Publishing, Versioning and Persistence

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Some rules for publishing a resource online:

  • The current version of the resource must always be available at the same URL, unless it moves (send a "301 Moved Permanently" response to redirect to the new URL) or is deleted (send a "410 Gone" response).
  • If the document is updated, a new version of the resource must be created. Each existing version of the resource must remain available at a unique URL.
  • Each version of the resource must link to the previous, next and current versions of the resource.

Accomplishing this should be simple:

  1. Assign a unique file name to each version of the resource.
  2. Create a symlink with a file name that represents the "current" version of the resource, pointing to the appropriate file for the current version.
  3. When a new version of the resource is created, add a "previous version" link from the new version, and update the "next version" link from the previous version.
  4. When a version of the resource is deleted, leave the file as a tombstone, set a property to mark that this version has been deleted, and remove any other properties that should be deleted. Update the next/previous version links in nearby versions, and update the "current version" symlink, if needed.
  5. To change the "current" version, e.g. to roll back to a previous version, simply change the "current version" symlink to point to that version.

This example uses files in a file system, but would work equally well with objects in a database. It's quite similar to how Freebase and Git (and presumably any system which allows any specific version of a resource to be checked out as the "current" version) work, except perhaps for a separate index to handle the relationships between different versions.

I had a go at implementing this in PHP recently, but it's definitely still a work in progress…