocation and configuration control. Both experiences confirm the validity of the approach for managing teamwork in evolving projects, identify areas where this approach is appropriate, and raise critical issues.