The authors contend that it is both possible and necessary to clearly demark and explicitly define the transition between the software design and software implementation phases of the software life cycle. The output of the software design phase is defined to be a logical design of software, and the logical design can be described explicitly if the software is viewed as a system of data sets and data transforms. Logical Construction of Software (LCS) is a software design methodology that guides the designer in defining and describing these software components and their relationships. The methodology is illustrated via a practical application.