In reverse engineering of database queries, we aim to construct a query from a given set of answers and non-answers; it can then be used to explore the data further or as an explanation of the answers and non-answers. We investigate this query-by-example problem for queries formulated in positive fragments of linear temporal logic LTL over timestamped data, focusing on the design of suitable query languages and the combined and data complexity of deciding whether there exists a query in the given language that separates the given answers from non-answers. We consider both plain LTL queries and those mediated by LTL ontologies.

Copyright © 2019 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved This paper presents and compares three mechanisms for learning an ontology describing a domain of discoursed as defined in a collection of tweets. The task in part involves the identification of entities and relations in the free text data, which can then be used to produce a set of RDF triples from which an ontology can be generated. The first mechanism is therefore founded on the Stanford CoreNLP Toolkit.; in particular the Named Entity Recognition and Relation Extraction mechanisms that come with this tool kit. The second is founded on the GATE General Architecture for Text Engineering which provides an alternative mechanism for relation extraction from text. Both require a substantial amount of training data. To reduce the training data requirement the third mechanism is founded on the concept of Regular Expressions extracted from a training data “seed set”. Although the third mechanism still requires training data the amount of training data is significantly reduced without adversely affecting the quality of the ontologies generated.

In this paper, we present a SDDB scheme regarding document-based store that satisfies three security requirements: confidentiality, flexible access control, and querying over encrypted data. The scheme is inspired by PIRATTE and CryptDB concepts. PIRATTE is a proxy for sharing encrypted files through a social network between the data owner and the number of users and the files are decrypted on user side with the proxy key, whereas in CryptDB, it is proxy between a database and one user to encrypt or decrypt data based on user’s queries. The scheme also improves CryptDB security and provides the possibility of sharing data with multi-users through PIRATTE concept which is used to verify authentication on the proxy side.

We investigate the problem of learning description logic (DL) ontologies in Angluin et al.’s framework of exact learning via queries posed to an oracle. We consider membership queries of the form “is a tuple a of individuals a certain answer to a data retrieval query q in a given ABox and the unknown target ontology?” and completeness queries of the form “does a hypothesis ontology entail the unknown target ontology?” Given a DL L and a data retrieval query language Q, we study polynomial learnability of ontologies in L using data retrieval queries in Q and provide an almost complete classification for DLs that are fragments of EL with role inclusions and of DL-Lite and for data retrieval queries that range from atomic queries and EL/ELI-instance queries to conjunctive queries. Some results are proved by non-trivial reductions to learning from subsumption examples.

This paper describes work on a distributed framework for collaborative multi-robot localisation and mapping with large teams of Micro Aerial Vehicles (MAVs). We demonstrate the benefits of running both image capture and frame-to-frame tracking on the same device while offloading the more computationally intensive aspects of map creation and optimization to an off-board computer. We show no impact on the accuracy of pose estimates of this distributed approach and indeed demonstrate a robustness to delay that improves localisation performance. The bandwidth requirements of our system are much lower than similar systems which enables us to accommodate larger teams of MAVs. In the results section we demonstrate the performance of our system in both simulated and real-world environments.

It is known that no algorithm can extract the minimal depleting Σ-module from ontologies in expressive description logics (DLs). Thus research has focused on algorithms that approximate minimal depleting modules ‘from above’ by computing a depleting module that is not necessarily minimal. The first contribution of this paper is an implementation (AMEX) of such a depleting module extraction algorithm for expressive acyclic DL ontologies that uses a QBF solver for checking conservative extensions relativised to singleton interpretations. To evaluate AMEX and other module extraction algorithms we propose an algorithm approximating minimal depleting modules ‘from below’ (which also uses a QBF solver). We present experiments based on NCI (the National Cancer Institute Thesaurus) that indicate that our lower approximation often coincides with (or is very close to) the upper approximation computed by AMEX, thus proving for the first time that an approximation algorithm for minimal depleting modules can be almost optimal on a large ontology. We use the same technique to evaluate locality-based module extraction and a hybrid approach on NCI.

In this paper we consider the deductive verification of propositional temporal logic specifications of symmetric systems. In particular, we provide a heuristic approach to the scalability problems associated with analysing properties of large numbers of processes. Essentially, we use a temporal resolution procedure to verify properties of a system with few processes and then generalise the outcome in order to reduce the verification complexity of the same system with much larger numbers of processes. This provides a practical route to deductive verification for many systems comprising identical processes.

