Šiuo metu yra plačiai naudojamos ontologijos įvairiems uždaviniams spręsti. Dažnai susiduriama su problema kuriant naujas ontologijas, tai užima daug laiko. Darbo tikslas sukurti metodika, kuri nusakytų principus ontologijų jungimui bei moduliniam kūrimui. Analizuojant mokslinę literatūrą buvo nustatyti esami ontologijų jungimo bei kūrimo procesai. Tačiau, šie procesai neužtikrina korektiško ontologijų jungimo bei kūrimo. Todėl buvo detalizuoti konkretesni procesai, kuriais buvo parengta metodika. Siekiant praktiškai pritaikyti ir palyginti metodiką su kitomis analizės metu nagrinėtomis metodikomis, buvo sukurtas prototipas, kurio veikimas grįstas parengta metodika. Eksperimento metu buvo jungiamos bei kuriamos naujos ontologijos. Įvertinus gautus rezultatus buvo pastebėta jog, parengta ontologijų modulinio kūrimo ir jungimo metodika leidžia patogiau kurti bei jungti ontologijas naudojanti kitas ontologijas ar jų dalis. / At present, ontologies are widely used for various tasks. The main problem is that takes a lot of time of creating new ontologies. There are no methodologies which allow to merge ontologies or reuse various parts of ontology. The aim of research is to create the methodology of modular development and linking OWL 2 ontologies. This work covers analysis how to create and link the ontologies. During the research, a process was specified for creating and linking ontologies. This process allows creating modular ontologies for better maintenance and reuse. The experiment was accomplished in order to compare the new methodology whit existing one by creating a prototypical tool for merging ontologies. Three ontologies were created and merged using the prototype tool and Protégé. A comparison of results has shown the advantages of the created prototypical tool and methodology behind it against existing ones. The new methodology allows easily merging ontologies and creating new ontologies by reusing various parts of existing ontologies.

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We present an FCA-based axiomatization method that produces a complete EL TBox (the terminological part of an OWL 2 EL ontology) from a graph dataset in at most exponential time. We describe technical details that allow for efficient implementation as well as variations that dispense with the computation of extremely large axioms, thereby rendering the approach applicable albeit some completeness is lost. Moreover, we evaluate the prototype on real-world datasets. / This is an extended version of an article accepted at AAAI 2024.

Description logics (DLs) are knowledge representation formalisms with numerous applications and well-understood model-theoretic semantics and computational properties. SRIQ is a DL that provides the logical underpinning for the semantic web language OWL 2, which is the W3C standard for knowledge representation on the web. A central component of most DL applications is an efficient and scalable reasoner, which provides services such as consistency testing and classification. Despite major advances in DL reasoning algorithms over the last decade, however, ontologies are still encountered in practice that cannot be handled by existing DL reasoners. Consequence-based calculi are a family of reasoning techniques for DLs. Such calculi have proved very effective in practice and enjoy a number of desirable theoretical properties. Up to now, however, they were proposed for either Horn DLs (which do not support disjunctive reasoning), or for DLs without cardinality constraints. In this thesis we present a novel consequence-based algorithm for TBox reasoning in SRIQ - a DL that supports both disjunctions and cardinality constraints. Combining the two features is non-trivial since the intermediate consequences that need to be derived during reasoning cannot be captured using DLs themselves. Furthermore, cardinality constraints require reasoning over equality, which we handle using the framework of ordered paramodulation - a state-of-the-art method for equational theorem proving. We thus obtain a calculus that can handle an expressive DL, while still enjoying all the favourable properties of existing consequence-based algorithms, namely optimal worst-case complexity, one-pass classification, and pay-as-you-go behaviour. To evaluate the practicability of our calculus, we implemented it in Sequoia - a new DL reasoning system. Empirical results show substantial robustness improvements over well-established algorithms and implementations, and performance competitive with closely related work.

OWL 2 EL is a popular ontology language that is based on the EL family of description logics and supports regular role inclusions,axioms that can capture compositional properties of roles such as role transitivity and reflexivity. In this thesis, we present several novel complexity results and algorithms for answering expressive queries over OWL 2 EL knowledge bases (KBs) with regular role inclusions. We first focus on the complexity of conjunctive query (CQ) answering in OWL 2 EL and show that the problem is PSpace-complete in combined complexity, the complexity measured in the total size of the input. All the previously known approaches encode the regular role inclusions using finite automata that can be worst-case exponential in size, and thus are not optimal. In our PSpace procedure, we address this problem by using a novel, succinct encoding of regular role inclusions based on pushdown automata with a bounded stack. Moreover, we strengthen the known PSpace lower complexity bound and show that the problem is PSpace-hard even if we consider only the regular role inclusions as part of the input and the query is acyclic; thus, our algorithm is optimal in knowledge base complexity, the complexity measured in the size of the KB, as well as for acyclic queries. We then study graph queries for OWL 2 EL and show that answering positive, converse- free conjunctive graph queries is PSpace-complete. Thus, from a theoretical perspective, we can add navigational features to CQs over OWL 2 EL without an increase in complexity. Finally, we present a practicable algorithm for answering CQs over OWL 2 EL KBs with only transitive and reflexive composite roles. None of the previously known approaches target transitive and reflexive roles specifically, and so they all run in PSpace and do not provide a tight upper complexity bound. In contrast, our algorithm is optimal: it runs in NP in combined complexity and in PTime in KB complexity. We also show that answering CQs is NP-hard in combined complexity if the query is acyclic and the KB contains one transitive role, one reflexive role, or nominals—concepts containing precisely one individual.

This master's thesis describes importing the ontology in language OWL 2 into the internal structures of 4A annotation server. It is concerned in anonymous nodes, for example in anonymous classes or anonymous properties. The solution was to use the library The OWL API for import ontology. The solution also allows automatic generation of names to anonymous classes and properties.