Creating / editing UML diagrams

Dear list,

This might be a naïve question...

I'd like to edit the DCAT-AP UML diagram (
https://github.com/SEMICeu/DCAT-AP/blob/master/releases/2.1.0/dcat-ap_2.1.0.png).
Given they have an eap file in their repo, it looks like they used Sparx to
originally create their diagrams. Is there an open source alternative?
Otherwise, they also have SVG, and various other standard LOD file types,
if there's software which can create UML from any of these?

Best,
Chris