Complex sentence: Referring to an online document by its DOI provides more stable linking than simply using its URL, because if its URL changes, the publisher only needs to update the metadata for the DOI to link to the new URL.
Split into simpler sentences: Referring to an online document by its DOI shall provide a more stable linking than simply using its URL. Everytime a URL changes, the publisher has to update the metadata for the DOI to link to the new URL.