VLDB 2026 Research / reviewers in the wild / expert
Patricia Callejo
dblp:190/1431 · also Patricia Callejo-Pinardo
· DBLP profile ↗
13ranked-venue papers
5as first author
9since 2021 · last 2025
0000-0001-6124-6213ORCID · verified
Domains — the database's venue-derived domains; a paper can count in several
Computer networks · 6 · 5 first-author · 3 since 2021Applied, interdisciplinary, general and emerging computing · 5 · 4 since 2021Human-computer interaction and ubiquitous computing · 3 · 3 since 2021Databases, data management, data science and information retrieval · 2 · 1 since 2021Systems, architecture and hardware · 1 · 1 since 2021Security and privacy · 1 · 1 since 2021
| Year | Publication | Venue | Position |
|---|---|---|---|
| 2025 | Analyzing Student Use of Spacing and Interleaving Strategies in Interactions with GenAI-Powered Chatbots in Programming Courses
Rodrigo Prestes Machado, Carlos Alario-Hoyos, Patricia Callejo, Iria Estévez-Ayres, Carlos Delgado Kloos |
CSEDU (2) | 3 |
| 2025 | How Challenges Become Opportunities: Micro-credentials and Artificial IntelligenceabstractAs we move from the Information Age to the Intelligence Age, universities must redefine themselves taking into account recent challenges. Two of these challenges are Micro-credentials and Artificial Intelligence (AI). Micro-credentials certify the learning outcomes of short-term learning experiences, which are typically more flexible and tailored to specific, job-relevant skills, meeting the increasing demand for continuous education. These learning experiences are normally referred to as micro-credential courses or micro-credential programs and disrupt traditional degree models. On the other hand, Artificial Intelligence is disrupting every single aspect of our life and work. Artificial Intelligence tools can work as assistants helping in all kinds of tasks that were previously reserved for humans. Artificial Intelligence can be used in education in many ways, such as to create personalized learning paths, create and optimize educational multimedia content such as text, voice, image, or video, tutor students, and monitor student progress in real-time, contributing to the acquisition of learning outcomes. Putting the two challenges together, Artificial Intelligence can also contribute to generate micro-credentials by ensuring learners demonstrate competence in practical, job-specific skills, enhancing their credibility for employers. Therefore, Artificial Intelligence can playa pivotal role in advancing micro-credential courses and programs, helping universities redefine their offerings to provide personalized, adaptable, and industry-relevant learning experiences. Artificial Intelligence can help in designing the content and the learning experience as with courses in general, but it can also help in designing the specificities of micro-credential courses. The specific “skills” provided by Artificial Intelligence for defining micro-credentials range from clerical work related to mastering formats such as ELM or OpenBadges that are needed to construct digital credentials to creative sug-gestions that aid in designing the details of the micro-credential course. Alternatively, the micro-credentials designed can include topics about Artificial Intelligence, helping the workforce on this important area. This paper analyzes the interplay of these two challenges and how they can help each other, making opportunities out of challenges. Carlos Delgado Kloos, Carlos Alario-Hoyos, Rebiha Kemcha, Pedro Manuel Moreno-Marcos, Iria Estévez-Ayres, Patricia Callejo, Pedro J. Muñoz Merino, María-Blanca Ibáñez-Espiga, Mario Muñoz Organero |
EDUCON | 6 |
| 2025 | Big Help or Big Brother? Auditing Tracking, Profiling, and Personalization in Generative AI Assistants
Yash Vekaria, Aurelio Loris Canino, Jonathan Levitsky, Alex Ciechonski, Patricia Callejo, Anna Maria Mandalari, Zubair Shafiq |
USENIX Security Symposium | 5 |
| 2025 | Unveiling Network Performance in the Wild: An Ad-Driven Analysis of Mobile Download SpeedsabstractAccurate measurement of mobile network performance is crucial for optimizing user experience and ensuring regulatory compliance. Traditional methods like crowdsourcing approaches, though effective, depend heavily on user participation and extensive infrastructure. In this paper, we introduce adNPM, a novel technique for measuring download speed by embedded measurement code in ads displayed across web browsers and mobile apps, without requiring user participation. Through controlled lab tests and real-world deployments in 15 countries, we demonstrate that adNPM achieves accuracy comparable to well-established tools like Speedtest by Ookla and Opensignal while significantly reducing data consumption. Miguel A. Bermejo-Agueda, Patricia Callejo, Rubén Cuevas Rumín, Ángel Cuevas, Ramakrishnan Durairajan, Reza Rejaie, Álvaro Mayol |
