To that end, 500+ reputation users may have noticed that I've added some text to the sidebar (under the tip):

Want to help? Consider retagging questions with no arXiv tag.

If you click the link, a red box should appear around any question that doesn't use any arXiv tags (actually, it just checks if any of the tags contains a dot, but non-arXiv tags shouldn't be using dots). Please let me know if this misbehaves in any way or if the functionality can be improved somehow (e.g. highlight the questions some other way, or include a link to this tagging guide). Also, are there other tasks that should be encouraged/facilitated in a similar manner? For example, once we have some 10k+ rep users, we could encourage them to look over questions which are candidates for closing/reopening/deleting (10k is the threshold beyond which you have access to that information).

Gosh, to imagine that my interaction with MO could be useful and important for somebody is a cool idea. Actually, I'd be glad to work in that mode as well.

@Andrew, I think this particular idea will not work, but a trial is fine with me.

But I feel as though I'm losing this one heavily so I'll bow out now while I still have some dignity left!

That's good enough speed for me!

See also this meta.SO post

Why isn't it a good use for tags? Are tags purely for searching by? Aren't they supposed to be so that I can see in the summary view whether or not it's worth looking at the details? In that case, what I really want to see is:

1. General area: am I even going to understand the question, or be able to make a sensible contribution?
2. Urgency: should I look at it now, or come back to it later when I've got more time?

What more do you want to know in the list summary?

How often do people actually search by tag? You could look at the logs and find out: I'd be quite interested to know. Are tags useful for limiting searches to see if a question has been asked before? Do people really search by tags to find interesting questions to ask? How, exactly, are people using tags? How can you help people make the most of tags?

I'm trying to give you my answers to those questions. I don't expect my views to have any more weight than anyone else's, but if I don't tell you what I think then that's not helpful to either of us!

I don't think tags are just about searching. I think that they also give information about the problem. As they are always displayed (in particular, in the list view) then they are a good way to provide context for a problem. So if I see a problem that says "loop group" but then see that it is marked "ag.algebraic-geometry" then I'll probably skip it. Similarly, if I see a complicated problem that says "idle-speculation", again I'll skip it.

As an example from "history", take Ben Webster's question on whether or not there are "scaling up" operations on topological spaces that correspond to "scaling up" of rings. That felt like an "idle-speculation" question so I gave an "idle-speculation" answer. However, knowing whether or not it was idle speculation or crucial-for-thesis would have altered how I answered.

Similarly, Theo has asked some very technical questions in differential topology. I doubt that anyone just knows the answer. I could think about them for a bit and maybe make one or two suggestions as to how to proceed. But exactly how important are they? How useful would it be for me to do that? If they were just idle-speculation, then I won't bother. If they were "crucial for thesis" then I would.

I don't think that a tag would be useful here, as I can't think of why I would ever want search for idle-speculation (although I might want to ignore it.) But I do think it is a good idea for people to give a general idea of how long they have spent thinking about something.

I think it could be useful to summarize possible tagging solutions. Here are the ones that come to my mind, listed in the order of my personal preferences:

1. Algebraic-Geometry
2. algebraic-geometry
3. AG-algebraic-geometry
4. AG.algebraic-geometry
5. math.AG-algebraic-geometry
6. ag.algebraic-geometry
7. ag-algebraic-geometry
8. math.ag-algebraic-geometry

Note that solutions 1, 3, 4, 5 use uppercase letters in the tags which is currently technically impossible, but theres' a meta.SE feature request by Anton about that.

By the way, at least on Meta.SO, it's technically possible to designate top-level tags and require that every post has at least one of these.

I know you want to get it right, but can we have a system that is nearly alright and that is stable for a little while?

Whatever the case on that particular issue, it'd be useful to be able to go through the list of tags and select a whole bunch as "interesting" instead of having to put them in one by one. Is there a way to do this, does anyone know?

(If I don't get satisfactory answers from you lot, I'll go and bug the meta guys on S[OE]. You have been warned.)

