Giorgio Ghelli

Mobility Types for Mobile Ambients

An ambient is a named cluster of processes and subambients, which moves as a group.We describe type systems able to guarantee that certain ambients will remain immobile, and that certain ambients will not be dissolved by their environment.

A Spatial Logic for Querying Graphs

We study a spatial logic for reasoning about labelled directed graphs, and the application of this logic to provide a query language for analysing and manipulating such graphs. We give a graph description using constructs from process algebra. We introduce a spatial logic in order to reason locally about disjoint subgraphs. We extend our logic to provide a query language which preserves the multiset semantics of our graph model. Our approach contrasts with the more traditional set-based semantics found in query languages such as TQL, Strudel and GraphLog.

Ambient Groups and Mobility Types

We add name groups and group creation to the typed ambient calculus. Group creation is surprisingly interesting: it has the effect of statically preventing certain communications, and can thus block the accidental or malicious escape of capabilities that is a major concern in practical systems. Moreover, ambient groups allow us to refine our earlier work on type systems for ambient mobility. We present type systems in which groups identify the set of ambients that a process may cross or open.

A Query Language Based on the Ambient Logic

The ambient logic is a modal logic proposed to describe the structural and computational properties of distributed and mobile computation. The structural part of the ambient logic is, essentially, a logic of labeled trees, hence it turns out to be a good foundation for query languages for semistructured data, much in the same way as first order logic is a fitting foundation for relational query languages. We define here a query language for semistructured data that is based on the ambient logic, and we outline an execution model for this language. The language turns out to be quite expressive. Its strong foundations and the equivalences that hold in the ambient logic are helpful in the definition of the language semantics and execution model.

Secrecy and Group Creation

We add an operation of group creation to the typed π-calculus, where a group is a type for channels. Creation of fresh groups has the effect of statically preventing certain communications, and can block the accidental or malicious leakage of secrets. Intuitively, no channel belonging to a fresh group can be received by processes outside the initial scope of the group, even if those processes are untyped. We formalize this intuition by adapting a notion of secrecy introduced by Abadi, and proving a preservation of secrecy property.

Types for the ambient calculus

The ambient calculus is a concurrent calculus where the unifying notion of ambient is used to model many different constructs for distributed and mobile computation. We study a type system that describes several properties of ambient behavior. The type system allows ambients to be partitioned in disjoint sets (groups), according to the intended design of a system, in order to specify both the communication and the mobility behavior of ambients.

A calculus for overloaded functions with subtyping

We present a simple extension of typed λ-claculus where functions can be overloaded by adding different “pieces of code”. In short, the code of an overloaded function is formed by several branches of code; the branch to execute is chosen, when the function is applied, according to a particular selection rule which depends on the type of the argument. The crucial feature of the present approach is that a subtyping relation is defied among types, such that the type of a term generally decreases during computation, and this fact induces a distinction between the “compile-time” type and the “run-time”type of a term. We study the case of overloaded functions where the branch selection depends on the run-time type of the argument, so that overloading cannot be eliminated by a static analysis of code, but is an essential feature to be dealt with during computation. We prove Confluence and Strong Normalization for this calculus as well as a generalized Subject-Reduction theorem (but proofs are ommitted in this abstract. The definition of this calculus is driven by the understanding of object-oriented features and the connections between our calculus and object-orientedness are extensively stressed. We show that this calculus provides a foundation for typed object-oriented languages which solves some of the problems of the standard record-based approach. It also provides a type-discipline for a relevant fragment of the “core framework” of CLOS.

Fibonacci: a programming language for object databases

Fibonacci is an object-oriented database programming language characterized by static and strong typing, and by new mechanisms for modeling data-bases in terms of objects with roles, classes, and associations. A brief introduction to the language is provided to present those features, which are particularly suited to modeling complex databases. Examples of the use of Fibonacci are given with reference to the prototype implementation of the language.

TQL: a query language for semistructured data based on the ambient logic

The ambient logic is a modal logic that was proposed for the description of the structural and computational properties of distributed and mobile computation. The structural part of the ambient logic is, essentially, a logic of labelled trees, hence it turns out to be a good foundation for query languages for semistructured data, much in the same way as first-order logic is a fitting foundation for relational query languages. We define here a query language for semistructured data that is based on the ambient logic, and we outline an execution model for this language. The language turns out to be quite expressive. Its strong foundations and the equivalences that hold in the ambient logic are helpful in the definition of the language semantics and execution model.

XPeer: a self-organizing XML P2P database system

This paper describes XPeer , a zero-administration system for sharing and querying XML data The system allows users to share XML data without significant human intervention, and to pose XQuery FLWR queries against them The proposed system can be used in any application field, being a general purpose XML p2p DBMS, even though its main application is the management of resource descriptions in GRID environments.