Recent years witnessed a rising interest towards Datalog-based ontological
reasoning systems, both in academia and industry. These systems adopt
languages, often shared under the collective name of Datalog$+/-$, that extend
Datalog with the essential feature of existential quantification, while
introducing syntactic limitations to sustain reasoning decidability and achieve
a good trade-off between expressive power and computational complexity. From an
implementation perspective, modern reasoners borrow the vast experience of the
database community in developing streaming-based data processing systems, such
as volcano-iterator architectures, that sustain a limited memory footprint and
good scalability. In this paper, we focus on two extremely promising,
expressive, and tractable languages, namely, Shy and Warded Datalog$+/-$. We
leverage their theoretical underpinnings to introduce novel reasoning
techniques, technically, "chase variants", that are particularly fit for
efficient reasoning in streaming-based architectures. We then implement them in
Vadalog, our reference streaming-based engine, to efficiently solve ontological
reasoning tasks over real-world settings.

利用 Datalog+/- 语言中的 Shy 和 Warded Datalog+/- 以及引入的新型推理技术 'chase variants'，在基于流式处理架构中实现了 Vadalog 引擎，从而在真实环境中高效解决本体推理任务。

面向基于流式架构的约束型和保护型 Datalog$+-$ 的本体推理（技术报告）

Ontological Reasoning over Shy and Warded Datalog$+/-$ for  Streaming-based Architectures (technical report)

Existential rules are an expressive knowledge representation language mainly
developed to query data. In the literature, they are often supposed to be in
some normal form that simplifies technical developments. For instance, a common
assumption is that rule heads are atomic, i.e., restricted to a single atom.
Such assumptions are considered to be made without loss of generality as long
as all sets of rules can be normalised while preserving entailment. However, an
important question is whether the properties that ensure the decidability of
reasoning are preserved as well. We provide a systematic study of the impact of
these procedures on the different chase variants with respect to chase
(non-)termination and FO-rewritability. This also leads us to study open
problems related to chase termination of independent interest.

该研究系统研究了存在性规则对于不同的追踪变体以及基于一阶逻辑的重写的 (chase (non-) termination and FO-rewritability) 影响，从而探讨了相关的开放性问题。

存在规则的规范化：不是那么无害！

Normalisations of Existential Rules: Not so Innocuous!

Existential rules are a positive fragment of first-order logic that
generalizes function-free Horn rules by allowing existentially quantified
variables in rule heads. This family of languages has recently attracted
significant interest in the context of ontology-mediated query answering.
Forward chaining, also known as the chase, is a fundamental tool for computing
universal models of knowledge bases, which consist of existential rules and
facts. Several chase variants have been defined, which differ on the way they
handle redundancies. A set of existential rules is bounded if it ensures the
existence of a bound on the depth of the chase, independently from any set of
facts. Deciding if a set of rules is bounded is an undecidable problem for all
chase variants. Nevertheless, when computing universal models, knowing that a
set of rules is bounded for some chase variant does not help much in practice
if the bound remains unknown or even very large. Hence, we investigate the
decidability of the k-boundedness problem, which asks whether the depth of the
chase for a given set of rules is bounded by an integer k. We identify a
general property which, when satisfied by a chase variant, leads to the
decidability of k-boundedness. We then show that the main chase variants
satisfy this property, namely the oblivious, semi-oblivious (aka Skolem), and
restricted chase, as well as their breadth-first versions. This paper is under
consideration for publication in Theory and Practice of Logic Programming.

研究论文探讨了基于本体的查询应答中的万有模型问题，特别关注存在规则边界问题，提出了一般性质并证明了一些经典的 chase 变体满足该性质，进而解决了这些变体的有限深度问题。

追逐变种中的有界性特征

Characterizing Boundedness in Chase Variants

The chase is a fundamental tool for existential rules. Several chase variants
are known, which differ on how they handle redundancies possibly caused by the
introduction of nulls. Given a chase variant, the halting problem takes as
input a set of existential rules and asks if this set of rules ensures the
termination of the chase for any factbase. It is well-known that this problem
is undecidable for all known chase variants. The related problem of boundedness
asks if a given set of existential rules is bounded, i.e., whether there is a
predefined upper bound on the number of (breadth-first) steps of the chase,
independently from any factbase. This problem is already undecidable in the
specific case of datalog rules. However, knowing that a set of rules is bounded
for some chase variant does not help much in practice if the bound is unknown.
Hence, in this paper, we investigate the decidability of the k-boundedness
problem, which asks whether a given set of rules is bounded by an integer k. We
prove that k-boundedness is decidable for three chase variants, namely the
oblivious, semi-oblivious and restricted chase.

该论文研究对于三种追赶算法变种，如何确定给定规则集的有界性问题是可决的。