Applying metrics to software is a way to measure and improve software quality. Many metrics apply to software implementations (code), so they cannot be used early in the life cycle. We survey ten modularity and structural complexity metrics applicable to software designs, and summarize the results of empirical validation studies when they are available. We present a database schema from which most of these metrics can be computed. Aspects of each metric require further study and refinement. However, using some of them during design may still be beneficial.