We study a logic-based approach to versioning of ontologies. Under this view, ontologies provide answers to queries about some vocabulary of interest. The difference between two versions of an ontology is given by the set of queries that receive different answers. We investigate this approach for terminologies given in the description logic EL extended with role inclusions and domain and range restrictions for three distinct types of queries: subsumption, instance, and conjunctive queries. In all three cases, we present polynomial-time algorithms that decide whether two terminologies give the same answers to queries over a given vocabulary and compute a succinct representation of the difference if it is non- empty. We present an implementation, CEX2, of the developed algorithms for subsumption and instance queries and apply it to distinct versions of Snomed CT and the NCI ontology.

The OWL 2 profile OWL 2 QL, based on the DL-Lite family of description logics, is emerging as a major language for developing new ontologies and approximating the existing ones. Its main application is ontology-based data access, where ontologies are used to provide background knowledge for answering queries over data. We investigate the corresponding notion of query inseparability (or equivalence) for OWL 2 QL ontologies and show that deciding query inseparability is PSPACE-hard and in EXPTIME. We give polynomial time (incomplete) algorithms and demonstrate by experiments that they can be used for practical module extraction.

The aim of this paper is to study semantic notions of modularity in description logic (DL) terminologies and reasoning problems that are relevant for modularity. We define two notions of a module whose independence is formalised in a model-theoretic way. Focusing mainly on the DLs ℰℒ and 𝒜ℒ𝒞, we then develop algorithms for module extraction, for checking whether a part of a terminology is a module, and for a number of related problems. We also analyse the complexity of these problems, which ranges from tractable to undecidable. Finally, we provide an experimental evaluation of our module extraction algorithms based on the large-scale terminology SNOMED CT.

In this paper we consider the specification and verification of infinite-state systems using temporal logic. In particular, we describe parameterised systems using a new variety of first-order temporal logic that is both powerful enough for this form of specification and tractable enough for practical deductive verification. Importantly, the power of the temporal language allows us to describe (and verify) asynchronous systems, communication delays and more complex liveness and fairness properties. These aspects appear difficult for many other approaches to infinite-state verification.

In this paper, we consider a tractable sub-class of propositional linear time temporal logic, and provide a complete clausal resolution calculus for it. The fragment is important as it can be used to represent simple Buchi automata. We also show that, just as the emptiness check for a Buchi automaton is tractable, the complexity of deciding unsatisfiability, via resolution, of our logic is polynomial (rather than exponential). Consequently, a Buchi automaton can be represented within our logic, and its emptiness can be tractably decided via deductive methods. This may have a significant impact upon approaches to verification, since techniques such as model checking inherently depend on the ability to check emptiness of an appropriate Buchi automaton. Thus, we also discuss how such a logic might form the basis for practical deductive temporal verification

Until recently, First-Order Temporal Logic (FOTL) has been only partially understood. While it is well known that the full logic has no finite axiomatisation, a more detailed analysis of fragments of the logic was not previously available. However, a breakthrough by Hodkinson et al., identifying a finitely axiomatisable fragment, termed the monodic fragment, has led to improved understanding of FOTL. Yet, in order to utilise these theoretical advances, it is important to have appropriate proof techniques for this monodic fragment.In this paper, we modify and extend the clausal temporal resolution technique, originally developed for propositional temporal logics, to enable its use in such monodic fragments. We develop a specific normal form for monodic formulae in FOTL, and provide a complete resolution calculus for formulae in this form. Not only is this clausal resolution technique useful as a practical proof technique for certain monodic classes, but the use of this approach provides us with increased understanding of the monodic fragment. In particular, we here show how several features of monodic FOTL can be established as corollaries of the completeness result for the clausal temporal resolution method. These include definitions of new decidable monodic classes, simplification of existing monodic classes by reductions, and completeness of clausal temporal resolution in the case of monodic logics with expanding domains, a case with much significance in both theory and practice.

First-order temporal logic is a concise and powerful notation, with many potential applications in both Computer Science and Artificial Intelligence. While the full logic is highly complex, recent work on monodic first-order temporal logics has identified important enumerable and even decidable fragments. In this paper, we develop a clausal resolution method for the monodic fragment of first-order temporal logic over expanding domains. We first define a normal form for monodic formulae and then introduce novel resolution calculi that can be applied to formulae in this normal form. We state correctness and completeness results for the method. We illustrate the method on a comprehensive example. The method is based on classical first-order resolution and can, thus, be efficiently implemented.