8

Is it possible to find tag-info (tag-wiki and tag-excerpt) for the tag which was deleted?

I ask because sometimes it might be useful to see the information in those tag-wikis. For example, some of the information could be added to another tag.

To mention a specific example, a tag named (double-factorial) was created on math.SE. After some discussion it was generally agreed that it is better to have this question tagged (factorial) and remove (double-factorial) tag.

Let's say that someone wants to mention in the tag-excerpt/tag-wiki that this tag is also for questions about double factorials. It seems reasonable to check the tag-wiki of the removed tag. If it had good description of double factorials, it can be (at least partially) copied to the tag-wiki for factorial.

In this particular case I was lucky enough that there was a suggestion for the tag-wiki by low reputation users. So by going through review history I was able to find a review of this suggested edit here and here. From there I was able to find link to revision history for the tag-wiki and tag-excerpt. (I would probably have found it faster by checking the tag-creator activity tab, since the same user created both the tag and tag-wiki.) EDIT: Actually, after Revetahw's answer with the Wayback Machine snapshot was posted, it revealed that there was one more "reincarnation" of the same tag with this tag-wiki and tag-excerpt.

Is there an easier way to find tag-info for deleted tags? Would it be possible to find those links if I did not know who created the tag-wiki and if it wasn't shown among suggested edits?

3

Yes, you can use the Stack Exchange Data Explorer. I've created this query, which'll do what you want:

select e.body, w.body
  from tags t
  left outer join posts e
    on t.excerptpostid = e.id  
  left outer join posts w
    on t.wikipostid = w.id
 where t.tagname = ##tagname:string##

If you click on Text-only results it'll be easier to see the entire Wiki, which is:

Series, integrals, and formulas involving the double factorial. The double factorial is defined as $n!!=n(n-2)(n-4)\cdots(n-2\lfloor n/2\rfloor)$. It is usually applied to odd numbers since $(2n)!!$ can easily be written as $2^nn!$.

For odd numbers, we have $$ (2n-1)!!=\frac{(2n)!}{2^nn!} $$

  • 1
    Just to clarify - this will only return the tag-wiki of a deleted tag if I try the query after deletion but before the update of data in SEDE, right? When I try the query for double-factorial now, it returns no result. – Martin Aug 5 '17 at 4:14
  • @Martin deleted tag wiki's don't make it into SEDE, even the postswithdeleted is empty for posttypes 4 and 5 (excerpt and wiki). I will not test this but IIRC if you recreate the tag, the previous tag-wiki gets re-instantiated. I remember I had seen such report but don't know if that was a fluke, a one-time incident or by-design. It might need unicorns ... – rene Aug 6 '17 at 6:49
  • Possibly @Martin – ben is uǝq backwards Aug 6 '17 at 7:46
  • @rene I don't think that tag-info gets recreated - I have described one instance of this I remember in this question: If a tag is removed and later created again, is the original tag-info recreated, too? (Perhaps we get some kind of official answer in that post.) – Martin Aug 6 '17 at 8:12
3
+50

There is a list of orphaned tag wikis (i.e. tag wikis from now-deleted tags) visible to moderators at /admin/orphan-wikis (or from a link on the mod links page).

Unfortunately the orphaned wiki page isn't very user-friendly; There is no indication of which tag a wiki came from and there is no UI to do anything with the wiki itself. All you get is a list of each wiki's content and a link to the revision history.

There are some existing feature requests to improve the functionality of orphan wikis:

But we have to work with what we have...

So if you can't otherwise find the wiki (e.g. from a suggested edit) then you could ask a moderator to find it for you. The revision for the wiki is still public so a moderator could simply find the relevant wiki and pass you a link to the revision.

3

It's not perfect, but you could use a third party archive, such as the Wayback Machine.

For example, the double-factorial tag info which you mention in OP is stored in The Wayback Machine (although it is a bit of an old snapshot, which is a serious drawback to this method.)

If you want to find any tag (including ones that are now deleted), you can take this URL

http://web.archive.org/web/*/https://math.stackexchange.com/tags/double-factorial/info

Replace math.stackexchange.com with the URL of the site in question and double-factorial with the name of the tag you want to look up.

The obvious drawback to using this method is that the Wayback Machine only fetches data occasionally, and thus you will often not find the latest revision of the tag information. I am sure there are also some tags that have not been fetched at all.

Useful addition by OP:

Another option could be trying http://web.archive.org/web/*/https://math.stackexchange.com/‌​questions/tagged/dou‌​ble-factorial. Assuming the snapshot of that page exists, it shows at least tag-excerpt. (This does not work for the tag in question, but it is probably worth trying.) Similarly, it might be worth trying Google cache, at least if the old tag has been removed only recently.

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    Interestingly enough, the tag-info found in Wayback Machine is completely different from the tag-wiki and tag-excerpt I have found. This suggests that the tag was created and removed more than once. – Martin Aug 12 '17 at 13:29
  • @Martin That is curious. – Revetahw Aug 12 '17 at 13:38

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