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  <front>
    <journal-meta>
      <issn pub-type="ppub">1613-0073</issn>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>mender Systems?⋆</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Dario Di Palma</string-name>
          <email>dario.dipalma@poliba.it</email>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Giovanni Servedio</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Vito Walter Anelli</string-name>
          <email>vitowalter.anelli@poliba.it</email>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Giovanni Maria Biancofiore</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Fedelucio Narducci</string-name>
          <email>fedelucio.narducci@poliba.it</email>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Leonarda Carnimeo</string-name>
          <email>leonarda.carnimeo@poliba.it</email>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Tommaso Di Noia</string-name>
          <email>tommaso.dinoia@poliba.it</email>
        </contrib>
        <contrib contrib-type="editor">
          <string-name>ChatGPT, Recommender Systems, Evaluation, Re-ranking</string-name>
        </contrib>
      </contrib-group>
      <abstract>
        <p>Large Language Models (LLMs) have recently demonstrated impressive capabilities across a range of natural language processing tasks. Notably, ChatGPT has exhibited superior performance in numerous tasks, particularly under zero and few-shot prompting conditions. Motivated by these successes, the Recommender Systems (RS) and Information Retrieval research communities have started exploring the potential applications of ChatGPT in recommendation and information filtering scenarios.</p>
      </abstract>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>-</title>
      <p>CEUR
ceur-ws.org</p>
    </sec>
    <sec id="sec-2">
      <title>1. Introduction</title>
      <p>The rapid increase in human-generated data, particularly unstructured text, has significantly
transformed the digital world. The World Wide Web now serves as a vast repository of
diverse information, representing both individual and corporate needs, opinions, and knowledge.
However, extracting value from this immense resource remains a major challenge.</p>
      <p>
        Addressing this challenge involves the use of Natural Language Processing (NLP) techniques.
NLP encompasses a range of computational methods [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] designed to analyze, interpret, and
derive meaning from natural language. By employing these techniques, professionals across
ifelds like data science, IT, marketing, and social research can tap into the potential of this
extensive unstructured data.
      </p>
      <p>
        The ease of sharing and accessing information has significantly increased the speed of
information dissemination, but it also brings concerns such as information overload (e.g. [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]),
and issues related to quality, privacy, and security.
      </p>
      <p>
        Various methods, including Information Retrieval (IR) [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] and Recommender Systems (RSs) [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ],
are designed to sift through large datasets to find valuable information. However, their success
largely depends on eficiently filtering out irrelevant or low-quality content to ensure that users
can quickly find reliable and pertinent information.
      </p>
      <p>IR systems have integrated advanced NLP techniques like semantic analysis and natural
language understanding to provide contextually relevant information beyond simple keyword
matching, allowing for a deeper understanding of user queries.</p>
      <p>
        Recommender Systems have also advanced in predicting user preferences and delivering
personalized content recommendations [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]. By analyzing past behaviors, interactions, and
preferences, RSs curate content that aligns with individual tastes. Incorporating NLP techniques
in RSs enhances their ability to capture user preferences with greater detail, resulting in highly
relevant recommendations.
      </p>
      <p>
        Additionally, recent research [
        <xref ref-type="bibr" rid="ref6 ref7 ref8">6, 7, 8</xref>
        ] underscores the benefits of interactive systems in
improving the quality and relevance of information and enhancing user satisfaction and
experience [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]. These systems, through human-like dialogues, can retrieve more precise data tailored
to individual preferences, leading to a more personalized user experience.
      </p>
      <p>
        This shift towards conversational interfaces has fueled the rise of digital assistants like Amazon
Alexa, Google Assistant, Microsoft Cortana, and Apple Siri [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. Their ability to understand
and process natural language queries in real-time has revolutionized user interaction with
technology, making information access more intuitive and eficient.
      </p>
      <p>
        The development of advanced Language Models, particularly Large Language Models (LLMs)
like Generative Pre-trained Transformer 3 (GPT-3) [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ], has greatly enhanced interaction with
digital systems [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ], enabling unprecedented access to information through natural language
queries.
