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  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>November</journal-title>
      </journal-title-group>
      <issn pub-type="ppub">1613-0073</issn>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>Ontologies and Thesauri⋆</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Antonios Georgakopoulos</string-name>
          <email>a.georgakopoulos@uva.nl</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Jacco van Ossenbruggen</string-name>
          <email>jacco.van.ossenbruggen@vu.nl</email>
          <xref ref-type="aff" rid="aff1">1</xref>
          <xref ref-type="aff" rid="aff2">2</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Lise Stork</string-name>
          <email>l.stork@uva.nl</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Workshop</string-name>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Informatics Institute, University of Amsterdam</institution>
          ,
          <addr-line>1098 XH Amsterdam</addr-line>
          ,
          <country country="NL">The Netherlands</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Ontology, Thesaurus, Large Language Models, Knowledge Engineering</institution>
          ,
          <addr-line>Prompting, RAG, DRAGON-AI</addr-line>
        </aff>
        <aff id="aff2">
          <label>2</label>
          <institution>Vrije Universiteit Amsterdam</institution>
          ,
          <addr-line>De Boelelaan 1105, 1081 HV Amsterdam</addr-line>
          ,
          <country country="NL">The Netherlands</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2024</year>
      </pub-date>
      <volume>2</volume>
      <fpage>6</fpage>
      <lpage>28</lpage>
      <abstract>
        <p>Ontologies, vocabularies, and thesauri provide a shared conceptualisation for a domain. Manually maintaining and updating such knowledge systems when knowledge changes, does not scale for large domains, such as in biomedicine. Recently, large language models (LLMs) have been increasingly used as tools in knowledge engineering processes, ofering new possibilities for the automatic creation and maintenance of knowledge systems. This work explores how LLMs can be leveraged for the automated extension of such knowledge systems. Specifically, we build on the DRAGON-AI framework, which integrates Retrieval-Augmented Generation (RAG) to provide LLMs with access to external knowledge sources for more faithful outputs. We investigate the ability of the framework to predict relationships between a given knowledge system and a novel concept. We do so for both an ontology and a thesaurus, and analyse the impact of (i) enriching prompts with contextual information as well as more clear instructions, (ii) an alternative retrieval approach, and (iii) using a conversational model versus an instruction-following model. The results show superior quality in the ontology generations for all models and approaches compared to the thesaurus. The two models show varied performance across the diferent experiment configurations with only the conversational model showing notably improved performance, in terms of F1, for the ontology with the custom retrieval approach.</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In the field of Artificial Intelligence (AI), ontologies [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] and thesauri are used to explain and represent
formal knowledge for a specific domain. These structured representations can capture human knowledge
in a way that computers can process and interpret. They depict the concepts and relations of a shared
conceptualisation in a structural way [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Many information retrieval applications depend on the
accuracy of these knowledge systems, since they contain domain knowledge which is vital for the
correct and eficient functionality of these applications. The increasing complexity of intelligent systems
renders the use of an up-to-date knowledge system imperative [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], however manually creating and
updating such structures with the help of domain experts can be both time-consuming and costly [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
Moreover, techniques for constructing such knowledge structures, such as ontologies, in an automatic
manner that do not utilise a large language model (LLM), usually require the structure’s schema to be
predefined–a non-trivial task–as well as domain experts to process and evaluate the results [
        <xref ref-type="bibr" rid="ref5 ref6">5, 6</xref>
        ].
      </p>
      <p>
        LLMs [
        <xref ref-type="bibr" rid="ref7 ref8">7, 8</xref>
        ] constitute the state-of-the-art in the NLP domain due to their advanced capabilities in
language understanding [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]. Their integration in Knowledge Engineering (KE) workflows shows a
promising direction in automating the construction and extension of knowledge-holding structures. A
successful blend of LLMs and KE is evident in [
        <xref ref-type="bibr" rid="ref10 ref11">10, 11</xref>
        ], where authors use a language model to extract
information from unstructured text and in combination with a domain-specific ontology, they were
able to populate a knowledge graph in an automated fashion. In [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ] the authors built an ontology
(L. Stork)
      </p>
      <p>CEUR</p>
      <p>
        ceur-ws.org
by first feeding competency questions (CQs) in a language model, and then instructing the model to
extract relevant concepts and relationships. By using the model’s output suggestions, they are able
to successfully integrate them into an ontology. Nevertheless, LLMs also sufer from hallucination
problems [
        <xref ref-type="bibr" rid="ref13 ref14">13, 14</xref>
        ] which means that they show a tendency of creating their own fabricated content that
is not in-line with the ground truth.
