Specifying Systems

TLA+ represents an effective methodology for visualizing and quantifying algorithmic complexity in a way that is meaningful to engineers.

"TLA+ represents the only effective methodology I've seen for visualizing and quantifying algorithmic complexity in a way that is meaningful to engineers."
--Brannon Batson, Processor Architect, Intel Corporation

This long-awaited book shows how to write unambiguous specifications of complex computer systems.

The first part provides a concise and lucid introduction to specification, explaining how to describe, with mathematical precision, the behavioral properties of a system--what that system is allowed to do. The emphasis here is on safety properties.

The second part of the book covers more advanced topics, including liveness and fairness, real-time properties, and composition.

The book's final two parts provide a complete reference manual for the TLA+ language and tools, as well as a handy mini-manual. TLA+ is the language developed by the author for writing simple and elegant specifications of algorithms and protocols and for verifying the correctness of a design. The language already has proved to be a valuable aid in understanding and building concurrent and distributed systems. Tools for TLA+ syntax analysis and model checking are freely available from the Web, where you can also find supplemental materials for this book, including exercises.

This book is the distillation of over 25 years of work by one of the world's most renowned computer scientists. A specification is a written description of what a system is supposed to do, plus a way of checking to make sure that it works. Specifying a system helps us understand it. It's a good idea to understand a system before building it, so it's a good idea to write a specification of a system before implementing it. The most effective tool to describe a specification is the Temporal Logic of Actions, or TLA, because it provides a mathematical, i.e. precise, foundation for describing systems. TLA+ is the language the author developed to write the mathematical specifications. TLA+ is available freely on the web. It can be used for both software and hardware. In fact, Intel is using TLA+ with great success in the design of a new chip. The book is divided into four parts. The first part contains all that most programmers and engineers need to know about writing specifications. The second part contains more advanced material for more sophisticated readers. The third and fourth parts comprise a reference manual for TLA+ - both the language itself as well as its tools.