      </p>
      <p>These models represent a new era in machine comprehension and language generation,
allowing for conversations with remarkable naturalness and depth. Their capabilities go beyond
simple query processing, enabling dynamic and nuanced dialogues similar to human interactions.</p>
      <p>
        While GPT-3 has shown significant advancements in generating human-like text, the
introduction of ChatGPT on November 30, 20221, marked a milestone with an AI model capable of
engaging in dialogue like never before, covering a wide array of tasks [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. Researchers are
keenly exploring ChatGPT’s potential across various applications, particularly in
recommendation tasks [
        <xref ref-type="bibr" rid="ref13 ref14 ref15 ref16">13, 14, 15, 16</xref>
        ].
      </p>
      <p>
        While there is increasing interest in integrating ChatGPT with recommender systems to
improve accuracy [
        <xref ref-type="bibr" rid="ref17 ref18">17, 18</xref>
        ] or fairness [
        <xref ref-type="bibr" rid="ref19 ref20">19, 20</xref>
        ], some areas, such as the system’s ability to re-rank
item lists, remain under-explored.
      </p>
      <p>
        We investigate the performance of ChatGPT-3.5 and ChatGPT-4 in recommendation tasks
under a zero-shot role-playing prompt condition. This approach allows us to evaluate these
models’ efectiveness as re-rankers in three diferent domains: Books, Movies, and Music (using
datasets like Facebook Books [
        <xref ref-type="bibr" rid="ref21">21</xref>
        ], MovieLens [
        <xref ref-type="bibr" rid="ref22">22</xref>
        ], and Last.FM [
        <xref ref-type="bibr" rid="ref23">23</xref>
        ]).
      </p>
      <p>Moreover, since ChatGPT is a Large Language Model and not a dedicated Recommender
System, we explore its ability to suggest items by comparing its recommendation lists with
those generated by content-based, collaborative filtering, and hybrid recommenders. This
analysis aims to determine whether ChatGPT favors content-based or collaborative filtering
methods in its recommendation generation. The goal is to gain insights into the approach
ChatGPT mimics during the recommendation process.</p>
      <p>Our contributions can be summarized as follows:
• We evaluate the performance of ChatGPT-3.5 and ChatGPT-4 on re-ranking a list of
recommendations across three domains: Books, Movies, and Music.
• We investigate the underlying methodology employed by ChatGPT in generating
recommendations, aiming to understand whether the model demonstrates an inclination
towards content-based, collaborative, or hybrid recommenders to gain insights into its
recommendation process.</p>
    </sec>
    <sec id="sec-3">
      <title>2. Related Work</title>
      <p>
        Integrating Large Language Models (LLMs) into recommender systems has garnered significant
attention due to their powerful generative capabilities. However, much of the research in
this area remains preliminary. Notable examples include M6-Rec [
        <xref ref-type="bibr" rid="ref24">24</xref>
        ], which leverages the
M6 LM [
        <xref ref-type="bibr" rid="ref25">25</xref>
        ] for various recommendation tasks by framing the recommendation process as
a language understanding or generation task. Similarly, P5 [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ] uses personalized prompt
templates to integrate user-item information, enabling predictions in a zero-shot or few-shot
manner. These approaches, however, create ad-hoc solutions rather than directly utilizing
generic LLMs like ChatGPT.
      </p>
      <p>
        Wu et al. [
        <xref ref-type="bibr" rid="ref27">27</xref>
        ] employ LMs (e.g., BERT, GPT-2) and LLMs (e.g., T5, LLaMA) to address the
cold start issue, highlighting the critical role of prompt design. Building on this concept, our
research focuses on re-ranking items rather than recommending them individually. Zhang et al.
[
        <xref ref-type="bibr" rid="ref28">28</xref>
        ] fine-tune T5 for sequential recommendations, demonstrating comparable ranking abilities
to zero-shot methods like GPT-3.5.