WWW | 2 |
| 2024 | How can Generative AI Support Education?abstractThe possible applications of GenAI (Generative AI) in education alone are so manyfold and overwhelming that it is useful to have an overview of the many possibilities that are opening up. In this paper, we try to organize some of the low-hanging fruits that can help instructors, learners, and educational managers use GenAI applications to improve educational performance. For instructors, GenAI can help in gaining a deeper understanding of the topics to be taught, preparing educational materials, and facilitating the enactment phase in class. Learners can be assisted in getting personalized content and feedback, having GenAI as a participant in forums, or for self-reflection and emotions detection. Managers and other stakeholders can profit from Academic Analytics, bias detection, course repurposing, and many other uses. In this paper, we also present a use case detailing some initial actions we are implementing for a Programming with Java course. One action is to explicitly identify, in each problem set, the competencies being developed. Another one is the development of a chatbot, fine-tuned with the course material, which can be used by students as a tutor. The third action is to use a GenAI tool to generate questions aimed at assessing whether students truly grasp the programming project they have supposedly developed. AI is here to stay, in spite of the issues it opens up, and therefore it is never too early to start experimenting with it in practice. Carlos Delgado Kloos, Carlos Alario-Hoyos, Iria Estévez-Ayres, Patricia Callejo, M. Á. Hombrados-Herrera, Pedro J. Muñoz Merino, Pedro Manuel Moreno-Marcos, Mario Muñoz Organero, María-Blanca Ibáñez-Espiga |
EDUCON | 4 |
| 2024 | Watching TV with the Second-Party: A First Look at Automatic Content Recognition Tracking in Smart TVsabstractSmart TVs implement a unique tracking approach called Automatic Content Recognition (ACR) to profile viewing activity of their users. ACR is a Shazam-like technology that works by periodically capturing the content displayed on a TV's screen and matching it against a content library to detect what content is being displayed at any given point in time. While prior research has investigated third-party tracking in the smart TV ecosystem, it has not looked into second-party ACR tracking that is directly conducted by the smart TV platform. In this work, we conduct a black-box audit of ACR network traffic between ACR clients on the smart TV and ACR servers. We use our auditing approach to systematically investigate whether (1) ACR tracking is agnostic to how a user watches TV (e.g., linear vs. streaming vs. HDMI), (2) privacy controls offered by smart TVs have an impact on ACR tracking, and (3) there are any differences in ACR tracking between the UK and the US. We perform a series of experiments on two major smart TV platforms: Samsung and LG. Our results show that ACR works even when the smart TV is used as a ''dumb'' external display, opting-out stops network traffic to ACR servers, and there are differences in how ACR works across the UK and the US. Gianluca Anselmi, Yash Vekaria, Alexander D'Souza, Patricia Callejo, Anna Maria Mandalari, Zubair Shafiq |
IMC | 4 |
| 2023 | A Deep Dive into the Accuracy of IP Geolocation Databases and its Impact on Online AdvertisingabstractThe quest for every time more personalized Internet experience relies on the enriched contextual information about each user. Online advertising also follows this approach. Among the context information that advertising stakeholders leverage, location information is certainly one of them. However, when this information is not directly available from the end users, advertising stakeholders infer it using geolocation databases, matching IP addresses to a position on earth. The accuracy of this approach has often been questioned in the past: however, the reality check on an advertising stakeholder shows that this technique accounts for a large fraction of the served advertisements. In this paper, we revisit the work in the field, that is mostly from almost one decade ago, through the lenses of big data. More specifically, we, i) benchmark two commercial Internet geolocation databases, evaluate the quality of their information using a ground-truth database of user positions containing over 2 billion samples, ii) analyze the internals of these databases, devising a theoretical upper bound for the quality of the Internet geolocation approach, and iii) we run an empirical study that unveils the monetary impact of this technology by considering the costs associated with a real-world ad impressions dataset. Patricia Callejo, Marco Gramaglia, Rubén Cuevas Rumín, Ángel Cuevas |
