News

2023
- March: I am the web chair of CIDR 2024.
- Feb: I gave two talks at FOSDEM 2023:
  - Graph Systems and Algorithms devroom (Graph Systems and Algorithms developer room), co-presented with David Püroja
  - The LDBC benchmark suite (HPC developer room), 10-minute lightning talk
- Jan: David Püroja defended his MSc thesis on the LDBC SNB Interactive v2 workload.
- Jan: I served as a local arrangement chair of CIDR 2023.
- Jan: Our paper DuckPGQ: Efficient Property Graph Queries in an analytical RDBMS was presented at CIDR.
2022
- Dec: Our paper The LDBC Social Network Benchmark: Business Intelligence Workload appeared at PVLDB.
- Nov: TigerGraph and AMD conducted the first successful audit of the LDBC SNB BI workoad.
- Sep–Nov: I was a teaching assistant of the Large-Scale Data Engineering course at VU Amsterdam.
- Aug: Danïel ten Wolde defended his MSc thesis on adding SQL/PGQ in DuckDB and decided to pursue a PhD in our group!
- Jun: I organized the 15th LDBC Technical User Community meeting co-located with SIGMOD 2022 in Philadelphia. I was the session chair of SIGMOD’s “Benchmarking and Performance Expriments” research session.
- May: I was the local chair for the (remote) GrAPL 2022 workshop and acted as session chair.
- Apr: I was a reviewer for GRADES-NDA 2022.
- Jan: I was the Zoom chair of the CIDR 2022 conference and co-authored an experience report on running a hybrid conference.
- Jan: I was a reviewer for TheWebConf 2022’s industry track.
2021
- Sep–Nov: I was a teaching assistant of the Large-Scale Data Engineering course at VU Amsterdam.
- Oct: I appeared on the Code for Thought podcast with Benjamin Steer.
- Sep: Our paper A cross-technology benchmark for incremental graph queries was accepted at the Software and Systems Modeling journal.
- Aug: I organized the 14th LDBC TUC meeting co-located with VLDB 2021.
- Apr: Our paper LSQB: A Large-Scale Subgraph Query Benchmark was accepted at GRADES-NDA 2021. The microbenchmark described in this paper was adopted by a number of GDBMS vendors as a performance regression test.
- Mar–Apr: I was a program committee member of the MEDI 2021 conference and the GRADES-NDA 2021 workshop.
- Jan–Mar: I served as an external reviewer for VLDB 2021.
- Feb: I was a program committee member of the EDBT 2021 conference.
- Jan: I served as the local arrangements chair of the online CIDR 2021 conference.
2020
- Dec: I co-authored a preprint documenting our lessons learnt during the implementation of the SIGMOD 2014 Programming Contest.
- Sep: I presented our paper A GraphBLAS solution to the SIGMOD 2014 Programming Contest using multi-source BFS at HPEC 2020. Slide deck
- Sep: I translated the 1931 seminal paper Graphs and Matrices by Dénes Kőnig from Hungarian to English.
- Aug: I became a steering committee member of the Linked Data Benchmark Council.
- Aug: Our paper Towards Testing ACID Compliance in the LDBC Social Network Benchmark was accepted at TPCTC 2020.
- Aug: I started working at the Database Architectures group of CWI under the supervision of Peter Boncz.
- Jul: LDBC conducted its first successful audit for a new database management system (previous audits targeted systems by vendors within the original LDBC European Union project). I supported the implementation process and supervised the audit.
- Jun: I presented our paper Supporting Dynamic Graphs and Temporal Entity Deletions in the LDBC Social Network Benchmark’s Data Generator at the GRADES-NDA 2021 workshop of SIGMOD.
- Mar: Our paper An incremental GraphBLAS solution for the 2018 TTC Social Media case study was accepted at the GrAPL 2020 workshop of IPDPS.
- Feb: I visited CWI in Amsterdam with Benjamin Steer and Jack Waudby. We worked with Peter Boncz on the LDBC Social Network Benchmark.
- Feb: I gave a talk at FOSDEM’s High-Performance Computing developer room about GraphBLAS.
- Jan: I was a program committee member of the EDBT 2020 conference.
- Jan: Dominik Tomaszuk visited me at BME. We worked on surveying existing graph data models and schema languages.
2019
- Dec: I participated in the Dagstuhl seminar on Big Graph Processing Systems.

Notes

E-bike rental options in Amsterdam

Recently, I had a few family members visiting me in Amsterdam and I wanted to show them around the Dutch countryside. To give us a larger radius – and put towns like Marken, Zaandam, and Naarden comfortably within reach – I decided to rent e-bikes. In this post, I document my findings about the available options and the bikes I rented. Note that my lessons learnt are valid as of summer 2022 and are likely to change in the future....

Self-joins

Introduction A self-join is a relational join operation which joins a table to itself, typically based on equivalence predicates. For example, given the table \(\mathsf{knows}(\mathsf{person1\_id}, \mathsf{person2\_id})\), representing a social graph where people know each other, and aliases of this table \(\mathsf{knows1}, \mathsf{knows2}, \ldots\), take the following query: SELECT knows1.person1_id AS pA, knows1.person2_id AS pB, knows2.person2_id AS pC FROM knows knows1 JOIN knows knows2 ON knows2.person1_id = knows1.person2_id; The query specifies a self-join on the \(\mathsf{knows}\) table, \(\mathsf{knows1} \bowtie \mathsf{knows2}\), and produces two-hop paths in the social graph....

Graph query languages

The maze of graph query languages can be difficult as there are a number of similarly named languages with subtle differences. This document contains a very brief description of popular graph query languages. Languages Property graphs A number of languages exist for defining graph queries over property graphs. Here’s a list of 10 popular languages: Cypher: The declarative graph query language used by the Neo4j graph database. Cypher popularized the ASCII art syntax for defining graph patterns....

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