The Eclipse Layout Kernel

TL;DR

The paper presents the Eclipse Layout Kernel, an open-source graph drawing library supporting complex layouts and ports, highlighting its history, key algorithms, architecture, and practical applications over fifteen years.

Contribution

It provides a comprehensive overview of ELK's development, key algorithms, architecture, and lessons learned, emphasizing its impact on research and practical graph layout solutions.

Findings

ELK supports complex graph layouts with ports and compound structures.

ELK has been adopted in numerous academic and commercial projects.

The paper discusses lessons learned and future threats to open-source graph drawing tools.

Abstract

The Eclipse Layout Kernel (ELK) is a collection of graph drawing algorithms that supports compound graph layout and ports as explicit anchor points of edges. It is available as open-source library under an EPL license. Since its beginning, ELK has served both as a research vehicle for graph drawing algorithms, and as a practical tool for solving real-world problems. ELK and its transpiled JavaScript cousin elkjs are now included in numerous academic and commercial projects. Most of the algorithms realized in ELK are described in a series of publications. In this paper, the technical description concentrates on the key features of the flag-ship algorithm ELK Layered, the algorithm architecture, and usage. However, the main purpose of this paper is to give the broader view that is typically left unpublished. Specifically, we review its history, give a brief overview of technical papers, discuss lessons learned over the past fifteen years, and present example usages. Finally, we reflect on potential threats to open-source graph drawing libraries.