PROSE is a knowledge-based configurator platform for telecommunications products. Its outstanding feature is a product knowledge base written in C-Classic, a frame-based knowledge representation system in the KL-ONE family of languages. It is the first successful product using a KL-ONE style language that we know of. Unlike previous configurator applications, the PROSE knowledge base is in a purely declarative form that provides developers with the ability to add knowledge quickly and consistently. The PROSE architecture is quite general and is not tied to any specific telecommunications product. As such, it is being reused to develop configurators for several different products. Finally, PROSE not only generates configurations from just a few high level parameters, but it can also verify configurations produced manually by customers, engineers, or sales people. The same product knowledge, encoded in C-Classic, supports both generation and verification of product configurations.