      </p>
      <p>
        He et al. [
        <xref ref-type="bibr" rid="ref29">29</xref>
        ] conduct an empirical study on conversational recommendations using GPT-3.5,
GPT-4, and LLAMA, finding that LLMs outperform fine-tuned Conversational Recommender
System (CRS) models. Kang et al. [
        <xref ref-type="bibr" rid="ref30">30</xref>
        ] show that zero-shot LLMs can be cost-efective compared
to fine-tuned models, prompting further exploration of ChatGPT’s ranking capabilities.
      </p>
      <p>
        Early work by Zhang et al. [
        <xref ref-type="bibr" rid="ref31">31</xref>
        ] used GPT-2 for session-based recommendations, showing
that pre-trained LM-based methods can perform well in zero-shot settings. Recent studies, such
as GPT4Rec by Li et al. [
        <xref ref-type="bibr" rid="ref32">32</xref>
        ] and Wang and Lim [
        <xref ref-type="bibr" rid="ref33">33</xref>
        ], indicate that LLMs can efectively handle
recommendation tasks through strategic prompting.
      </p>
      <p>
        ChatREC by Gao et al. [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ] introduced a ChatGPT-augmented recommender system using
interactive conversations to generate Top-N recommendations.
      </p>
      <p>
        Hou et al. [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ] explored ranking tasks with LLMs in zero-shot settings, identifying position
bias issues in prompts. Sanner et al. [
        <xref ref-type="bibr" rid="ref34">34</xref>
        ] assessed LLM-based RS abilities for Top-N
recommendations, highlighting the efectiveness of zero-shot settings in cold-start scenarios. Li et al.
[
        <xref ref-type="bibr" rid="ref35">35</xref>
        ] developed BookGPT for book recommendations, using Role-Play prompting to achieve
accuracy comparable to baselines, although their focus was limited. Dai et al. [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ] examined
ChatGPT’s performance in various recommendation tasks, showing balanced performance
in non-rating tasks. Xu et al. [
        <xref ref-type="bibr" rid="ref36">36</xref>
        ] confirmed the efectiveness of Role-Playing prompting in
zero-shot scenarios for LLM-based RSs, focusing on accuracy.
      </p>
      <p>Our work is the first to investigate re-ranking capabilities, examining ChatGPT’s ability to
generate lists similar to content-based and collaborative filtering methods.</p>
    </sec>
    <sec id="sec-4">
      <title>3. Experiments</title>
      <p>The following sections detail the methodology and experimental setup used in our research.
Specifically, Section 3.1 reviews the datasets employed and the necessary pre-processing steps to
comply with ChatGPT’s constraints. Section 3.2 presents the models used for similarity checks
and the experimental settings. Finally, Sections 3.3 and 3.4 discuss the results from evaluating
ChatGPT as a re-ranker and its similarity to other recommenders. Each experiment is designed
to address the following research questions:
RQ1. Can ChatGPT efectively re-rank and enhance recommendations by utilizing user history?
(Explored in Section 3.3)
RQ2. How closely do the recommendation lists generated by ChatGPT match those produced
by Collaborative Filtering and Content-based Recommender Systems? (Examined in
Section 3.4)</p>
      <sec id="sec-4-1">
        <title>3.1. Pre-processing Phase</title>
        <p>In the domain of Recommender Systems (RSs), the most common method to evaluate a model’s
performance is through ofline experiments using existing datasets, typically historical data or
logs. For our study, we utilized three well-known and publicly accessible datasets from diferent
domains: books, music, and movies.</p>
        <p>
          Specifically, we used the Facebook Books [
          <xref ref-type="bibr" rid="ref21">21</xref>
          ], Last.FM [
          <xref ref-type="bibr" rid="ref23">23</xref>
          ], and MovieLens [
          <xref ref-type="bibr" rid="ref22">22</xref>
          ] datasets.
Despite their popularity in literature, we had to consider the token limits of the ChatGPT API.
