What is a formal method

A formal method is a mathematically-based technique used in Computer Science to describe properties of hardware and/or software systems. It provides a framework within which large, complex systems may be specified, developed, and verified in a systematic rather than ad hoc manner. A method is formal if it has a sound mathematical basis, typically given by a formal specification language. A formal method is only a method, rather than an isolated mathematical entity in itself, because of a number of pragmatic considerations: who uses it, what it is used for, when it is used, and how it is used This paper elaborates on what makes up a formal method and compares six different well-known formal methods, three used to specify abstract data types and three used to specify properties of concurrent and distributed systems.