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A typebased approach to program security
 In Proceedings of the 7th International Joint Conference on the Theory and Practice of Software Development
, 1997
"... Abstract. This paper presents a type system which guarantees that welltyped programs in a procedural programming language satisfy a noninterference security property. With all program inputs and outputs classified at various security levels, the property basically states that a program output, clas ..."
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Abstract. This paper presents a type system which guarantees that welltyped programs in a procedural programming language satisfy a noninterference security property. With all program inputs and outputs classified at various security levels, the property basically states that a program output, classified at some level, can never change as a result of modifying only inputs classified at higher levels. Intuitively, this means the program does not “leak ” sensitive data. The property is similar to a notion introduced years ago by Goguen and Meseguer to model security in multilevel computer systems [7]. We also give an algorithm for inferring and simplifying principal types, which document the security requirements of programs. 1
Type inference with simple subtypes
 J. Funct. Program
, 1991
"... Subtyping appears in a variety of programming languages, in the form of the "automatic coercion " of integers to reals, Pascal subranges, and subtypes arising from class hierarchies in languages with inheritance. A general framework based on untyped lambda calculus provides a simple seman ..."
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Cited by 96 (2 self)
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Subtyping appears in a variety of programming languages, in the form of the "automatic coercion " of integers to reals, Pascal subranges, and subtypes arising from class hierarchies in languages with inheritance. A general framework based on untyped lambda calculus provides a simple semantic model of subtyping and is used to demonstrate that an extension of Curry’s type inference rules are semantically complete. An algorithm G for computing the most general typing associated with any giv en expression, and a restricted, optimized algorithm GA using only atomic subtyping hypotheses are developed. Both algorithms may be extended to insert type conversion functions at compile time or allow polymorphic function declarations as in ML. 1.
Principal Type Schemes for Functional Programs with Overloading and Subtyping
 Science of Computer Programming
, 1994
"... We show how the Hindley/Milner polymorphic type system can be extended to incorporate overloading and subtyping. Our approach is to attach constraints to quantified types in order to restrict the allowed instantiations of type variables. We present an algorithm for inferring principal types and ..."
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Cited by 47 (2 self)
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We show how the Hindley/Milner polymorphic type system can be extended to incorporate overloading and subtyping. Our approach is to attach constraints to quantified types in order to restrict the allowed instantiations of type variables. We present an algorithm for inferring principal types and prove its soundness and completeness. We find that it is necessary in practice to simplify the inferred types, and we describe techniques for type simplification that involve shape unification, strongly connected components, transitive reduction, and the monotonicities of type formulas.
Algorithmic Aspects of Type Inference With Subtypes
 In Conference Record of the Nineteenth Annual ACM Symposium on Principles of Programming Languages
, 1992
"... We study the complexity of type inference for programming languages with subtypes. There are three language variations that effect the problem: (i) basic functions may have polymorphic or more limited types, (ii) the subtype hierarchy may be fixed or vary as a result of subtype declarations within a ..."
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We study the complexity of type inference for programming languages with subtypes. There are three language variations that effect the problem: (i) basic functions may have polymorphic or more limited types, (ii) the subtype hierarchy may be fixed or vary as a result of subtype declarations within a program, and (iii) the subtype hierarchy may be an arbitrary partial order or may have a more restricted form, such as a tree or lattice. The naive algorithm for inferring a most general polymorphic type, under variable subtype hypotheses, requires deterministic exponential time. If we fix the subtype ordering, this upper bound grows to nondeterministic exponential time. We show that it is nphard to decide whether a lambda term has a type with respect to a fixed subtype hierarchy (involving only atomic type names). This lower bound applies to monomorphic or polymorphic languages. We give pspace upper bounds for deciding polymorphic typability if the subtype hierarchy has a lattice structur...
Satisfiability of Inequalities in a Poset
 Fundamenta Informaticae
"... We consider tractable and intractable cases of the satisfiability problem for conjunctions of inequalities between variables and constants in a fixed finite poset. We show that crowns are intractable. ..."