      </p>
      <p>
        Retrieval-Augmented Generation (RAG) is an emerging technology that aims to reduce hallucinations
in LLMs by including external knowledge into the prompts [
        <xref ref-type="bibr" rid="ref15 ref16">15, 16</xref>
        ]. The RAG architecture usually
consists of an LLM with its own parametric memory, as well as an external data source (e.g. a vector
database) that is supplementing the LLM with additional information in order to enrich the prompt
with more relevant and accurate knowledge. This approach is known for its speed and cost-eficiency,
making it a preferred approach for connecting an LLM to proprietary data and providing responses
that are grounded to the data. [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ] shows an example of an efective utilisation of the RAG approach
to reduce hallucinations. By providing the LLM relevant information along with the user query, the
authors are able to mitigate the phenomenon of hallucinations. Almanac [
        <xref ref-type="bibr" rid="ref18">18</xref>
        ] is a RAG-infused LLM
framework that uses external tools such as search engines and medical databases. The evaluation of
this approach on 130 clinical questions shows that it achieves superior performance on the factuality
and accuracy of the responses, compared to an LLM that does not utilise the RAG architecture.
      </p>
      <p>This work further explores the capabilities of LLMs in combination with the RAG to automatically
construct knowledge systems (ontologies and thesauri) from textual data. We will leverage the
DRAGONAI framework [19], that utilises a RAG architecture, and evaluate its ability on relationship properties
generation. Our approach will test and measure the completeness and accuracy of the generated
relationship properties by exploring the efectiveness of various techniques within the
DRAGONAI framework. We will extend the framework by implementing a customised approach that could
potentially yield better results than the already existing approach. We also measure the performance
of the task of relationship generation on diferent large language models. We aim to understand the
impact of RAG for the task of ontology and thesaurus extension, and specifically:
RQ.1 Ontologies versus Thesauri. How efectively does a RAG system perform in the task of extending
ontologies, with complex, heterogeneous schema, versus extending thesauri with predefined, simpler
schema?
RQ.2 LLM-type. Which type of LLM (conversational or instruction-following) is more efective in the
tasks of ontology and thesaurus extension via RAG?
RQ.3 Prompting and Retrieval. How do variations in retrieval algorithms and prompt structures impact
the efectiveness of RAG for ontology and thesaurus extension?
The code for reproducibility of the experiments can be accessed through our GitHub repository1.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Related Work</title>
      <p>Automatic Thesaurus Generation Although available research on creating thesauri in an
automated manner is scarce, we can identify some specific approaches that ofer a promising guiding
principle. In [20] the authors use parallel corpora to create a bilingual thesaurus. By leveraging multiple
methodologies, such as morphological analysis, part-of-speech (POS) tagging, and statistical weighting,
they are able to generate a large number of thesaurus entries. Despite this fruitful endeavour to create
the bilingual thesaurus, a major problem arises when words or phrases in one language do not have a
direct equivalent in the other language. More advanced techniques could help alleviate this issue due to
their ability to capture the relationships between languages in a more optimal way. [21] proposes a
statistical method that incorporates syntactic parsing along with word co-occurrence to understand
the relationships between the word in a large number of medical abstracts. Although the thesaurus
1https://github.com/Antonis-Georgakopoulos/curate-gpt
produced from this approach contains an adequate number of entries, more advanced techniques could
help in discovering more complex semantic relationships between words that usually demand a deeper
understanding of the words’ meaning and the context.</p>
      <p>Rule-based and Statistical OL The Ontology Learning (OL) field tries to implement a variety
of diferent techniques and approaches for automatically creating an ontology from text [ 22]. It
accomplishes that by interpreting the intent and context behind data and not just processing it as
raw information. Before the use of deep neural networks, the field of OL heavily relied on the more
traditional machine learning (ML) techniques that include statistical and rule-based methods [23, 24, 25].