IEEE Trans. Mob. Comput. | 1 |
| 2023 | CarbonTag: A Browser-Based Method for Approximating Energy Consumption of Online AdsabstractEnergy is today the most critical environmental challenge. The amount of carbon emissions contributing to climate change is significantly influenced by both the production and consumption of energy. Measuring and reducing the energy consumption of services is a crucial step toward reducing adverse environmental effects caused by carbon emissions. Millions of websites rely on online advertisements to generate revenue, with most websites earning most or all of their revenues from ads. As a result, hundreds of billions of online ads are delivered daily to internet users to be rendered in their browsers. Both the delivery and rendering of each ad consume energy. This study investigates how much energy online ads use in the rendering process and offers a way for predicting it as part of rendering the ad. To the best of the authors’ knowledge, this is the first study to calculate the energy usage of single advertisements in the rendering process. Our research further introduces different levels of consumption by which online ads can be classified based on energy efficiency. This classification will allow advertisers to add energy efficiency metrics and optimize campaigns towards consuming less possible. José González Cabañas, Patricia Callejo, Rubén Cuevas Rumín, Steffen Svartberg, Tommy Torjesen, Ángel Cuevas, Antonio Pastor 0002, Mikko Kotila |
IEEE Trans. Sustain. Comput. | 2 |
| 2022 | Measuring DoH with web adsabstractIn this paper we present a large measurement study of the impact on the performance of the adoption of HTTPS as a transport for the DNS protocol (DoH) with public resolvers compared to the existent approach of using non-encrypted transport of DNS queries with the resolver services locally provided by ISPs. Using on web-ads as the mean to execute our tests, we perform over 42 million measurements from more than 4 million vantage points distributed in 32 countries and served by over 2,500 ISPs. We find that, the median resolution time increased 17 ms when using DoH with Cloudflare, 41 ms when using DoH with Quad9, 68 ms when using DoH with Google and 170 ms when using DoH with DNS.SB, compared to using Do53 with the local resolver for a non-cached name. We find similar increases even when using caching. The results presented in the paper contribute to the ongoing discussion of the tradeoffs involved in the combined adoption of public resolvers and DoH. Patricia Callejo, Marcelo Bagnulo, Jaime González Ruiz, Andra Lutu, Alberto García-Martínez, Rubén Cuevas Rumín |
Comput. Networks | 1 |
| 2019 | Q-Tag: a transparent solution to measure ads viewability rate in online advertising campaignsabstractViewability is one of the most important metrics used in ad-tech to measure the performance quality of ad campaigns. The viewability standard defines the visibility conditions an ad impression must meet to achieve a sufficient marketing effect to be considered viewed. The ad-tech industry offers opaque measures of viewability whose performance is questionable. To address this issue, we propose a novel methodology for measuring viewability in ad campaigns. The disclosure of the functional details of this technique makes it reproducible and auditable. Our solution has been deployed in production by a Demand Side Platform (DSP) to measure the viewability rate of the ad campaigns. Leveraging the infrastructure of this DSP, we compare the performance of our methodology with a commercial solution. Both techniques report a similar overall viewability rate of 50%. However, our solution measured the viewability in 93% of the ads served by the DSP, unlike to 74% of the ads measured by the commercial solution. A rough estimation indicates that this increase in the measured rate may lead to a revenue increase of $3.5 million per year for a mid-sized DSP serving 100M of ads per day. Patricia Callejo, Antonio Pastor 0002, Rubén Cuevas Rumín, Ángel Cuevas |
