The Larch Family of Specification Languages

Abstract

Larch specifications are T he use of suitable formalisms in extensive checking of specificatwo-tiered. Each one I the specification of computer tions as they are being conprograms and parts of computer prostructed. An important aspect of has a component grams offers significant advantages.' our approach is the use of a written in an algebraic Although there is considerable theo-powerful theorem prover for language and another retical interest in this area,2 practical semantic checking to supplement tailored toa experience is rather limited. The Larch the syntactic checking commonly tailored to a Project, a research project intended to defined for specification lanprogramming language. have practical applications in the next guages. few years, is developing tools and * Localizedprogramming language techniques to aid in the productive dependencies. Each Larch interapplication of formal specifications. A face language encapsulates the major part of the project is a family of features needed to write concise specification languages. Each specifiand comprehensible specifications cation has components written in two for a particular programming lanlanguages. The Larch interface language and incorporates Larch guages are particular to specific proShared Language specifications gramming languages, while the Larch in a uniform way. Shared Language is common to allThe Larch interface languages speclanguages.ify program modules, providing information needed to write programs Some important aspects of the that use these modules (Figure 1)' A Larch family of specification languages critical part of the interface is how the are module communicates with its envi-* Composability. The Larch lan-ronment, yet communication mechaguages are designed for the incre-nisms differ from programming lanmental construction of specifica-guage to programming language, tions from other specifications. sometimes in subtle ways. We have * Emphasis on presentation. The found it easier to be precise about Larch languages are designed to communication when the specification be readable. Among other things, language reflects the programming Larch's composition mechanisms language. Such specifications are genare defined as operations on spe-erally shorter than those written in a cifications, rather than on theories "universal" interface language. They or models.3 also seem clearer to programmers who * Suitability for integrated inter-implement modules and to programactive tools. The Larch languages mers who use them. are designed to facilitate the interEach Larch interface language deals active construction and incre-with what can be observed about the mental checking of specifications. behavior of programs written in a * Semantic checking. The Larch particular programming language. It languages are designed to enable provides a way to write assertions 24 0740-7459/85/0900/0024$O1.OO © 1985 IEEE IEEE SOFTWARE

Reusable software components

“…specification (Guttag et al, 1985;Wing, 1987) and model-based specification (Bjørner et al, 1987;Spivey, 1989). Both are based on the idea that abstract component behavior can be explained through mathematical modeling of program objects by mathematical objects.…”

“…Two modern specification languages of this kind support both the algebraic and the model-based style: Larch (Guttag et al, 1985;Liskov and Guttag, 1986;Wing, 1987) and Z (Spivey, 1989). Both permit the specifier to define mathematical theories and then to define abstract program interfaces using those theories.…”

“…In Larch, a mathematical theory is written in the Larch Shared Language (Guttag et al, 1985;Guttag and Horning, 1986a) and a program interface specification is written in an implementationlanguage-specific Larch Interface Language (Wing, 1987). Larch can be used to write specifications in either the algebraic or the model-based style, but the main catalog of published examples (Guttag and Horning, 1986b) clearly favors the algebraic style.…”

Writing Larch interface language specifications

“…The set of tools includes language-sensitive editors and semantic checkers based on a powerful theorem prover [13,361. The Larch family of specification languages [22] includes the design and formal definitions of the Larch Shared Language [24] and Larch interface languages [51]. These languages were designed to support the specification technique called "the two-tiered approach," which was first introduced in [19] and elaborated upon in the author's Ph.D. thesis [51].…”

A brief summary of VSPEC

“…To address such problems, vspec [2,3,4,5] augments vhdl to provide a declarative requirements specification capability that support rigorous, formal analysis. vspec is a Larch interface language [6,7] for vhdl. The Larch family of specification languages supports a two-tiered, model-based approach to specifying software.…”