In [26] the authors utilised data mining techniques and heuristic-based approaches to generate an
ontology from domain-specific text. The approach mentioned in [ 27] utilised POS taggers as well
as syntactic parsers to expand ontologies by parsing unstructured text. Various works incorporate
the identification of lexico-syntactic patterns as part of the pipeline for efective OL implementations
[28, 23]. The Text2Onto framework [29] is able to perform the task of automatic ontology creation
by performing NLP techniques to identify taxonomies and other linguistic classifications from text.
Although these approaches provide an easy and transparent way to construct an ontology, they lack
the ability to generalize their performance to unseen data patterns and they are time-consuming due to
their dependency on human intervention [30].</p>
      <p>Deep Learning-based OL Deep learning (DL) approaches have shown improved performance on
specific NLP tasks compared to the more traditional ML approaches [ 31]. These methods are more
capable of creating word embeddings, understand the dependencies between words in a longer sequence
of text and extract concepts and relationships in a more eficient way. A plethora of academic literature
appears to utilise deep neural networks for the task of Entity Recognition (ER) in order to extract
specific entities from the unstructured text [ 32, 33]. In [34] the authors implemented a DL algorithm
based on an unsupervised neural network architecture in order to classify the taxonomic relationships
in the ontology. A combination of Gated Recurrent Units (GRU) and Long Short Term Memory (LSTM)
was utilised in [35] for the task of Named Entity Recognition (NER) in order to extract the ontological
concepts from text. Another hybrid model was proposed by [36] where they fused a Bidirectional
LSTM with a Recurrent Neural Network (RNN) so that they could analyse the input text data in both
directions. Despite the benefits that these approaches ofer over the more traditional ML techniques,
they require a high level of expertise for the training of deep learning models and may encounter
dificulties understanding more domain-specific terminology [ 37].</p>
      <p>
        LLM-based OL Due to the novelty of this area, existing research about the use of LLMs for
automatically extending ontologies or thesauri is limited. One study explores zero-shot prompting for ontology
extension across diverse knowledge domains and found that, while LLMs show potential, they still
require task-specific fine-tuning for more practical use, as it significantly improves performance across
all tasks [38]. In [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], the authors extract hierarchical concepts, based on a given query concept, by
prompting the LLM to return relevant subconcepts. Even though results show promise, hallucinations
occur, polluting generation results. To address these issues, the DRAGON-AI framework [19] explores
the impact of RAG for ontology generation, aiming to minimising hallucinations. The authors test
their approach on the task of ontology term completion. By providing a small free-text definition of a
novel concept, their approach aims to automatically extend the ontology with that concept. Overall,
the quality of the AI-generated ontology definitions was inferior compared to those constructed by
human experts, showing that human expertise is often still crucial for validation. Our approach
employs the DRAGON-AI framework to understand better how such models deal with the complexity of
ontologies versus thesauri, the efect of a novel retrieval approach, and the impact of diferent LLM
types, specifically those trained to follow instructions, versus those trained for conversation.
      </p>
    </sec>
    <sec id="sec-3">
      <title>3. Problem Definition</title>
      <p>Ontology extension This work explores the problem of extending an ontology with novel classes.
An ontology  is a formal representation of knowledge within a domain, typically defined as a tuple:
 = (, ,  ,  , ) where  is the set of concepts (or classes) representing entities in the domain, 
is the set of relations between these concepts,  is the set of individuals (or instances) representing
specific entities,  is the set of properties (or attributes) that describe characteristics of the concepts and
individuals, and  is the set of axioms that enforce logical constraints and define relationships between
concepts, individuals, and properties.</p>
      <p>The concept of ontology extension in this paper refers to the enrichment of an existing ontology
 : given a novel unseen concept or query term  ∈  ′, we predict target relations   ∈  and target
concepts   ∈  that relate the query term   to  . Thus, the task is to predict (  ,   ), given   . In this
work, for thesauri the task difers only for  , which consists of a fixed set of relationships: hierarchical
and associative relations.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Overview of the RAG architecture</title>
      <p>To answer our RQs, we employ the DRAGON-AI framework, which is based on the CURATE-GPT2
project. The RAG architecture consists of three main components: a generative model (an LLM), a
retriever, and a vector database (see Figure 1). The vector database contains extracted embeddings from
the primary and secondary data sources, while the retriever performs a nearest-neighbour similarity
search to retrieve the most relevant documents from the vector database. The generative model is
responsible for predicting, given query term   ∈  ′, target relations   ∈  and target concepts   ∈  .</p>
      <p>The retriever will extract data from the vector database in two diferent phases depending on the
methodological approach that is going to be used. During the first phase, which is mandatory across
all approaches in our research, the retriever will gather examples from the primary data source used,
that is essential for providing to the LLM a comprehensive understanding of the knowledge system’s
schema. The second phase, which is optional, involves retrieving examples from secondary data sources
that can be used to further improve the quality of the generated LLM responses. We refer to these
secondary data sources with  (background knowledge).