I object to math.ag as a tag. It is not intuitive to people who don't already know what it means. Of course, I do know what it means, but there are plenty of areas where I don't. COmplex numbers, ComplexAnalysis or ComplexVariables? Is SEt theory a category, or is that a branch of LOgic? And I plan to use the site to ask plenty of questions outside my fields of expertise.

If we use ag.algebraic-geometry, we should probably have a FAQ like "Why are people using those funny two letter abbreviations?"

I seem to differ from everyone else, but I'll state my ideal solution. I think it would be fine to simply say "Please use at least one broad area tag. A list of standard broad area tags, based on the arXiv classification system, is here." Then "here" would be a link to a static page listing the subject tags. I don't see why we need to make the tags look odd and be harder to remember.

People have mentioned ease of retagging. Can't we just solve this with a boolean search? For example, here are all the questions not tagged with number-theory, representation-theory, algebraic-topology, algebraic-geometry or logic. We could even have a link on the Tips and Tricks page to a search for all questions without arXiv tags, for the benefit of anyone who wants to do retagging.

The conclusion being that perhaps the most important factor in choosing canonical names is how the suggestion algorithm works. The obvious search on meta.stackexchange threw up too many posts for me to bother looking through them all right now, but maybe that's a useful bit of digging someone could do (or perhaps someone already knows it).

Since moderators still can't rename tags (only merge tags), if you see a question at the top of the home page that needs an arXiv tag, or has an old version of the arXiv tag, please retag it. As soon as one instance of the correct tag exists, a moderator can easily convert the rest of them.

First, it seems to be close to consensus that "ag-algebraic-geometry" tags are unpleasant. To summarize what people think about them:

Ben "I'll admit, I'm not impressed."

Andrew Stacey "@Ben: Okay, okay, I surrender ..."

me "the topic deserves a top-level post and some thought going into it"

But anyway, that's done. However, here's my suggestion: once we have the ability for uppercase letters in the tags, rename them to "Algebraic-Geometry" and so on, rather then "AG-algebraic-geometry" (which is redundant).

I'm thinking of

• changing [analysis] to [ca-classical-analysis], leaving [odes] alone,
• changing [k-theory] to [kt-k-theory], leaving [homology] alone,
• changing [ring-theory] to [ra-rings-and-algebras] or [ra-ring-theory] and not having an [algebras] tag.

Opinions?

(Just in case one of them drops by here, I hope this isn't interpreted as me/us trying to "game" the system. If it is, I'll instantly withdraw the suggestion. My intention is purely that I want us to be able to convey how much we like having MO.)

For more on how to tag you question effectively

Edit: @Andrew: I actually made the feature-request before your comment about distributing feature-requests. I think it's fine for anybody to just post bug reports and feature-requests as they come up, without worrying about distributing the list of askers. Of course, it helps if the request is relevant to other SE sites (or can be made relevant to them), but don't worry about that. If other SE users don't think it's important, they won't vote it up. On that note, perhaps we should reserve some bug reports and feature requests for people who don't have enough reputation to vote on meta.SE.

Of the people who frequent meta.MO, here are the ones I know of who are on meta.SE: Scott Morrison, Andrew Stacey, Ilya Nikokoshev, David Brown, and myself. I encourage everybody else to head over there and earn a little rep, since meta.SE votes help get features implemented and bugs fixed.

@Ben: Okay, okay, I surrender ...

On cases, is it possible to make tags case insensitive? Or shall I put that over at meta.SE?

(On that note, whilst I have no wish to "game" the meta.SE system, I think it makes sense to spread the load a little of making feature requests and so forth as it will give the meta.SE people an idea of how popular mathoverflow is compared to other sites. However, I'm hesitant at just heading on over and spouting forth about how much better mathoverflow would be if we just had this or that new feature which is why I would tend to bring them up here first to get a sense of whether or not it's just me or not. Not being at Berkeley, I'm not surrounded by hordes of other MOwers to chat with over tea - the one other NTNU person that I know of who lurks here is on sabbatical Somewhere Else!)