To accommodate this limitation, we applied specific preprocessing steps to adjust the user
interaction histories to the context length imposed by the API.
        </p>
        <p>Consequently, we adopted an iterative-10-core strategy on the users and items within the
datasets, retaining only those with at least ten occurrences. However, upon analyzing each
dataset, we found that some users’ interaction histories in MovieLens exceeded the maximum
context length. Therefore, additional preprocessing was necessary to reduce the number of
interactions. We set a threshold of 200 interactions to address the context constraints, resulting
in a modified MovieLens dataset.</p>
        <p>Table 1 presents the statistics of these datasets before and after preprocessing.
Here is a brief overview of each dataset:</p>
        <p>Facebook Books Dataset. The Facebook Books dataset2 was released for the Linked Open</p>
        <sec id="sec-4-1-1">
          <title>2https://github.com/sisinflab/LinkedDatasets/</title>
          <p>Dataset
MovieLens
Last.FM
FB Books
Data Challenge 20153 and covers the book domain. It includes implicit feedback and item-feature
mappings to DBpedia for each book, allowing the retrieval of data content such as book genres
and relevant author information.</p>
          <p>
            Last.FM Dataset. The Last.FM dataset contains user-artist play data from the Last.FM online
music system, released during the HETRec2011 Workshop4 [
            <xref ref-type="bibr" rid="ref23">23</xref>
            ]. It includes information on
social networking, tagging, artists, and music listening habits of 2000 users.
          </p>
          <p>
            MovieLens Dataset. The MovieLens dataset is widely used in the Recommender Systems
community [
            <xref ref-type="bibr" rid="ref22">22</xref>
            ]. Various versions are available5, but our study utilized the MovieLens 100k
version, which contains movie ratings on a 1-5 scale.
          </p>
        </sec>
      </sec>
      <sec id="sec-4-2">
        <title>3.2. Experimental Setting</title>
        <p>
          To conduct the experiments, we compared the performance of ChatGPT-3.5 and
ChatGPT4 models against state-of-the-art recommender systems. To ensure a fair comparison, we
conducted extensive Bayesian hyper-parameter optimization for each baseline to determine
the optimal configuration. For complete reproducibility, we utilized the Elliot recommendation
framework [
          <xref ref-type="bibr" rid="ref37">37</xref>
          ].
        </p>
        <p>The models used to evaluate ChatGPT against state-of-the-art recommenders are categorized
into Collaborative Filtering, Content-Based Filtering, and Non-personalized approaches:
• Collaborative Filtering: EASE [38], RP3 [39], ItemKNN [40], UserKNN [41],
Light</p>
        <p>GCN [42], MF2020 [43], NeuMF [44].
• Content-Based Filtering: VSM [45], AttributeItemKNN [46], AttributeUserKNN [46].
• Non-personalized Random Model, MostPop Model.</p>
        <p>The evaluation employs the all unrated items protocol [47, 48], where the set of
recommendable items for each user includes all items except those previously interacted with by the user.
The datasets are divided into training and test sets, with 80% of the user-item interactions used
for training and 20% reserved for testing.</p>
        <p>While the recommendation baselines can be implemented using the open-source Elliot
framework, generating recommendations from the ChatGPT models requires using the OpenAI
API. Specifically, for each user in each dataset, we craft a prompt to obtain a list of recommended
items.
3https://2015.eswc-conferences.org/program/semwebeval.html
4https://grouplens.org/datasets/hetrec-2011/
5https://grouplens.org/datasets/movielens/</p>
        <p>+0.127
+0.090</p>
        <p>+0.101</p>
      </sec>
      <sec id="sec-4-3">
        <title>3.3. Re-ranking Evaluation</title>
        <p>This section investigates ChatGPT’s potential to re-rank a list of recommendations, i.e., the
ability of a recommender to improve the quality of recommendations by adjusting the order in
which items are presented to the user [49].</p>
        <p>We defined two experimental conditions to assess ChatGPT’s re-ranking capability: (a) asking
ChatGPT to re-rank the most popular items in the datasets based on the user’s history, and (b)
asking ChatGPT to re-rank a pre-filtered list of suitable items for each user using a k-Nearest
Neighbors (k-NN) algorithm.</p>
        <sec id="sec-4-3-1">
          <title>Re-ranking Prompt</title>
          <p>Given a user, act as a Recommender System. You know that the user likes the following
items ordered by preference: {history of the user}. Re-rank this list of items into a top-50
recommendations: {list of items to re-rank}</p>
          <p>To conduct the experiments, we used a Role-Play Prompting approach [50] to query ChatGPT.