2https://github.com/monarch-initiative/curate-gpt</p>
    </sec>
    <sec id="sec-5">
      <title>5. Experimental Methodology</title>
      <sec id="sec-5-1">
        <title>5.1. Experimental Setup</title>
        <p>To adequately address the RQs presented in this paper, we will conduct multiple experiments with
various combinations of the knowledge systems, generative models, and methodological approaches. A
detailed summary of the combinations can be seen in Table 1. For each knowledge system (thesaurus
and ontology, RQ.1) we will employ two diferent LLMs ( RQ.2) and for each such combination we will
test the efect of three diferent methodological approaches ( RQ.3). The following sections describe
the diferent parts that synthesise the final methodological and architectural approach of this work. In
Section 5.2 we outline the distinct characteristics of the two main data sources used in this work, while
in Section 5.3 we present the diferent LLMs that generate the relations. Section 5.4 details the diferent
strategies used to evaluate the quality of the generated relations.</p>
      </sec>
      <sec id="sec-5-2">
        <title>5.2. Knowledge Systems</title>
        <p>To ensure insightful results from the experiments and explore RQ.1, we reviewed various ontologies
and thesauri to identify those that contained a suficient diversity of relationships. Our choices are
detailed below.</p>
        <p>Thesaurus The first data source for our experiments is the ELSST (European Language Social Science
Thesaurus) [39]. The ELSST thesaurus is a multilingual thesaurus for the social sciences, developed by
CESSDA and its national service providers. ELSST covers core social science aspects such as politics,
sociology, economics, and education, and contains 3422 concepts in total. ELSST contains the following
relationships:
1. broader: Indicates the concept that is more general than the current term. For the central
government entity the broader concept is government.
2. narrower: Specifies the scope of the current term and provides a subcategory. For the central
government entities such as coalition government and minority government are narrower concepts.
3. related: This is an entity that is related to the current term in a non-hierarchical manner. For
example, bureaucracy is a concept related to the central government.</p>
        <p>In Table 2 we can see the number of occurrences for each relationship property in the ELLST thesaurus.
Ontology The second data source is an ontology, namely the BioAssay Ontology (BAO) [40]. The
BAO ontology contains 8043 concepts and was chosen due to its plethora of diverse relationships
and concepts. The BAO ontology contains the descriptions of various chemical biology experiments
and their results. Table 3 shows the number of occurrences for each distinct relationship in the BAO
ontology.</p>
      </sec>
      <sec id="sec-5-3">
        <title>5.3. Large Language Models</title>
        <p>To efectively address RQ.2, we have chosen to compare the GPT-3.5-TURBO with the
GPT-3.5-TURBOINSTRUCT LLMs, developed by OpenAI. The GPT-3.5-TURBO model [41] is optimised for a variety of
natural language understanding tasks such as machine translation and natural language inference. As a
result, this kind of model is well suited for tackling problems that involve text generation.</p>
        <p>The GPT-3.5-TURBO-INSTRUCT model 3 is a specific variation of the GPT-3.5-TURBO model that is
trained to follow instructions. This model uses techniques, such as in-context learning, to understand a
given instruction. The GPT-3.5-TURBO-INSTRUCT model appears promising for our work, as our task
depends on specific instructions being followed correctly.
