The CIFF Proof Procedure for Abductive Logic Programming with Constraints: Definition, Implementation and a Web Application

Abduction has found broad application as a powerful tool for hypothetical reasoning with incomplete knowledge, which can be handled by labeling some pieces of information as abducibles, i.e. as possible hypotheses that can be assumed to hold, provided that they are consistent with the given knowledge base. Attempts to make the abductive reasoning an effective computational tool gave rise to Abductive Logic Programming (ALP) which combines abduction with standard logic programming. A number of so-called proof procedures for ALP have been proposed in the literature, e.g. the IFF procedure, the Kakas and Mancarella procedure and the SLDNFA procedure, which rely upon extensions of different semantics for logic programming. ALP has also been integrated with Constraint Logic Programming (CLP), in order to combine abductive reasoning with an arithmetic tool for constraint solving. In recent years, many proof procedures for abductive logic programming with constraints have been proposed, including ACLP and the A-System which have been applied to many fields, e.g. multi-agent systems, scheduling, integration of information. This dissertation describes the development of a new abductive proof procedure with constraints, namely the CIFF proof procedure. The description is both at the theoretical level, giving a formal definition and a soundness result with respect to the three-valued completion semantics, and at the implementative level with the implemented CIFF System 4.0 as a Prolog meta-interpreter. The main contributions of the CIFF proof procedure are the advances in the expressiveness of the framework with respect to other frameworks for abductive logic programming with constraints, and the overall computational performances of the implemented system. The second part of the dissertation presents a novel application of the CIFF proof procedure as the computational engine of a tool, the CIFFWEB system, for checking and (possibly) repairing faulty web sites. Indeed, the exponential growth of the WWW raises the question of maintaining and automatically repairing web sites, in particular when the designers of these sites require them to exhibit certain properties at both structural and data level. The capability of maintaining and repairing web sites is also important to ensure the success of the Semantic Web vision. As the Semantic Web relies upon the definition and the maintenance of consistent data schemas (XML/XMLSchema, RDF/RDFSchema, OWL and so on), tools for reasoning over such schemas (and possibly extending the reasoning to multiple web pages) show great promise. The CIFFWEB system is such a tool which allows to verify and to repair XML web sites instances, against sets of requirements which have to be fulfilled, through abductive reasoning. We define an expressive characterization of rules for checking and repairing web sites' errors and we do a formal mapping of a fragment of a well known XML query language, namely Xcerpt, to abductive logic programs suitable to fed as input to the CIFF proof procedure. Finally, the CIFF proof procedure detects the errors and possibly suggests modifications to the XML instances to repair them. The soundness of this process is directly inherited from the soundness of CIFF

A theory of types for security and privacy

Im modernen Internet sind kryptographische Protokolle allgegenwärtig. Ihre Entwicklung ist jedoch schwierig und eine manuelle Sicherheitsanalyse mühsam und fehleranfällig. Ein Mangel an exakten Sicherheitsbeweisen führt daher zu oft gravierenden Sicherheitsmängeln in vielen Protokollen. Um Datenschutz und Sicherheit kryptographischer Protokolle zu verbessern und deren Verifikation zu vereinfachen, konzentriert sich ein Großteil der Forschung auf formale Protokollanalyse. Dies führte zur Entwicklung automatischer Tools, die auf symbolischen Kryptographie-Abstraktionen basieren. Jedoch gibt es weiterhin zahlreiche Protokolle und Sicherheitseigenschaften, deren Analyse zu komplex für aktuelle Systeme ist. Diese Dissertation stellt drei neuartige Frameworks zur Verifikation von Sicherheitsprotokollen und ihren Implementierungen vor. Sie nutzen eine leistungsstarker Typisierung für Sicherheit und Datenschutz und verbessern damit die aktuelle, Beschränkungen unterworfene Situation. Mit AF7 präsentieren wir die erste statische Typisierung von Protokollimplementierungen bezüglich Sicherheitseigenschaften, die in affiner Logik formuliert sind. Zudem sorgt unsere neuartige typbasierte, automatische Analysetechnik von elektronischen Wahlsystemen für Datenschutz und Überprüfbarkeit im Wahlprozess. Schließlich stellen wir mit DF7 das erste affine Typsystem zur statischen, automatischen Verifikation der sogenannten Distributed Differential Privacy in Protokollimplementierungen vor.Cryptographic protocols are ubiquitous in the modern web. However, they are notoriously difficult to design and their manual security analysis is both tedious and error-prone. Due to the lack of rigorous security proofs, many protocols have been discovered to be flawed. To improve the security and privacy guarantees of cryptographic protocols and their implementations and to facilitate their verification, a lot of research has been directed towards the formal analysis of such protocols. This has led to the development of several automated tools based on symbolic abstractions of cryptography. Unfortunately, there are still various cryptographic protocols and properties that are out of the scope of current systems. This thesis introduces three novel frameworks for the verification of security protocols and their implementations based on powerful types for security and privacy, overcoming the limitations of current state-of-the-art approaches. With AF7 we present the first type system that statically enforces the safety of cryptographic protocol implementations with respect to authorization policies expressed in affine logic. Furthermore, our novel approach for the automated analysis of e-voting systems based on refinement type systems can be used to enforce both privacy and verifiability. Finally, with DF7, we present the first affine, distanceaware type system to statically and automatically enforce distributed differential privacy in cryptographic protocol implementations

On the role of Computational Logic in Data Science: representing, learning, reasoning, and explaining knowledge

In this thesis we discuss in what ways computational logic (CL) and data science (DS) can jointly contribute to the management of knowledge within the scope of modern and future artificial intelligence (AI), and how technically-sound software technologies can be realised along the path. An agent-oriented mindset permeates the whole discussion, by stressing pivotal role of autonomous agents in exploiting both means to reach higher degrees of intelligence. Accordingly, the goals of this thesis are manifold. First, we elicit the analogies and differences among CL and DS, hence looking for possible synergies and complementarities along 4 major knowledge-related dimensions, namely representation, acquisition (a.k.a. learning), inference (a.k.a. reasoning), and explanation. In this regard, we propose a conceptual framework through which bridges these disciplines can be described and designed. We then survey the current state of the art of AI technologies, w.r.t. their capability to support bridging CL and DS in practice. After detecting lacks and opportunities, we propose the notion of logic ecosystem as the new conceptual, architectural, and technological solution supporting the incremental integration of symbolic and sub-symbolic AI. Finally, we discuss how our notion of logic ecosys- tem can be reified into actual software technology and extended towards many DS-related directions