# The Emergence of Software Diversity in Maven Central

## TL;DR

This paper investigates how the immutability of Maven Central artifacts and version selection contribute to the emergence and persistence of software diversity among library versions in the repository.

## Contribution

It provides an empirical analysis of version diversity in Maven Central, revealing the extent and patterns of multiple versions being actively used and favored.

## Key findings

- Over 30% of libraries have multiple actively used versions.
- More than 50% of versions are used for popular libraries.
- 17% of libraries have dominant versions significantly more used.

## Abstract

Maven artifacts are immutable: an artifact that is uploaded on Maven Central cannot be removed nor modified. The only way for developers to upgrade their library is to release a new version. Consequently, Maven Central accumulates all the versions of all the libraries that are published there, and applications that declare a dependency towards a library can pick any version. In this work, we hypothesize that the immutability of Maven artifacts and the ability to choose any version naturally support the emergence of software diversity within Maven Central. We analyze 1,487,956 artifacts that represent all the versions of 73,653 libraries. We observe that more than 30% of libraries have multiple versions that are actively used by latest artifacts. In the case of popular libraries, more than 50% of their versions are used. We also observe that more than 17% of libraries have several versions that are significantly more used than the other versions. Our results indicate that the immutability of artifacts in Maven Central does support a sustained level of diversity among versions of libraries in the repository.