3https://platform.openai.com/docs/models/gpt-3-5-turbo</p>
      </sec>
      <sec id="sec-5-4">
        <title>5.4. Prompting and Retrieval</title>
        <p>To address RQ.3, we will run three diferent approaches based on varying retrieval and prompting
approaches. Below, we discuss the prompt engineering and retrieval variations, after which we detail
how these are employed in the three distinct approaches.</p>
        <p>Prompt Engineering LLMs show a tendency to hallucinate responses, as mentioned in Section 1. To
tackle this issue and optimise the performance of the tested LLMs, it is essential that we provide the
models with a well-constructed prompt that meets the specific requirements for our task. Although the
CURATE-GPT framework already uses a prompt that instructs an LLM to generate content according
to a set of examples, we aim at optimising the prompt for ontology extension task. As a result, we
deemed it necessary to construct a new prompt that clearly specifies the requirements for generating
relationships without over-extending the context of the prompt. The new prompt can be found in our
GitHub repository4.</p>
        <p>Retrieval Method Continuing with the exploration of techniques that could potentially enhance
the quality of the generated outputs, we decided to implement a diferent retrieval methodology. The
DRAGON-AI framework uses the Maximal Marginal Relevance (MMR) algorithm [42] to retrieve text
from the vector database, balancing diversity and relevance of the retrieved results, thus reducing
redundancy of the results. While the methodology ofers accurate results, we believe that a more
dedicated approach would improve the outcomes of our task. To accurately generate the relationship
properties for a query term, the LLMs have to understand the connections between all terms in the
structure. To enrich the prompt with relevant background knowledge  containing information about
the query term and other relevant terms, the secondary data sources should be searched with a query
term that is a combination of the main query term and the retrieved examples. These retrieved examples
are the most relevant terms to our main query term and we believe that these will form the majority
of the relationships. For example, if the main query term is famine and the retrieved example entities
include: hunger, infant feeding, forged migration etc., then we will generate query pairs such as: famine
hunger, famine infant feeding, famine forged migration, etc. By querying the secondary data sources
with these word combinations, we hypothesise that the discovery of parts of text that contain both
terms increases. The models can then infer the relationship between these terms according to the
context of the passage and their own parametric memory.</p>
        <p>Methodological Approaches The methodological approaches that we are going to follow are:
1. DRAGON-AI-NB approach: This approach does not utilise the background knowledge  part
of the RAG architecture for retrieving additional resources. It only provides the LLM with 10
examples from the tested ontology or thesaurus that are semantically similar to the query term.</p>
        <p>The plain DRAGON-AI-NB approach will be used as a baseline.
2. DRAGON-AI approach: This approach includes the full DRAGON-AI approach, including
supplementary background knowledge  which augments the prompt of the LLM with information
relevant to the query term. The retrieval algorithm used is based on the pre-existing CURATE-GPT
implementation.
3. DRAGON-AI-CUSTOM approach: This approach customises the DRAGON-AI approach by
adapting the methodology for retrieving examples from  as well as the prompting technique,
following the adaptations described above.
4https://github.com/Antonis-Georgakopoulos/curate-gpt/blob/main/assets/custom_prompt.txt</p>
      </sec>
      <sec id="sec-5-5">
        <title>5.5. Evaluation Metrics</title>
        <p>For all generated relationships of all the query terms in the test set (test set creation is described in
Section 5.6), we will calculate the true positives, false positives and false negatives, which we define in
the following way:
True positive : given   , the predicted target tuple (  ,   ) matches one from the test set.
False negative : given   , the predicted relationship tuple (  ,   ) does not exist in the test set.
False positive : none of the tuples ( ,   ) for   from the test set were predicted.</p>
        <p>These measurements can help us calculate several important evaluation metrics that can shed light on
the overall performance of the models in the task of ontology and thesaurus extension. These evaluation
metrics include precision, recall and F1 score. We opt for F1 over accuracy, due to the imbalanced nature
of the ontology and thesaurus.</p>
        <p>Apart from the evaluation mentioned above, we also follow two diferent approaches for evaluating
the generated relationships of an entity: a strict approach and a lenient approach. Both these approaches
penalise incorrect predictions in a diferent way.</p>
        <p>Lenient approach generated relationships that do not exactly match the gold standard relationships
but are valid by inference (via hierarchical or subsumption relationships) are not counted as
incorrect (0), but as partially correct (0.5). The inspiration of this evaluation method was drawn
from the approach that was followed in [19].</p>
        <p>Strict approach generated relationships that do not exactly match the gold standard relationships
but are valid by inference are counted as incorrect (0).</p>
      </sec>
      <sec id="sec-5-6">
        <title>5.6. Test Set Creation</title>
        <p>We create a test set for both the ELSST thesaurus and the BAO ontology to test the diferent approaches.
