Making sense out of data is a matter of perspective.

Digging deeper ever since. Nerd Face


A long journey of adventures - climbing higher and digging deeper ever since. Be greedy.

After finishing my Master's Degree, I decided to conquer the world going into industry. My work at ALDI has taught & given me so much! · Decisions · Is it still fun? - Totally · Is it demanding (enough)? - Yes · Do you still it? - Very much so · Then why leave?

This was not it (yet) · something was calling for more · the next endeavor. Having spent a very grateful time in Science and Education at COMSYS1, Network Architectures Group2, RWTH Aachen, with Prof. Dr.-Ing. Klaus Wehrle (Klaus)1, Prof. Dr. rer.-nat. Oliver Hohlfeld2, and the family,

further following the White Rabbit, I am now a member of the Computer Networks Group at Brandenburg University of Technology (BTU), located in Cottbus, supervised by Oliver.

Decisions once again soon · Yes · Next venture? let's talk

The walk-through get's you to all exciting places.


  • Data, Databases, Big Data
    (data warehousing with ClickHouse)
  • Computing- & Storage Infrastructure
  • import ray, numpy, pandas, matplotlib, seaborn, gensim, scikit-learn, nlp, torch, transformers
  • Online Social Networks
  • Empirical Analysis & Visualization, Modeling
  • (Explainable)AI, Machine + Deep Learning
  • Graph Representations, Information Embedding, Recommender Systems, Natural Language Processing & Generation



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


2021-03PaperFinally, great work with one of my Bachelor students has been successfully presented (paper) at LocWeb'21 WWW'21
2020-12TeachingOn our University’s ‘Tag der Lehre’ (day of teaching), Oliver presented our approach to teach core internet fundamentals using the ETHZ Mini Internet.
2020-08PosterA long night ends… Using Mozilla Hubs, I presented our analysis of web traffic to the official Corona Warn App at SIGCOMM'20.
2020-06PaperToday, I presented our work on Emoji Embeddings (paper) at Emoji'20 ICWSM'20. Thanks for all the cool presented papers!

Latest Publications ·

Understanding & Predicting User Lifetime with Machine Learning in an Anonymous Location-Based Social Network · WWW LocWeb 2021

International Workshop on Location and the Web at WWW 2021

Jens Helge Reelfs, Max Bergmann, Oliver Hohlfeld, Niklas Henckell

PDF arXiv DOI slides

In this work, we predict the user lifetime within the anonymous and location-based social network Jodel in the Kingdom of Saudi Arabia. Jodel’s location-based nature yields to the establishment of disjoint communities country-wide and enables for the first time the study of user lifetime in the case of a large set of disjoint communities. A user’s lifetime is an important measurement for evaluating and steering customer bases as it can be leveraged to predict churn and possibly apply suitable methods to circumvent potential user losses. We train and test off the shelf machine learning techniques with 5-fold crossvalidation to predict user lifetime as a regression and classification problem; identifying the Random Forest to provide very strong results. Discussing model complexity and quality tradeoffs, we also dive deep into a time-dependent feature subset analysis, which does not work very well; Easing up the classification problem into a binary decision (lifetime longer than timespan 𝑥) enables a practical lifetime predictor with very good performance.We identify implicit similarities across community models according to strong correlations in feature importance. A single countrywide model generalizes the problem and works equally well for any tested community; the overall model internally works similar to others also indicated by its feature importances.

Word-Emoji embeddings from large scale messaging data reflect real world semantic associations of expressive icons · ICWSM Emoji 2020

ICWSM Workshop on Emoji Understanding and Applications in Social Media 2020

Jens Helge Reelfs, Oliver Hohlfeld, Markus Strohmaier, Niklas Henckell

PDF arXiv DOI slides data

We train word-emoji embeddings on large scale messaging data obtained from the Jodel online social network. Our data set contains more than 40 million sentences, of which 11 million sentences are annotated with a subset of the Unicode 13.0 standard Emoji list. We explore semantic emoji associations contained in this embedding by analyzing associations between emojis, between emojis and text, and between text and emojis. Our investigations demonstrate anecdotally that word-emoji embeddings trained on large scale messaging data can reflect real-world semantic associations. To enable further research we release the Jodel Emoji Embedding Dataset (JEED1488) containing 1488 emojis and their embeddings along 300 dimensions.

Corona-Warn-App: Tracing the Start of the Official COVID-19 Exposure Notification App for Germany · SIGCOMM Poster 2020

ACM Special Interest Group on Data Communication - Poster 2020

Jens Helge Reelfs, Oliver Hohlfeld, Ingmar Poese

PDF arXiv

On June 16, 2020, Germany launched an open-source smartphone contact tracing app (“Corona-Warn-App”) to help tracing SARSCoV- 2 (coronavirus) infection chains. It uses a decentralized, privacy preserving design based on the Exposure Notification APIs in which a centralized server is only used to distribute a list of keys of SARSCoV-2 infected users that is fetched by the app once per day. Its success, however, depends on its adoption. In this poster, we characterize the early adoption of the app using Netflow traces captured directly at its hosting infrastructure. We show that the app generated traffic from allover Germany—already on the first day. We further observe that local COVID-19 outbreaks do not result in noticeable traffic increases.
more ·




Jens Helge Reelfs Photo

Helge Reelfs
Brandenburg University of Technology
Chair of Computer Networks
Konrad-Wachsmann-Allee 5
03046 Cottbus, Germany
Email ·
My Group
Chair of Computer Networks
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