Joseph A. Goguen

Security Policies and Security Models

We assune that the reader is familiar with the ubiquity of information in the modern world and is sympathetic with the need for restricting rights to read, add, modify, or delete information in specific contexts. This need is particularly acute for systems having computers as significant components.

Institutions: abstract model theory for specification and programming

There is a population explosion among the logical systems used in computing science. Examples include first-order logic, equational logic, Horn-clause logic, higher-order logic, infinitary logic, dynamic logic, intuitionistic logic, order-sorted logic, and temporal logic; moreover, there is a tendency for each theorem prover to have its own idiosyncratic logical system. The concept of institution is introduced to formalize the informal notion of “logical system.” The major requirement is that there is a satisfaction relation between models and sentences that is consistent under change of notation. Institutions enable abstracting away from syntactic and semantic detail when working on language structure “in-the-large”; for example, we can define language features for building large logical system. This applies to both specification languages and programming languages. Institutions also have applications to such areas as database theory and the semantics of artificial and natural languages. A first main result of this paper says that any institution such that signatures (which define notation) can be glued together, also allows gluing together theories (which are just collections of sentences over a fixed signature). A second main result considers when theory structuring is preserved by institution morphisms. A third main result gives conditions under which it is sound to use a theorem prover for one institution on theories from another. A fourth main result shows how to extend institutions so that their theories may include, in addition to the original sentences, various kinds of constraint that are useful for defining abstract data types, including both “data” and “hierarchy” constraints. Further results show how to define institutions that allow sentences and constraints from two or more institutions. All our general results apply to such “duplex” and “multiplex” institutions.

Initial Algebra Semantics and Continuous Algebras

Many apparently divergent approaches to specifying formal semantics of programming languages are applications of initial algebra semantics. In this paper an overview of initial algebra semantics is provided. The major technical feature is an initial continuous algebra which permits unified algebraic treatment of iterative and recursive semantic features in the same framework as more basic operations.

Principles of OBJ2

0~12 is a functional programming language with an underlying formal semantics that is based upon equational logic, and an oprtationnl semantics that is based upon rewrite rules. Four clsssrs of design principles for 01352 ate discussed briefly in this inttoduct,ion, and then in mote detail brlnw: (1) motlulntizntion and patnmcteriantion; (2) subsorts; (3) implcmcntnt.ion IcBchniquc>s; and (4) inlrtaction and flexibility. WC also lrace C)II.l history, current shtus, and future plans, and give n fairly comp1rl.c OnJ bibliography. blast rxnmplc codr hns n-ct,unlly bcbcn run on out currclnt OI%.JZ intcrprc,t (‘r.

The Semantics of CLEAR, A Specification Language

This paper gives a semantics for the Clear language for specifying problems and programs, described by Burstall and Goguen in 1977. A blend of denotational semantics with categorical ideas is used.

Techniques for requirements elicitation

The authors survey and evaluate techniques for eliciting requirements of computer-based systems, paying particular attention to dealing with social issues. The methods surveyed include introspection, interviews, questionnaires, and protocol, conversation, interaction, and discourse analyses. The last three techniques grew out of ethnomethodology and sociolinguistics. They can elicit tacit knowledge by observing actual interactions in the workplace, and can also be applied to the system development process itself.<<ETX>>

Order-sorted algebra I: equational deduction for multiple inheritance, overloading, exceptions and partial operations

Abstract This paper generalizes many-sorted algebra (MSA) to order-sorted algebra (OSA) by allowing a partial ordering relation on the set of sorts. This supports abstract data types with multiple inheritance (in roughly the sense of object-oriented programming), several forms of polymorphism and overloading, partial operations (as total on equationally defined subsorts), exception handling, and an operational semantics based on term rewriting. We give the basic algebraic constructions for OSA, including quotient, image, product and term algebra, and we prove their basic properties, including quotient, homomorphism, and initiality theorems. The papers major mathematical results include a notion of OSA deduction, a completeness theorem for it, and an OSA Birkhoff variety theorem. We also develop conditional OSA, including initiality, completeness, and McKinsey-Malcev quasivariety theorems, and we reduce OSA to (conditional) MSA, which allows lifting many known MSA results to OSA. Retracts, which intuitively are left inverses to subsort inclusions, provide relatively inexpensive run-time error handling. We show that it is safe to add retracts to any OSA signature, in the sense that it gives rise to a conservative extension. A final section compares and contrasts many different approaches to OSA. This paper also includes several examples demonstrating the flexibility and applicability of OSA, including some standard benchmarks like stack and list , as well as a much more substantial example, the number hierarchy from the naturals up to the quaternions.

Unwinding and Inference Control

This paper discusses two main ideas, unwinding and inference control. While both concern computer security, they are not closely related to each other. Unwinding is a verification technique for general security requirements based on noninterference assertions as in [Goguen & Meseguer 82a]. The inference control problem concerns preventing inference of unauthorized information by combining authorized information. The main result in this paper is an unwinding theorem that gives a very simple necessary and sufficient condition for a system to satisfy the MLS security policy system. A subsidiary topic is secure interfaces, which we show how to treat with noninterferce assertions.

A hidden agenda

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A categorical manifesto

This paper tries to explain why and how category theory is useful in computing science, by giving guidelines for applying seven basic categorical concepts: category, functor, natural transformation, limit, adjoint, colimit and comma category. Some examples, intuition, and references are given for each concept, but completeness is not attempted. Some additional categorical concepts and some suggestions for further research are also mentioned. The paper concludes with some philosophical discussion.