To ensure that there is no data leakage between the ontology  and the test set, we additionally perform
a postprocessing step that we describe below.</p>
        <p>Ontology and Thesaurus Partitioning For our experiments, we artificially create an ontology
extension  ′. We do so by removing tuples (  ,   ,   ) from the base ontology  , to serve as our test
set. For this, we analysed the distributions of both the ELSST thesaurus and the BAO ontology to
make sure that the predicate distribution of the extension is similar to the distribution of the remaining
base ontology. As can be seen in the Figure 2 below, these distributions do not follow a normal
distribution pattern. Consequently, we can use stratified sampling to extract a valid  ′ set. Stratified
sampling ensures that all subgroups withing the overall population are represented in the sample. By
proportionally representing each subgroup, the test set accurately reflects the overall population of
the initial dataset. Both the  ′ for the BAO ontology as well as for the ELSST thesaurus, contain 200
entities.</p>
        <p>Data Leakage First, we removed any reference to concepts from  ′. For each of the query terms  
contained in  ′, we iterated through  and removed every mention of that term. We followed the same
approach for the ontology and thesauri when used as secondary data sources.</p>
      </sec>
    </sec>
    <sec id="sec-6">
      <title>6. Results</title>
      <p>The following section presents results for the experiments (as outlined in Table 1). Both lenient and strict
evaluation methods were carried out as mentioned in Section 5.5. After conducting our experiments,
we did not find a significant diference between the two evaluation methods and therefore decided
to include only results for the strict evaluation. Results of the lenient evaluation can be found in our
GitHub repository1.
6.1. ELSST</p>
      <sec id="sec-6-1">
        <title>6.1.1. Results for the ELSST Thesaurus</title>
        <p>Table 4 provides a summary of the results for the ELSST thesaurus. We additionally provide the number
of total generated relationships for each approach. To answer RQ.2 by comparing the performance
that each model exhibits in generating relationships for the ELSST. From the table 4, we can observe
that for the GPT-3.5-TURBO model the DRAGON-AI-NB approach achieves a moderate number of true
positives and false negatives, resulting in a more balanced F1 score. In contrast, for the same approach,
the instruction-following model yields fewer true positives and higher false positives, leading to worse
overall performance for the same approach. A similar pattern can be observed for the
DRAGON-AICUSTOM approach as well, where every evaluation metric for the conversational language model
shows a higher value. For the DRAGON-AI approach the results demonstrate an opposite scenario,
where the GPT-3.5-TURBO-INSTRUCT model performs better across every evaluation setting. The
results on table 4 along with the graphical representation of the outcomes in Figure 3, suggest that
the GPT-3.5-TURBO model generally achieves higher scores in diferent configuration approaches
compared to the GPT-3.5-TURBO-INSTRUCT model.</p>
        <p>To address RQ.3, we will compare the performances of the diferent methodological approaches
for each LLM. Starting with the conversational model, the DRAGON-AI-NB approach appears to be
more balanced compared to the other two approaches. This methodological approach also yields a
higher precision score, which logically follows from the fact that the approach generates less overall
relationships and as a result we have fewer false positive cases. A related trend can be observed for the
GPT-3.5-TURBO-INSTRUCT model where the DRAGON-AI-NB approach shows higher F1 score and
precision values. However, the recall score is comparatively lower than that of the other two approaches,
showing a limitation in predicting the gold standard label data. For predicting the maximum number of
true positive cases, the DRAGON-AI-CUSTOM approach is the most efective for both models, due to
the large number of relationships that it generates. Overall, the DRAGON-AI-NB approach appears to
be the most promising methodology for every LLM for the ELSST.</p>
      </sec>
      <sec id="sec-6-2">
        <title>6.1.2. Performance Comparison by Predicate Type</title>
        <p>By looking at Figure 4 it is evident that both models perform the worst, looking at the narrower
predicate due to the low precision, recall and F1-score values. This means that the models are unable to
correctly predict most of the golden standard (  ,   ,   ) tuples where   = narrower. For test examples
where   = related there is great variability in the metrics for all three approaches with the
DRAGONAI-CUSTOM approach appearing to be the most balanced. The broader predicate demonstrates the
most harmonious performance due to the higher F1 score across all methodological approaches.</p>
        <p>Comparing the results from the two models, the broader predicate appears to be the most accurately
generated and thus more easily comprehended by the two models, resulting in greater accuracy when
linking concepts with that specific predicate. When we observe the related predicate we can detect that
it almost always produces the lowest precision scores in every methodology. This could be attributed
to the fact that the majority of the generated predicates belong to the related relationship type. If we
examine a part of a prompt that we provide to the LLM, we can indeed observe that for the examples
that were given to the model, the majority of the relationship types contained in the examples are of
type related. As a result, the models could exhibit a bias towards generating this specific relationship
type more than any other relationship type.