I would imagine it possible that a breakthrough in understanding something happens. For the purposes of the hypothetical example, let it be a fundamental lemma, describable by tags "algebraic-geometry geometric-langlands fundamental-lemma". So, several dozens of people post lots of questions tagged to that extent, e.g. 200 questions.

During that process, each individual question is posted with a knowledge of previous ones. Therefore, at some point somebody is tired of putting all three tags (+somebody following "algebraic-geometry" complains about the proliferation of fundamental-lemma questions) and that person might just decide to post under only "fundamental-lemma", rather then under all tags. Others then shift behavior and start to use the remaining 4 tags to fine-grain their question within a big topic.

Without any guidance about tagging, the discovery process works, roughly speaking, under the rules of the free market, that is, for the question/answer pair to be successful, an interaction between only one poster and one asker is required (the more people involved, the better, but it's still a voluntary exchange between consenting adults). This is not the optimal social equilibrium: some guidance useful to other people is worth giving, so it makes sense to force/nudge people toward putting universally recognizable tags.

But too much nudge, I worry, might kill the abovementioned discovery process, where from the everyday work of dozens of regular people suddenly a new behavior -- the radical change -- arises, in this case in the form of a new top-level tag. With too easily recognizable top tags, of course, everyone would continue to put the same AG-algebraic-geometry on the fundamental-lemma until eternity. Why this could be less than optimal? Just look at "high energy physics - theory" archive.

These comments should be interpreted as just general thoughts, so, sure, I'm fine with retag. Just something to think.

@Ilya: I'd just leave non-arxiv tags alone. As a rule, a question should have an arxiv area tag. Sometimes the question is valid but no arxiv tag fits. That's not a problem, but it shouldn't happen too often. I'm not proposing rigidly enforcing the "must have an arxiv tag" rule, but encouraging it as a social convention and making it easy to retag to maintain that social convention.

I should point out that renaming a tag is a trivial matter for moderators. We don't have to do anything crazy like manually go and change all the tags. This also makes it easily reversible.

However, right now there are quite a few good top-level non-arXiv tags (e.g. derived-categories or soft-question) and there could be more in the future. What to do with them?

There are several possible choices of action -- none is terrible from my point of view, but I would say the topic deserves a top-level post and some thought going into it.

I suppose that if Terry Tao asks a question on MO, he could use it ...

1. They cover just about every possible topic in a small number of tags. (Insert mandatory joke about compactness here)
2. They don't change. (Too often)
3. They are used.

So far I've answered far more questions than I've asked so I'm much more concerned with tags from an answerer's point of view, in which case I just want to bookmark some tags and then forget about them. So I don't care what they are, so long as they select the right topics. If everyone tags their topology questions with "Teapots" then I'll bookmark "Teapots" and be happy.

I'd argue that being unfamiliar with the arxiv correlates pretty well with not being ready for MO

I'm not familiar with arXiv in this sense, since I only remember a few easy subject areas, like AG, NT, LO, RT (this already has a potential a confusion between Representation Theory and Ring Theory). In my opinion there is a clear benefit of allowing people like me to easily recognize all areas by a long name.

Currently, lots of activity happen under derived-category, homological-algebra and soft-question tags which won't fit arxiv-style but seem to me to be valid top-level tags. Next year, the top tags could be different. There's a gain in not tying our hands to arXiv unless the benefits of such a move are proven.

Combine multiple words into single-words, space to separate up to 5 tags (algebraic-geometry logic numerical-analysis)

Please try use at least one of the tags describing arXiv subject area: algebraic-topology for math.AT, dynamical-systems for math.DS, logic for math.LO, and so on, or a similar widespread tag, such as derived-category, tqft or soft-question. For more on how to tag you question effectively, consult this Tagging Guide (via meta.SO)

Annoyingly, I only have control of the text between the first open paren and the last close paren.

