I would like to make relative links to pictures in an Inkscape file. So when I move the project files (images and the Inkscape master), I wouldn't have to relink the images.
What is the proper way to do this?
< xlink:href="file:///home/foouser/svg/20150721_210652-0.JPG" --- > xlink:href="20150721_210652-0.JPG"
After saving, closing, and moving your svg file along with your image file, Inkscape should still display the image in your file. Also note that after re-opening, Inkscape will keep the xlink:href attribute, but also maintain a separate attribute called sodipodi:absref that will store the absolute location of the image. I've found that this doesn't matter -- you can still move your files around and Inkscape will refer to the xlink:href attribute to find your image.
Tested on Inkscape 0.48
../stuff/file.ext indeed should work.
For a full guide see here: http://libregraphicsworld.org/blog/entry/inkscape-embedding-or-linking ;-)
If you are not familiar with the XML editor it might be more convenient to just right-click on the figure --> Image Properties --> URL: "../my_relative_path/my_figure.jpg".