Giovanni Conforti

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.

Spatial logics for bigraphs

Bigraphs are emerging as an interesting model for concurrent calculi, like CCS, pi-calculus, and Petri nets. Bigraphs are built orthogonally on two structures: a hierarchical place graph for locations and a link (hyper-)graph for connections. With the aim of describing bigraphical structures, we introduce a general framework for logics whose terms represent arrows in monoidal categories. We then instantiate the framework to bigraphical structures and obtain a logic that is a natural composition of a place graph logic and a link graph logic. We explore the concepts of separation and sharing in these logics and we prove that they generalise some known spatial logics for trees, graphs and tree contexts.

Decidability of Freshness, Undecidability of Revelation

We study decidability of a logic for describing processes with restricted names. We choose a minimal fragment of the Ambient Logic, but the techniques we present should apply to every logic which uses Cardelli and Gordon revelation and hiding operators, and Gabbay and Pitts freshness quantifier. We start from the static fragment of ambient logic that Calcagno, Cardelli and Gordon proved to be decidable. We prove that the addition of a hiding quantifier makes the logic undecidable. Hiding can be decomposed as freshness plus revelation. Quite surprisingly, freshness alone is decidable, but revelation alone is not.

TQL Algebra and its Implementation

TQL is a query language for semi-structured data. TQL binding mechanism is based upon the ambient logic. This binding mechanism is the key feature of TQL, but its implementation is far from obvious, being based on a logic which includes “difficult” operators such as negation, universal quantification, recursion, and new tree-related operators. In [6] an “implementation model” is presented, here we first extend it with tree operations, hence obtaining an algebra for the full TQL language. Then we shortly describe the evaluation techniques that we exploit in the actual implementation.

Scalable Query Dissemination in XPeer

This paper presents XPeer, a data sharing system for massively distributed XML data. XPeer allows users to publish and query heterogeneous information without any significant administration efforts. XPeer tries to dispatch any given query to all and only the potentially relevant peers, exploiting a superpeer network to this aim.