Maude system

Last updated

The Maude system is an implementation of rewriting logic. It is similar in its general approach to Joseph Goguen's OBJ3 implementation of equational logic, but based on rewriting logic rather than order-sorted equational logic, and with a heavy emphasis on powerful metaprogramming based on reflection.

Contents

Maude is free software, and tutorials are available online. It was originally developed at SRI International, [1] but is now developed by a diverse collaboration of researchers. [2]

Introduction

Maude sets out to solve a different set of problems than ordinary imperative languages like C, Java or Perl. It is a formal reasoning tool, which can help us verify that things are "as they should", and show us why they are not if this is the case. In other words, Maude lets us define formally what we mean by some concept in a very abstract manner (not concerning ourselves with how the structure is internally represented and so on), but we can describe what is thought to be the equal concerning our theory (equations) and what state changes it can go through (rewrite rules).

Maude modules (rewrite theories) consist of a term-language plus sets of equations and rewrite-rules. Terms in a rewrite theory are constructed using operators (functions taking 0 or more arguments of some sort, which return a term of a specific sort). Operators taking 0 arguments are considered constants, and one constructs their term-language by these simple constructs. Maude lets the user specify whether or not operators are infix, postfix or prefix (default), this is done using underscores as place fillers for the input terms.

Reduction equations are assumed to be confluent and terminating. Rewrite rules do not have this restriction.

When Maude "executes", it rewrites terms according to the equations and rewrite rules. Maude rewrites terms according to the equations whenever there is a match between the closed terms that one tries to rewrite (or reduce) and the left hand side of an equation in our equation-set. A match in this context is a substitution of the variables in the left hand side of an equation which leaves it identical to the term that one tries to rewrite/reduce. Equations and rewrite rules can also be conditional rules, which means they have to fulfill some criteria to be applied to the term (other than just matching the left hand side of the rewrite rule).

The rules are applied at "random" by the Maude system, meaning that you can not be sure that one rule is applied before another rule and so on. If an equation can be applied to the term, it will always be applied before any rewrite rule. Maude's built-in search can look for unwanted states and show that no such states can be reached. Maude has the ability to control what rule applications should be attempted at each step using meta-programming, due to the reflective property or rewriting logic.

Usage

Maude has been used to validate security protocols and critical code. The Maude system has proved flaws in cryptography protocols by just specifying what the system can do, and by looking for unwanted situations (states or terms that should not be possible to reach) the protocol can be shown to contain bugs, not programming bugs but situations happen that are hard to predict just by walking down the "happy path" as most developers do.

Related Research Articles

<span class="mw-page-title-main">Discrete mathematics</span> Study of discrete mathematical structures

Discrete mathematics is the study of mathematical structures that can be considered "discrete" rather than "continuous". Objects studied in discrete mathematics include integers, graphs, and statements in logic. By contrast, discrete mathematics excludes topics in "continuous mathematics" such as real numbers, calculus or Euclidean geometry. Discrete objects can often be enumerated by integers; more formally, discrete mathematics has been characterized as the branch of mathematics dealing with countable sets. However, there is no exact definition of the term "discrete mathematics".

A relational database is a database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relational database systems are equipped with the option of using the SQL for querying and maintaining the database.

In logic and computer science, unification is an algorithmic process of solving equations between symbolic expressions.

In computer science, Backus–Naur form or Backus normal form (BNF) is a metasyntax notation for context-free grammars, often used to describe the syntax of languages used in computing, such as computer programming languages, document formats, instruction sets and communication protocols. It is applied wherever exact descriptions of languages are needed: for instance, in official language specifications, in manuals, and in textbooks on programming language theory.

In computer science, formal methods are mathematically rigorous techniques for the specification, development, and verification of software and hardware systems. The use of formal methods for software and hardware design is motivated by the expectation that, as in other engineering disciplines, performing appropriate mathematical analysis can contribute to the reliability and robustness of a design.

In mathematics, computer science, and logic, rewriting covers a wide range of methods of replacing subterms of a formula with other terms. Such methods may be achieved by rewriting systems. In their most basic form, they consist of a set of objects, plus relations on how to transform those objects.

The Knuth–Bendix completion algorithm is a semi-decision algorithm for transforming a set of equations into a confluent term rewriting system. When the algorithm succeeds, it effectively solves the word problem for the specified algebra.

OBJ is a programming language family introduced by Joseph Goguen in 1976, and further worked on by Jose Meseguer.

In computer science, graph transformation, or graph rewriting, concerns the technique of creating a new graph out of an original graph algorithmically. It has numerous applications, ranging from software engineering to layout algorithms and picture generation.

<span class="mw-page-title-main">Confluence (abstract rewriting)</span>

In computer science, confluence is a property of rewriting systems, describing which terms in such a system can be rewritten in more than one way, to yield the same result. This article describes the properties in the most abstract setting of an abstract rewriting system.

In mathematics, computer science and logic, overlap, as a property of the reduction rules in term rewriting system, describes a situation where a number of different reduction rules specify potentially contradictory ways of reducing a reducible expression, also known as a redex, within a term.

The Abstract Rewriting Machine (ARM) is a virtual machine which implements term rewriting for minimal term rewriting systems.

John Vivian Tucker is a British computer scientist and expert on computability theory, also known as recursion theory. Computability theory is about what can and cannot be computed by people and machines. His work has focused on generalising the classical theory to deal with all forms of discrete/digital and continuous/analogue data; and on using the generalisations as formal methods for system design; based on abstract data types and on the interface between algorithms and physical equipment.

In mathematical logic, a term denotes a mathematical object while a formula denotes a mathematical fact. In particular, terms appear as components of a formula. This is analogous to natural language, where a noun phrase refers to an object and a whole sentence refers to a fact.

The following outline is provided as an overview of and topical guide to formal science:

In computer science, algebraic semantics is a form of axiomatic semantics based on algebraic laws for describing and reasoning about program specifications in a formal manner.

In rewriting, a reduction strategy or rewriting strategy is a relation specifying a rewrite for each object or term, compatible with a given reduction relation. Some authors use the term to refer to an evaluation strategy.

Patrick Denis Lincoln is an American computer scientist leading the Computer Science Laboratory (CSL) at SRI International. Educated at MIT and then Stanford, he joined SRI in 1989 and became director of the CSL around 1998. He previously held positions with ETA Systems, Los Alamos National Laboratory, and MCC.

In mathematical logic, System U and System U are pure type systems, i.e. special forms of a typed lambda calculus with an arbitrary number of sorts, axioms and rules. They were both proved inconsistent by Jean-Yves Girard in 1972. This result led to the realization that Martin-Löf's original 1971 type theory was inconsistent as it allowed the same "Type in Type" behaviour that Girard's paradox exploits.

José Meseguer is a Spanish computer scientist, and professor at the University of Illinois at Urbana–Champaign. He leads the university's Formal Methods and Declarative Languages Laboratory.

References

  1. "The Maude System:About". The Maude System. Retrieved 27 August 2021.
  2. "The Maude Project and Team". The Maude System. Retrieved 27 August 2021.

Further reading