For condition (a), re-ranking the most popular items, we used the prompt shown above, ordering
the items from most to least popular. For condition (b), re-ranking the nearest neighbor
recommendations, we used the same prompt, but the item order was determined by the k-NN
algorithm.</p>
          <p>Building on these experimental conditions, this section aims to address the following research
question:</p>
          <p>RQ1. Can ChatGPT effectively re-rank and enhance recommendations by utilizing user history?
Figures 1a and 1b illustrate the performance of ChatGPT-3.5 and ChatGPT-4 models across
three domains: Books, Music, and Movies, compared to the Most Popular and k-NN methods.
Performance is evaluated using nDCG, a measure of ranking quality that accounts for both
the relevance and the position of items in the ranked list. Higher nDCG values signify better
performance in ranking relevant items higher.</p>
          <p>From the bar graphs, we can draw the following observations:
• Across all three domains, ChatGPT-4 consistently achieves higher nDCG scores than
ChatGPT-3.5 and the baseline methods, regardless of the experimental conditions. This
indicates that ChatGPT-4 is more efective at ranking items according to users’ preferences.
• The type of setting also influences the results. For the Most Popular items, shown in
Figure 1a, the MostPop baseline exhibits a lower nDCG due to insuficient user influence.
However, initial filtering using k-NN results in higher nDCG scores, indicating a step
towards personalization. Despite this, the ChatGPT models, particularly ChatGPT-4,
further enhance recommendation performance by better understanding user preferences.</p>
          <p>In summary, to address RQ1, we analyze the nDCG values and observe that ChatGPT’s
re-ranking improves recommendation performance, providing a positive answer. While the
study does not delve into the reasons behind this improvement, we hypothesize that it arises
from GPT’s extensive knowledge base and its ability to understand user preferences and the
relevance of items. Future research will focus on exploring the explainability of the deep
learning model behind ChatGPT and its eficacy in re-ranking recommendations. However, a
detailed explainability analysis is beyond the current study’s scope.</p>
        </sec>
      </sec>
      <sec id="sec-4-4">
        <title>3.4. Recommendation List Similarity</title>
        <p>This section examines the similarity between the recommendation lists generated by ChatGPT
and those produced by Content-based or Collaborative Filtering Recommender Systems (RSs)
using a role-play prompt defined below.</p>
        <sec id="sec-4-4-1">
          <title>Top-N Recommendation Prompt</title>
          <p>Given a user, as a Recommender System, please provide only the names of the top 50
recommendations. You know that the user likes the following items: {history of the user}
Our hypothesis is that ChatGPT will leverage content features of the items, but we also
suppose it will learn collaborative information during the training process. To validate this
hypothesis, we compare the similarity between these recommendation lists. Specifically, we
aim to answer the following research question:</p>
          <p>RQ2. How closely do the recommendation lists generated by ChatGPT match those produced by
Collaborative Filtering and Content-based Recommender Systems?</p>
          <p>To address this question, we use two types of metrics: the Jaccard Index [51], which measures
the size of the intersection between two sets of recommended items for each user, disregarding
the order of items, and Rank-biased Overlap (RBO) [52], which measures the similarity between
two ranked lists, considering the order of items.</p>
          <p>The results, presented in Tables 2, 3, and 4, are divided by domain. For each domain
and model, the average metrics are calculated on a per-user basis, highlighting the types of
recommender systems, namely Collaborative Filtering (CF) and Content-Based Filtering (CBF)
methods.</p>
          <p>For the Facebook Books dataset, ChatGPT-4’s recommendations show a high degree of
similarity with those of ChatGPT-3.5, followed by EASE ( ) , LightGCN( ) , and MostPop,
based on both Jaccard and RBO metrics. ChatGPT-3.5 also shows the highest similarity with
ChatGPT-4 and, similarly, shares similarities with EASE ( ) , LightGCN( ) , and MostPop. For
the Last.FM dataset, ChatGPT-4’s recommendations align closely with ChatGPT-3.5, followed
by MF2020( ) , ItemKNN( ) , and AttributeUserKNN( ) . While ChatGPT-3.5 shows a similar
pattern using the Jaccard metric, the RBO metric is led by RP3( ) and MF2020( ) , indicating a
diferent item ranking approach. For the MovieLens dataset, ChatGPT-4 shows unexpected
Jaccard similarity with EASE ( ) and MostPop, with ChatGPT-3.5 trailing behind. However,
the RBO metric reveals EASE ( ) as the most similar to ChatGPT-4, followed by ChatGPT-3.5.