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We consider tractable and intractable cases of the satisfiability problem for conjunctions of inequalities between variables and constants in a fixed finite poset. We show that crowns are intractable.
Colouring, constraint satisfaction, and complexity
"... Constraint satisfaction problems have enjoyed much attention since the early seventies, and in the last decade have become also a focus of attention amongst theoreticians. Graph colourings are a special class of constraint satisfaction problems; they offer a microcosm of many of the considerations t ..."
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Cited by 18 (1 self)
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Constraint satisfaction problems have enjoyed much attention since the early seventies, and in the last decade have become also a focus of attention amongst theoreticians. Graph colourings are a special class of constraint satisfaction problems; they offer a microcosm of many of the considerations that occur in constraint satisfaction. From the point of view of theory, they are well known to exhibit a dichotomy of complexity the kcolouring problem is polynomial time solvable when k ≤ 2, and NPcomplete when k ≥ 3. Similar dichotomy has been proved for the class of graph homomorphism problems, which are intermediate problems between graph colouring and constraint satisfaction
Full Constraint Satisfaction Problems
"... Feder and Vardi have conjectured that all constraint satisfaction problems to a fixed structure(constraint language) are polynomial or NPcomplete. This socalled Dichotomy Conjecture remains open, although it has been proved in a number of special cases. Most recently, Bulatovhas verified the conje ..."
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Cited by 17 (8 self)
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Feder and Vardi have conjectured that all constraint satisfaction problems to a fixed structure(constraint language) are polynomial or NPcomplete. This socalled Dichotomy Conjecture remains open, although it has been proved in a number of special cases. Most recently, Bulatovhas verified the conjecture for conservative structures, i.e., structures which contain all possible unary relations.We explore three different implications of Bulatov's result. Firstly, the above dichotomy can be extended to socalled inclusive structures, corresponding to conservative constraintsatisfaction problems in which each variable comes with its own domain. (This has also been independently observed by Bulatov.) We prove a more general version, extending the dichotomyto socalled threeinclusive structures, i.e., structures which contain, with any unary relation R,all unary relations R0 for subsets R0 ` R with at most three elements.For the constraint satisfaction problems in this generalization we must restrict the instances to socalled 1full structures, in which each variable is involved in a unary constraint. This leadsto our second focus, which is on restrictions to more general kinds of `full ' input structures. For any set W of positive integers, we consider a restriction to Wfull input structures, i.e.,structures in which, for each w 2 W, any w variables are involved in a wary constraint. Weidentify a class of structures (the socalled Wsetfull structures) for which the restriction to Wfull input structures does not change the complexity of the constraint satisfaction problem,and hence the family of these restricted problems also exhibits dichotomy. The general family of threeinclusive constraint satisfaction problems restricted to Wfull input structures containsexamples which we cannot seem to prove either polynomial or NPcomplete. Nevertheless, we are able to use our result on the dichotomy for threeinclusive constraint satisfaction problems,to deduce the fact that all threeinclusive constraint satisfaction problems restricted to Wfullinput structures are NPcomplete or `quasipolynomial ' (of order nO(log n)).Our third focus deals with bounding the number of occurrences of a variable, which we
On the Integration of Functional Programming, ClassBased ObjectOriented Programming, and MultiMethods
, 1996
"... We present a new predicative and decidable type system, called ML , suitable for objectoriented languages with implicit polymorphism in the tradition of ML (cf. ..."
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Cited by 11 (2 self)
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We present a new predicative and decidable type system, called ML , suitable for objectoriented languages with implicit polymorphism in the tradition of ML (cf.
The CLP(OIH) Language
, 1998
"... Reproduction of all or part of this work is permitted for educational or research use on condition that this copyright notice is included in any copy. See back inner page for a list of recent BRICS Dissertation Series publications. Copies may be obtained by contacting: BRICS ..."
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Reproduction of all or part of this work is permitted for educational or research use on condition that this copyright notice is included in any copy. See back inner page for a list of recent BRICS Dissertation Series publications. Copies may be obtained by contacting: BRICS