444 research outputs found
Axiom Pinpointing
Axiom pinpointing refers to the task of finding the specific axioms in an
ontology which are responsible for a consequence to follow. This task has been
studied, under different names, in many research areas, leading to a
reformulation and reinvention of techniques. In this work, we present a general
overview to axiom pinpointing, providing the basic notions, different
approaches for solving it, and some variations and applications which have been
considered in the literature. This should serve as a starting point for
researchers interested in related problems, with an ample bibliography for
delving deeper into the details
Lassie: HOL4 Tactics by Example
Proof engineering efforts using interactive theorem proving have yielded
several impressive projects in software systems and mathematics. A key obstacle
to such efforts is the requirement that the domain expert is also an expert in
the low-level details in constructing the proof in a theorem prover. In
particular, the user needs to select a sequence of tactics that lead to a
successful proof, a task that in general requires knowledge of the exact names
and use of a large set of tactics.
We present Lassie, a tactic framework for the HOL4 theorem prover that allows
individual users to define their own tactic language by example and give
frequently used tactics or tactic combinations easier-to-remember names. The
core of Lassie is an extensible semantic parser, which allows the user to
interactively extend the tactic language through a process of definitional
generalization. Defining tactics in Lassie thus does not require any knowledge
in implementing custom tactics, while proofs written in Lassie retain the
correctness guarantees provided by the HOL4 system. We show through case
studies how Lassie can be used in small and larger proofs by novice and more
experienced interactive theorem prover users, and how we envision it to ease
the learning curve in a HOL4 tutorial
Semiring Provenance for Lightweight Description Logics
We investigate semiring provenance--a successful framework originally defined
in the relational database setting--for description logics. In this context,
the ontology axioms are annotated with elements of a commutative semiring and
these annotations are propagated to the ontology consequences in a way that
reflects how they are derived. We define a provenance semantics for a language
that encompasses several lightweight description logics and show its
relationships with semantics that have been defined for ontologies annotated
with a specific kind of annotation (such as fuzzy degrees). We show that under
some restrictions on the semiring, the semantics satisfies desirable properties
(such as extending the semiring provenance defined for databases). We then
focus on the well-known why-provenance, which allows to compute the semiring
provenance for every additively and multiplicatively idempotent commutative
semiring, and for which we study the complexity of problems related to the
provenance of an axiom or a conjunctive query answer. Finally, we consider two
more restricted cases which correspond to the so-called positive Boolean
provenance and lineage in the database setting. For these cases, we exhibit
relationships with well-known notions related to explanations in description
logics and complete our complexity analysis. As a side contribution, we provide
conditions on an ELHI_bot ontology that guarantee tractable reasoning.Comment: Paper currently under review. 102 page
Formal verification of higher-order probabilistic programs
Probabilistic programming provides a convenient lingua franca for writing
succinct and rigorous descriptions of probabilistic models and inference tasks.
Several probabilistic programming languages, including Anglican, Church or
Hakaru, derive their expressiveness from a powerful combination of continuous
distributions, conditioning, and higher-order functions. Although very
important for practical applications, these combined features raise fundamental
challenges for program semantics and verification. Several recent works offer
promising answers to these challenges, but their primary focus is on semantical
issues.
In this paper, we take a step further and we develop a set of program logics,
named PPV, for proving properties of programs written in an expressive
probabilistic higher-order language with continuous distributions and operators
for conditioning distributions by real-valued functions. Pleasingly, our
program logics retain the comfortable reasoning style of informal proofs thanks
to carefully selected axiomatizations of key results from probability theory.
The versatility of our logics is illustrated through the formal verification of
several intricate examples from statistics, probabilistic inference, and
machine learning. We further show the expressiveness of our logics by giving
sound embeddings of existing logics. In particular, we do this in a parametric
way by showing how the semantics idea of (unary and relational) TT-lifting can
be internalized in our logics. The soundness of PPV follows by interpreting
programs and assertions in quasi-Borel spaces (QBS), a recently proposed
variant of Borel spaces with a good structure for interpreting higher order
probabilistic programs
Semantic Relevance
International audienceAbstract A clause C is syntactically relevant in some clause set N , if it occurs in every refutation of N . A clause C is syntactically semi-relevant, if it occurs in some refutation of N . While syntactic relevance coincides with satisfiability (if C is syntactically relevant then N \ { C } is satisfiable), the semantic counterpart for syntactic semi-relevance was not known so far. Using the new notion of a conflict literal we show that for independent clause sets N a clause C is syntactically semi-relevant in the clause set N if and only if it adds to the number of conflict literals in N . A clause set is independent, if no clause out of the clause set is the consequence of different clauses from the clause set. Furthermore, we relate the notion of relevance to that of a minimally unsatisfiable subset (MUS) of some independent clause set N . In propositional logic, a clause C is relevant if it occurs in all MUSes of some clause set N and semi-relevant if it occurs in some MUS. For first-order logic the characterization needs to be refined with respect to ground instances of N and C
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