Combine multiple words into single-words, space to separate up to 5 tags (algebraic-geometry logic numerical-analysis
Please use at least one of the arXiv subject area tags:
algebraic-geometry algebraic-topology analysis category-theory combinatorics commutative-algebra complex-variables control-theory differential-geometry dynamical-systems functional-analysis topology geometric-topology group-theory information-theory k-theory homological-algebra lie-algebras lie-groups linear-algebra logic mathematical-physics metric-geometry number-theory numerical-analysis odes operator-algebras optimization pdes probability qft quantum-algebra representation-theory ring-theory spectral-theory statistics subfactors symplectic-geometry tqft derived-category geometry)

Which I would change to

Combine multiple words into single-words, space to separate up to 5 tags (algebraic-geometry moduli-space k3)

Please try use at least one of the tags describing arXiv subject area: algebraic-topology for math.AT, dynamical-systems for math.DS, logic for math.LO, and so on, or a similar widespread tag, such as derived-category, tqft or soft-question. Consult Tagging FAQ for more info.

http://mathoverflow.net/questions/tagged/commutative-algebra examples

(Aside: you can also use the search box to do this. For example, a search for "[commutative-algebra] [algebraic-geometry] stack" will produce a list of questions that use those two tags and contain the word "stack". Annoyingly, if your search only contains tags, then you get a broken link. If you replace all the +'s in the broken URL with spaces, it works as expected.)

If I retag something, it's likely to be because I want to be able to find it this way later.

Seriously, a hierarchy of tags could easily be implemented. Whenever a user puts in a tag that hasn't been seen before, they are asked for a "parent" tag. Since they created the new tag, they have a vested interest in making sure that it fits in well with the current tagging system. So there'd be no need for an automated system.

However, the hierarchy is pie-in-the-sky as I guess that it would involve deeper coding than you have access to. The serious point is that when looking for a good implementation, it can be useful to look from both directions, even if the "ideal" (whatever that is) is unachievable.

A system that would be implementable would be to insist on at least one "top level" tag for each question. "Top level" could correspond, roughly, to the arXiv classification, I guess. I know nothing about javascript, but presumably it would be easy to check if such a tag is selected and prompt for one if not.

On a slightly different note, I have to confess that I don't really understand what the tagging system is for. I mean, I have a vague idea but that's not really enough for me to select the right tag. As a questioner, the point of the tags is to make sure that my question is seen by someone likely to know the answer. Of course, the strategy then is to select all tags! But I acknowledge that if everyone did that, the system would become useless. So I need to select more carefully, but to do that I need to know how people are using the tag system from the other end. And that I don't know. At the moment, the number of questions is low enough that I'm using the tags merely to highlight potentially interesting questions. Later on, I may start seriously filtering by tags and ignoring anything, say, with [algebraic-geometry] on it. But I have no idea whether or not anyone else is using them this way, or maybe in a different way. Some people might be fairly restrictive: after all, my true area of expertise isn't all that large so if I restricted solely to that then I'd only check one or two tags. But my wider area of "knowing a bit more than the average mathematician" is much broader so I probably ought to be checking in this category. What are other people doing?

I guess ideally one would be able to define a hierarchy of tags so that [topology] "owned", say, [homotopy theory] and searching by a high level tag brought up all the lower ones as well. This would make sense outside mathematics - has anything like it been tried on the other SE sites?

I'm pretty sure it hasn't been tried on any SE site (there's no support for it) or on the main S[OFU] sites. The problem I have with this approach is that it doesn't seem sustainable. When somebody creates a new tag, how should it be decided which tag "owns" it or which arXiv tag it "retracts onto"? I feel like tagging is fundamentally something for humans to do; it's how we humans do our part to help out with things computers are bad at. Given that humans have to be involved in tagging, I think it should be kept as simple and non-hierarchical as possible. If the tagging system becomes something more complicated than what it is now, even fewer people will put in the 15 seconds it takes to use tags properly or retag a question because they don't understand the system. Low barrier to entry is absolutely essential for crowd-sourcing.