6.2. BAO</p>
      </sec>
      <sec id="sec-6-3">
        <title>6.2.1. Results for the BAO Ontology</title>
        <p>This section provides an analysis of the results obtained from our experiments performed on the BAO
test set. To investigate RQ.2 we examine the performance of each LLM on every methodological
approach. Looking at table 5 as well as Figure 5, both the DRAGON-AI-NB and DRAGON-AI approaches
show a similar pattern in the outcome of the prediction task with the F1 score and recall values for
both approaches being greater for the instruction-following model. Both approaches return a higher
amount of true positive cases compared to the conversational model. However, the GPT-3.5-TURBO
model exhibits a lower number of false positive cases, therefore managing to outperform the
GPT-3.5TURBO-INSTRUCT model in terms of the precision metric. Looking at the DRAGON-AI-CUSTOM
approach, it is evident that the GPT-3.5-TURBO model yields a comparatively better performance than
the GPT-3.5-TURBO-INSTRUCT model. The latter generally achieves more optimal performance when
being supplied with a more minimal prompt, whereas GPT-3.5-TURBO performs best when the prompt
is supplemented with additional information.</p>
        <p>Shifting our attention to RQ.3, it is undeniably clear that for the GPT-3.5-TURBO model, the
DRAGONAI-CUSTOM approach achieves the best performance across every methodology used. Not only it
manages to generate the most amount of true positive cases, but also it shows the lowest amount of
false negative cases. This indicates that the utilisation of this approach was able to generate a big
proportion of relationships that belong in the golden standard data and the methodology was perfectly
complimented by the conversational model. For the instruction-following model, both DRAGON-AI-NB
and DRAGON-AI approaches show a similar performance that is superior to that of the
DRAGON-AICUSTOM approach.</p>
      </sec>
      <sec id="sec-6-4">
        <title>6.2.2. Performance Comparison for the subClassOf Predicate</title>
        <p>The analysis of the results for the predicate subClassOf can help us discover any potential hidden
pattern in the way that models generate the relationships that contain this specific predicate. This stems
from the fact that the subClassOf predicate is the most common relationship type in the BAO. As seen
in the Figure 6, the result patterns for the subClassOf predicate appear to be almost identical to the ones
for the overall test set. The combination of the GPT-3.5-TURBO model with the DRAGON-AI-CUSTOM
approach appears to constitute the most balanced option with an F1 score that is a lot higher than
any other approach. For both models the DRAGON-AI-CUSTOM approach appears to be generating
comparatively the greatest proportion of the golden standard data, out of the three approaches, due to
the higher recall value. Nevertheless, the DRAGON-AI-CUSTOM approach does not perform as well for
the GPT-3.5-TURBO-INSTRUCT model, as was also observed in the evaluation of the overall test set.</p>
      </sec>
    </sec>
    <sec id="sec-7">
      <title>7. Discussion</title>
      <p>In this section, we will reflect on the results that we obtained from our experiments and try to address
each research question, providing an analysis of the possible answers.</p>
      <p>RQ.1 Judging from the results that stem from the experiments that we conducted, we can observe
that both LLMs that were tested seem to be performing better on the ontology extension task than the
thesaurus extension task. This becomes evident when we notice the prominent diference between
the F1 scores for the ontology and the thesaurus (regardless of the approach used). One inference that
can be made from these results is that when we are testing a structure that contains a predicate that is
significantly more prevalent than others, the models show a more advanced capability of predicting the
golden standard relationships regarding this specific predicate. On the other hand, when the predicates
are more evenly distributed in terms of their occurrences in the dataset, the models yield comparatively
lower performance. As a result, it can be asserted that the models become slightly more biased in
predicting the most common predicates.</p>
      <p>It is important to note that for ontologies with greater variability and distribution, the results could be
diferent. It is necessary to further evaluate the three approaches tested (DRAGON-AI-NB, DRAGON-AI
and DRAGON-AI-CUSTOM) with additional knowledge structures.</p>
      <p>RQ.2 Results for RQ.2 are inconclusive. For the ELSST thesaurus, if we would like to have the
most balanced approach, we would choose the GPT-3.5-TURBO model and utilise the DRAGON-AI-NB
approach. In a case that we want to provide additional context into the prompt, it is evident that
the GPT-3.5-TURBO model with the DRAGON-AI-CUSTOM approach is the best combination. The
GPT-3.5-TURBO-INSTRUCT appears to be beneficial only when we follow the DRAGON-AI approach.</p>
      <p>For the BAO ontology, it is clear that the GPT-3.5-TURBO model combined with the
DRAGON-AICUSTOM approach gives us the best overall performance. The same model should be chosen in a
scenario where we would like to minimise the amount of false positive cases that the model generates.