ChatGPT-3.5’s lists show the highest similarity with those of ChatGPT-4 across both metrics,
followed by EASE ( ) and MostPop.</p>
          <p>Notably, the high mutual similarities between the ChatGPT models meet expectations.
However, their pronounced afinity with Collaborative Filtering recommenders supports our
hypothesis: GPT models’ proficiency extends beyond recognizing relevant content, encompassing the
ability to leverage latent collaborative information within these models.</p>
        </sec>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>4. Conclusion</title>
      <p>The integration of ChatGPT into Recommender Systems (RSs) has garnered significant attention,
leading to the exploration of various methods for incorporating these models into RS pipelines.
This study evaluates the performance of ChatGPT-3.5 and ChatGPT-4 as RSs and re-rankers
using a Role-Prompting strategy across three domains: Books, Music, and Movies.</p>
      <p>Our experiments demonstrate ChatGPT’s ability to efectively re-rank recommendation lists.
Utilizing the nDCG metric, we observe improvements in recommendation performance after
re-ranking the lists with ChatGPT, indicating its efectiveness in enhancing the relevance of
recommended items.</p>
      <p>We also analyze the similarity between the recommendation lists generated by ChatGPT
models and those produced by content-based and collaborative filtering RSs. Our findings reveal that
ChatGPT models exhibit a higher degree of similarity to collaborative filtering recommendation
lists, suggesting that these models can leverage latent collaborative information.</p>
      <p>The outcomes of this study suggest that valuable information for recommendation tasks exists
within the latent space of these language models. Future research will focus on designing RSs
that efectively harness this latent collaborative information to improve overall recommendation
performance.</p>
      <p>These results open new avenues for future research. We plan to further explore the latent
collaborative space within these models to enhance recommendation accuracy. Additionally,
we aim to understand the underlying reasons behind ChatGPT’s strong re-ranking capabilities
and investigate content-based recommendation aspects. Ethical considerations regarding user
data collection for training these powerful models also warrant further investigation.</p>
      <p>In conclusion, this study highlights the potential of large language models like ChatGPT
for Recommender Systems. Their deep integration and evolution to produce personalized
recommendations hold significant promise for the future of the field.</p>
      <p>Acknowledgements. The authors acknowledge partial support of the following projects: OVS:
Fashion Retail Reloaded, Lutech Digitale 4.0, Secure Safe Apulia, Patti Territoriali WP1, BIO-D,
and MOST - Centro Nazionale per la Mobilità Sostenibile. We also gratefully acknowledge the
CINECA award under the ISCRA initiative, for the availability of high performance computing
resources and support.</p>
      <p>Additionally, this work has been carried out while Giovanni Servedio was enrolled in the
Italian National Doctorate on Artificial Intelligence run by Sapienza University of Rome in
collaboration with Politecnico Di Bari.
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