CoNEXT | 1 |
| 2019 | Nameles: An intelligent system for Real-Time Filtering of Invalid Ad TrafficabstractInvalid ad traffic is an inherent problem of programmatic advertising that has not been properly addressed so far. Traditionally, it has been considered that invalid ad traffic only harms the interests of advertisers, which pay for the cost of invalid ad impressions while other industry stakeholders earn revenue through commissions regardless of the quality of the impression. Our first contribution consists of providing evidence that shows how the Demand Side Platforms (DSPs), one of the most important intermediaries in the programmatic advertising supply chain, may be suffering from economic losses due to invalid ad traffic. Addressing the problem of invalid traffic at DSPs requires a highly scalable solution that can identify invalid traffic in real time at the individual bid request level. The second and main contribution is the design and implementation of a solution for the invalid traffic problem, a system that can be seamlessly integrated into the current programmatic ecosystem by the DSPs. Our system has been released under an open source license, becoming the first auditable solution for invalid ad traffic detection. The intrinsic transparency of our solution along with the good results obtained in industrial trials have led the World Federation of Advertisers to endorse it. Antonio Pastor 0002, Matti Antero Parssinen, Patricia Callejo, Pelayo Vallina, Rubén Cuevas Rumín, Ángel Cuevas, Mikko Kotila, Arturo Azcorra |
WWW | 3 |
| 2017 | Opportunities and Challenges of Ad-based Measurements from the Edge of the NetworkabstractFor many years, the research community, practitioners, and regulators have used myriad methods and tools to understand the complex structure and behavior of ISPs from the edge of the network. Unfortunately, the nature of these techniques forces the researcher to find a balance between ISP-coverage, user scale, and accuracy. In this paper we present AdTag, a network measurement paradigm that leverages the opportunistic nature of online targeted advertising to measure the Internet from the edge of the network. We discuss and formalize AdTag's design space---including technical, ethical, deployability and economic factors---and its potential to analyze a wide spectrum of Internet connectivity aspects from the browser. We run several experiments to demonstrate that AdTag can be tailored towards geographic and device-based user groups, finding also several challenges to be faced in order to maximize the number of samples. In a 7-day campaign, AdTag could access more than 20K ISPs at a global scale (185 countries) using millions of edge nodes. Patricia Callejo, Conor Kelton, Narseo Vallina-Rodriguez, Rubén Cuevas Rumín, Oliver Gasser, Christian Kreibich, Florian Wohlfart, Ángel Cuevas |
HotNets | 1 |
| 2016 | Independent Auditing of Online Display Advertising CampaignsabstractThe reported lack of transparency of the online advertising market may seriously affect the interests of advertisers. In this paper, we present a novel methodology that allows advertisers to independently assess the quality of display advertising campaigns. This methodology also serves to audit the accuracy and completeness of reports delivered by the vendor responsible for running a campaign. We have applied our methodology in 8 display ad campaigns configured in Google AdWords, which overall produced 160K ad impressions displayed in more than 7K publishers. Our results reveal that AdWords seems to provide incomplete information to advertisers. Specifically, we found that: (i) AdWords did not report 57% of publishers where ad impressions from our campaigns were delivered, (ii) AdWords reports a large fraction of contextually meaningful impressions based on (non-disclosed) criteria different from the publisher’s theme, (iii) higher CPM investment does not lead to get impressions delivered to more popular publishers, (iv) AdWords does not offer default control of frequency cap, (v) around 10% ad impressions in two of our campaigns were delivered to IP’s from Data Centers. The industry considers these IPs to be likely related to fraud. These findings should contribute to open a debate between advertisers and Ad Tech vendors to standardize the utilization of independent auditing methodologies as the one presented in this work. Patricia Callejo, Rubén Cuevas Rumín, Ángel Cuevas, Mikko Kotila |
HotNets | 1 |