However, in a situation where there is not additional context available for enriching the prompt, then
the GPT-3.5-TURBO-INSTRUCT model becomes a better overall choice.</p>
      <p>We identify a weakness of the GPT-3.5-TURBO-INSTRUCT model when handling a plethora of
diverse data. Although the DRAGON-AI-CUSTOM approach contains a prompt with specific steps for
the model to follow, it appears that the GPT-3.5-TURBO-INSTRUCT model does not perform as well in
understanding the task as well as separating the diferent sections of the prompt. On the other hand,
the GPT-3.5-TURBO model seems to benefit more from the instructions given in the prompt and does
not face dificulties regarding the additional context that we provide in the prompt. Thus, it becomes
clear that if we would prefer to enrich the prompt with extra information, then the GPT-3.5-TURBO
model is the better choice, while the GPT-3.5-TURBO-INSTRUCT model should be chosen when the
prompt is relatively short but contains detailed instructions.</p>
      <p>The results from [19] further validate our findings with respect to the ontology structures. In the paper
the authors observed a weakness of the Nous-Hermes-13b model, which was fine-tuned over a plethora
of instructions, to predict the relationships of various ontologies as accurately as the GPT-3.5-TURBO
model.</p>
      <p>RQ.3 The results suggest that for the GPT-3.5-TURBO model, the DRAGON-AI-CUSTOM approach
always yields more accurate outcomes than the DRAGON-AI approach for both the ELSST and the BAO
ontology. This means that a properly structured prompt with clear instructions and a more diverse
context is beneficial for that specific model. Conversely, for the GPT-3.5-TURBO-INSTRUCT model,
methodologies that use a more minimal prompt and less diverse context appear to be more overall
balanced. To provide a more complete answer, one additional evaluation to perform would be to test
both models with minimal additions for each experiments. For example, we could conduct experiments
with more minimal prompts and only a single source of additional data (e.g. PDF files) to get a more
comprehensive evaluation.</p>
    </sec>
    <sec id="sec-8">
      <title>8. Conclusion</title>
      <p>Enriching ontologies and thesauri with relationships that were generated from large language models
is a challenging task and requires multiple resources and diferent models regarding the algorithmic
approach that is being followed. We tested one ontology (BAO) and one thesaurus (ELSST) with two
diferent LLMs and three distinct methodologies in order to understand the strengths and weaknesses
of each approach and each model. We extended the functionalities of the CURATE-GPT framework in
order to develop a customised approach of extracting relevant data from the vector database. As the
additional data that enriches the prompts, we utilised various data sources so that we could introduce
further diversity in the context of the prompt. Moreover, we enhanced the prompt of the
CURATEGPT framework with a more directive prompt that contains clear steps for the task of relationships
generation.</p>
      <p>The experiments yielded varied results, showing that there is no clear answer as to what model and
approach performs best, as it depends highly on the specifications of each approach. Our customised
approach in combination with one specific model appears to be the most beneficial for the generation
of the relationship properties for the ontology. Studies such as these, that aim at getting a better
understanding of the use of LLMs and RAG systems for knowledge engineering tasks, are important for
better development and reuse of ontologies. Manually updating ontologies or thesauri does not scale for
large domains (such as biomedicine), resulting in ontologies that are not up-to-date and limiting reuse.</p>
    </sec>
    <sec id="sec-9">
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