I spent a very grateful time in science and education at COMSYS, RWTH Aachen with Prof. Dr.-Ing. Klaus Wehrle (Klaus), and the Computer Networks Group at Brandenburg University of Technology (BTU) with Prof. Dr. rer.-nat. Oliver Hohlfeld, and all gathered family along . I have now come back to ALDI joining the International Data & Analytics subdivision #teamaldi .


  • Empowering Retail
  • Networking & Core Internet, Online Platforms
  • Big Data, Azure, Hadoop, ClickHouse Smiling Face with Hearts
  • import pyspark, ray, numpy, pandas, matplotlib, seaborn, scipy, sklearn, networkx, nltk, gensim, nlp, torch, transformers
  • Empirical Analysis & Visualization, Modeling
  • (Explainable) AI, Machine + Deep Learning
  • Information Embedding, Geometric Deep Learning, (Deep) Graph Learning, Recommender Systems, Natural Language Processing, Forecasting & Anomaly Detection



  • Secure Scaling Infrastructure
  • Data Engineering · Visualization
  • Analysis · Modeling
  • Deep Learning · Artificial Intelligence
  • Project Management · Acquisition
  • Efficient Knowledge Transfer
  • Supervision
  • Solutions
  • Suitcase · Commitment

Latest News

2023-03MiscToday, I successfully defended my final Dr. rer. nat. thesis about anonymous hyperlocal online platforms. Many thanks to my examiners and also to all participants in-person as well as remote. It has been an exciting journey through academia I do not want to miss; thanks to all the great people along the way - is has been an honor for me! You may find the slides here.
2023-01ServiceI am happy to serve in this year’s Program Committee of the LocWeb Workshop once again taking place in conjunction with WWW'23.
2022-11ServiceI am delighted to announce participating in the Technical Program Committee of the ACM Web Science Conference ‘23.
2022-10TeachingWe have been acknowledged as Runner-Up by BTU for our outstanding teaching efforts within both: Our Internet & Measurements lectures - Teaching Day.

Latest Publications ·

Reviewing War: Unconventional User Reviews as a Side Channel to Circumvent Information Controls · arXiv 2023


 José Miguel Moreno,  Sergio Pastrana,  Jens Helge Reelfs,  Pelayo Vallina,  Andriy Panchenko,  Georgios Smaragdakis,  Oliver Hohlfeld,  Narseo Vallina-Rodriguez,  Juan Tapiador


During the first days of the 2022 Russian invasion of Ukraine, Russia’s media regulator blocked access to many global social media platforms and news sites, including Twitter, Facebook, and the BBC. To bypass the information controls set by Russian authorities, pro-Ukrainian groups explored unconventional ways to reach out to the Russian population, such as posting war-related content in the user reviews of Russian business available on Google Maps or Tripadvisor. This paper provides a first analysis of this new phenomenon by analyzing the creative strategies to avoid state censorship. Specifically, we analyze reviews posted on these platforms from the beginning of the conflict to September 2022. We measure the channeling of war messages through user reviews in Tripadvisor and Google Maps, as well as in VK, a popular Russian social network. Our analysis of the content posted on these services reveals that users leveraged these platforms to seek and exchange humanitarian and travel advice, but also to disseminate disinformation and polarized messages. Finally, we analyze the response of platforms in terms of content moderation and their impact.

Content & User Behavior in Anonymous Hyperlocal Online Platforms · Dr. rer. nat. Thesis 2023

BTU - Dr. rer. nat. Thesis 2023

 Jens Helge Reelfs

PDF DOI slides

Nowadays day-to-day digital communication and social life has only fortified with the ongoing pandemic. People enjoy communication and information across various (direct) messaging platforms and accepted its ever-increasing impact on public discourse, and thus society. While most traditional platforms implement user profiles enabling social credit, the new landscape now also includes anonymity. Yet, a new type of applications combining anonymity with a strong spatial focus, hyperlocality, emerged over recent years. To this point, platform implications of both uniquely combined design properties largely remain unknown. In this thesis (with minor exceptions) we provide a first data-driven holistic view on Jodel that combines both properties. We leverage unbiased and complete ground truth information to dissect a plethora of communities across two different countries: Germany & the Kingdom of Saudi Arabia. This work follows a platform perspective identifying four major essentially important areas revolving around the individual. That is, we begin with a broad analysis of three User Adoption processes along three different applications. After discussing our measurements of the start and user base adoption of the German COVID-19 digital contact tracing application, we provide evidence of well-established platforms being re-purposed as a side channel to evade censorship in the ongoing Russo-Ukrainian hybrid war. We further showcase that even the very same platform ingredients may yield vastly different outcomes on the messaging app Jodel. While any online platform builds upon user User Interactions, we structurally characterize Jodel behavior across both countries. We discuss structural disparities and detail platform implications - solely induced by local user behavior. An in-depth look into the Saudi community landscape closes a research gap to platform usage in non-Western societies, identifying fundamental differences. Further, we discuss User Content analyzing information diffusion. Taking content to the next level, we developed a multidimensional classification scheme for intents (why) and topics (what) of social media messages and provide details of a crowdsourced campaign for Saudi Arabian contents. With neural word embeddings as a tool for making text tangible and the prevalence of emoji in social media communication, we discuss quantitative & qualitative insights to word-emoji embeddings reflecting semantics. Additionally, we make such embeddings interpretable and provide evidence that our method is well in line with human judgement. In terms of User Management, we detail insights to distributed moderation processes and model the threat of abusive content. In the long term, platforms need to establish a sustainable, preferably growing, environment. That is, we next discuss user lifetime and possibly early churn factors, while modeling user lifetime from metadata. We finish with a blueprint of data-driven long term quality of experience analyzes in a controlled massively multiplayer online game (MMOG) environment.

Data-Driven Study of Long-Term Gaming Experience · QoMEX 2022

International Conference on Quality of Multimedia Experience 2022

 Jens Helge Reelfs,  Oliver Hohlfeld

PDF Poster DOI data

A subset of massively multiplayer online games (MMOG) feature long-term game rounds in which players interact for months or even years. The player experience of such long-term games cannot be entirely captured by current study methods, in particular not at scale assessing large player populations. To address this challenge, we posit that long-term, round based games such as Tribal Wars (browser-based) enable a data-driven perspective on long-term game dynamics and experience. In a preliminary study, we monitor and characterize the entire longitudinal game state of a Tribal Wars round that was played by 16k players for 1.5 years, enabling us to investigate behavioral patterns of all active players. We identify features that capture the in-game success and relate to the player experience. We show that only successful players keep up playing. We open source our dataset enabling reproducibility & future research.
more ·




Jens Helge Reelfs Photo

Jens Helge Reelfs
Email · helge AT reelfs DOT de
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