A tool for automatic extraction of logical structure from electrical description of a circuit, using frames as knowledge representation, is presented. The set of rules by means of with MOLD does its job is related to a Static CMOS logic, but every kind of technology (NMOS, Bipolar, etc. ) and design style (dynamic, precharged, etc. ) can be handled, just building up a proper set of rules. MOLD acts as an effective backtracing description tool, being able to update a higher level description as a consequence of changes in the lower one. MOLD shows advantages in computation time compared with algorithmic approaches.