|Figure 1: Web Archive Weather Underground Example Showing the Different Ages of Embedded Resources|
The Web Archive, as a service external to the resource that it is trying to preserve, only has access to resources that exist at the time it can make a crawl, leading to inconsistencies. Wikis, on the other hand, have access to all resources under their control, embedded or otherwise.
This is why it is surprising that MediaWiki, even though it allows for access to all previous revisions of a given page, does not tie the datetime of those embedded resources back to that main page.
A pertinent example is that of the Wikipedia article Same-sex marriage law in the United States by state.
|Figure 2: Screenshot of Wikipedia article on Same-sex marriage law in the United States by state|
|Figure 3: Screenshot of the same Wikipedia page, but for a revision from June of 2013|
|Figure 4: The June 2013 revision of the embedded map resource|
|Figure 5: Listing of all of the revisions of the map resource on Wikipedia|
For this particular topic, any historian (or paralegal) attempting to trace the changes in laws on this topic will be confused when presented by a map that does not match the text, and may possibly question the validity of this resource as a whole.
We tried to address this issue with the Memento MediaWiki extension. MediaWiki provides the ImageBeforeProduceHTML hook, which appears to do what we want. It provides a $file argument, giving access the the LocalFile Object for the image. It also provides a $time argument that signifies the Timestamp of file in 'YYYYMMDDHHIISS' string form, or false for current.
We were perplexed when the hook did not perform as expected, so we examined the source of MediaWiki version 1.22.5. Below we see the makeImageLink function that calls the hook on line 569 of Linker.php.
Alternatively, we considered using the &$res argument from that hook to replace the HTML with the images of our choosing, but we would still need to use the object provided by the $file argument, which has no ready-made way to select a specific revision of the embedded resource.
At this point, in spite of having all of the data needed to solve this problem, MediaWiki, and transitively Wikipedia, does not currently support rendering old revisions of articles as they truly looked in the past.
--Shawn M. Jones