I don't mean to say that we shouldn't aspire to have a better tagging system, but if we're going to do something fancy, it had better be for a really good reason, not just because it sounds good. It's easy to get carried away with a beautiful architectural idea of how vast amounts of data should be organized, forgetting that you have to continuously maintain it and incorporate new data.

@rwbarton: I think it makes sense to retag something if one of the top answers uses a concept, even if the original question doesn't mention it.

@Scott and @Ilya: I've modified the ask page to include the following text under the tags box, but I don't think it's very good. How should it be modified?

Please use at least one of the arXiv subject area tags: algebraic-geometry algebraic-topology analysis category-theory combinatorics commutative-algebra complex-variables control-theory differential-geometry dynamical-systems functional-analysis topology geometric-topology group-theory information-theory k-theory homological-algebra lie-algebras lie-groups linear-algebra logic mathematical-physics metric-geometry number-theory numerical-analysis odes operator-algebras optimization pdes probability qft quantum-algebra representation-theory ring-theory spectral-theory statistics subfactors symplectic-geometry tqft derived-category geometry

If people have suggestions for tags that should be merged or renamed, please post on the Tags to Merge thread.

I like Ilya's idea of making a retagging FAQ. I, for example, don't feel entirely comfortable with the tagging system; it feels a little too chaotic to me, and I wish there were some rules (or at least heuristics) I could easily apply. The meta.SO tagging FAQ Ilya linked to is pretty good. The problem is that I'm not sure where to put a FAQ. I feel like there should be a way to use meta.MO to run a wiki-like FAQ. Poking around the settings, I see that it's possible to create roles that only have access to certain categories. It would be nice to make a FAQ category and give forum members the ability to edit posts within that category, but I don't see how to do that. If somebody knows how to do this, please let me know.

I think there are three things to be done:

• tag system could be clarified, and perhaps a list of top-level tags (extending the above) inserted into FAQ
• people can write a canonical retag FAQ, similar to the one at SO
• users with >500 rep should be reminded they can retag

Still, I would not expect that people who ask questions can tag them properly -- often knowing the correct classification would be a big part of an answer! Rather, I would enlist help from 50+ users who currently have the ability to retag (it's a good topic for a separate FAQ for them)

Perhaps the tags should be hierarchical. So if someone asks a specific question on, say, spectral sequences then it gets tagged "spectral-sequences" but also tagged "homotopy theory" and "topology". Then by following "topology" I get all questions of a topological nature and don't have to keep track of sub-fields and the like.

One question I have is, if a question does not directly mention a concept, but the (or an) answer does, does it make sense to later tag the question with that concept? e.g. r-matrix here, or maybe spectral-sequences here.

I don't know if this is quite the right place for this, but I notice that we now have tags "supersymmetry" and "super-linear-algebra". The latter is very specific, and the former seems to mean something specific to physicists which isn't quite what the questions without that tag are about. Rather than create "super-linear-algebra", "super-algebra", "super-manifolds", etc., maybe just go with a single tag "super-stuff"?

It's a good point that tags are underappreciated. My guess would be our users are still able to read all questions, so people don't uses the list of questions under given tag that much. I don't use it a lot either, though I use tags for highlighting ofinteresting and skipped questions in the question list.

I hadn't noticed that it was Pete's first question (he has done a lot of answers and has been on the site for 2 weeks), but that's certainly not the only example. Another good one I just retagged is Qiaochu Yuan's which was about interpreting super-vector spaces in terms of Hopf algebras, and didn't use the quite well-established tag for "hopf-algebras." Qiaochu is about as active and engaged as user as we have, so it worries me if he's not using tags like that.

By the way, I remember I heard once that Community User automatically retags some questions. Do we have it on MO?

How do we encourage people to use better and more specific tags?