Roberto Di Cosmo

Package upgrades in FOSS distributions: details and challenges

The upgrade problems faced by Free and Open Source Software distributions have characteristics not easily found elsewhere. We describe the structure of packages and their role in the upgrade process. We show that state of the art package managers have shortcomings inhibiting their ability to cope with frequent upgrade failures. We survey current counter-measures to such failures, argue that they are not satisfactory, and sketch alternative solutions.

Supporting software evolution in component-based FOSS systems

FOSS (Free and Open Source Software) systems present interesting challenges in system evolution. On one hand, most FOSS systems are based on very fine-grained units of software deployment-called packages-which promote system evolution; on the other hand, FOSS systems are among the largest software systems known and require sophisticated static and dynamic conditions to be verified, in order to successfully deploy upgrades on users machines. The slightest error in one of these conditions can turn a routine upgrade into a system administrators nightmare. In this paper we introduce a model-based approach to support the upgrade of FOSS systems. The approach promotes the simulation of upgrades to predict failures before affecting the real system. Both fine-grained static aspects (e.g. configuration incoherences) and dynamic aspects (e.g. the execution of configuration scripts) are taken into account, improving over the state of the art of upgrade planners. The effectiveness of the approach is validated by instantiating the approach to widely-used FOSS distributions.

Feature diagrams as package dependencies

FOSS (Free and Open Source Software) distributions use dependencies and package managers to maintain huge collections of packages and their installations; recent research have led to efficient and complete configuration tools and techniques, based on state of the art solvers, that are being adopted in industry. We show how to encode a significant subset of Free Feature Diagrams as interdependent packages, enabling to reuse package tools and research results into software product lines.

Predicting upgrade failures using dependency analysis

Upgrades in component based systems can disrupt other components. Being able to predict the possible consequence of an upgrade just by analysing inter-component dependencies can avoid errors and downtime. In this paper we precisely identify in a repository the components p whose upgrades force a large set of others components to be upgraded. We are also able to discriminate whether all the future versions of p have the same impact, or whether there are different classes of future versions that have different impacts. We perform our analysis on Debian, one of the largest FOSS distributions.

On isomorphisms of intersection types

The study of type isomorphisms for different λ-calculi started over twenty years ago, and a very wide body of knowledge has been established, both in terms of results and in terms of techniques. A notable missing piece of the puzzle was the characterization of type isomorphisms in the presence of intersection types. While, at first thought, this may seem to be a simple exercise, it turns out that not only finding the right characterization is not simple, but that the very notion of isomorphism in intersection types is an unexpectedly original element in the previously known landscape, breaking most of the known properties of isomorphisms of the typed λ-calculus. In particular, isomorphism is not a congruence and types that are equal in the standard models of intersection types may be nonisomorphic.

Learning from the future of component repositories

An important aspect of the quality assurance of large component repositories is to ensure the logical coherence of component metadata, and to this end one needs to identify incoherences as early as possible. Some relevant classes of problems can be formulated in term of properties of the future repositories into which the current repository may evolve. However, checking such properties on all possible future repositories requires a way to construct a finite representation of the infinite set of all potential futures. A class of properties for which this can be done is presented in this work. n nWe illustrate the practical usefulness of the approach with two quality assurance applications: (i) establishing the amount of “forced upgrades” induced by introducing new versions of existing components in a repository, and (ii) identifying outdated components that are currently not installable and need to be upgraded in order to become installable again. For both applications we provide experience reports obtained on the Debian free software distribution.

On Isomorphisms of Intersection Types

The study of type isomorphisms for different i¾?-calculi started over twenty years ago, and a very wide body of knowledge has been established, both in terms of results and in terms of techniques. A notable missing piece of the puzzle was the characterization of type isomorphisms in the presence of intersection types. While at first thought this may seem to be a simple exercise, it turns out that not only finding the right characterization is not simple, but that the very notion of isomorphism in intersection types is an unexpectedly original element in the previously known landscape, breaking most of the known properties of isomorphisms of the typed i¾?-calculus. In particular, types that are equal in the standard models of intersection types may be non-isomorphic.

Identifiers for Digital Objects: the Case of Software Source Code Preservation

Type theories with equality reflection, such as extensional type theory (ETT), are convenient theories in which to formalise mathematics, as they make it possible to consider provably equal terms as convertible. Although type-checking is undecidable in this context, variants of ETT have been implemented, for example in NuPRL and more recently in Andromeda. The actual objects that can be checked are not proof-terms, but derivations of proof-terms. This suggests that any derivation of ETT can be translated into a typecheckable proof term of intensional type theory (ITT). However, this result, investigated categorically by Hofmann in 1995, and 10 years later more syntactically by Oury, has never given rise to an effective translation. In this paper, we provide the first syntactical translation from ETT to ITT with uniqueness of identity proofs and functional extensionality. This translation has been defined and proven correct in Coq and yields an executable plugin that translates a derivation in ETT into an actual Coq typing judgment. Additionally, we show how this result is extended in the context of homotopy to a two-level type theory.We propose a generic approach to make arithmetic decision procedures designed for the concrete data-type Z of Coq available for alternative representations of integers. It is based on a transfer tool recently developped by Zimmermann and Herbelin to perform automatic and transparent transfer of theorems along isomorphisms.