Abstract: The cost of correcting or remedying errors would increase by geometric series at the later of software development.Thus the quality of formal specifications becomes one of the key issues and difficulties.But little work has been done on how to measure the quality of formal specifications till now.To solve these problems, a suite of metrics to measure schemas of formal specification language Z is proposed.The metrics consider schema decoration, schema inclusion, schema type, and schema calculus.According to these metrics, some problems can be found and further overcome at the early life cycle, which reduce cost greatly.Besides, an effective estimation of the system can be made.

Key words: formal specification language, schema, Z, software measure