Omega is a logic system for knowledge representation which is based on descriptions, rather than predicates, and embodies two fundamental ideas for structuring knowledge that are distilled from semantic networks and frame based languages: inheritance and attributions. These features can be exploited to build knowledge bases organized as networks of descriptions, where all types of knowlegde are uniformly represented in an integrated fashion. Reasoning on a lattice of descriptions combined with deduction strategies defined at the metalevel provide the knowlegde base with the capability to deal with complex problem solving tasks.