A simple formal framework for representing safety and progress properties of concurrent systems is introduced. The framework is based on Enhanced Characteristic Functions (ECF), which lead to simple definitions of operations such as hiding and process product. Two distinct compositions are proposed: The network composition that models networks of devices, and the specification composition that enables a constraint-based approach to building specifications. A part-wise design and verification approach is proposed. This approach may avoid state explosion in the verification of implementations for constraint-based specifications.