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    • CommentAuthorYemon Choi
    • CommentTimeJun 27th 2011

    I ask because I've only just noticed a few questions to which the tag has been newly applied, and I don't really see why the old "books" tag wasn't enough.


    I don't think we need it. I propose to merge [textbook-recommendation] into [books]. Any objectors please speak up.

    By the way, 10k+ rep users can see newly created tags. I try to go through them every now and then to clean up, but I see I let [algebra] get out of hand ... now I'm not sure what to do with it.

    • CommentAuthorDavid White
    • CommentTimeJun 28th 2011 edited
    I've seen quite a few questions on MO of the flavor "can you recommend a textbook to learn X," so there's certainly a market for textbook recommendations. That seems to be contained in "books," but "books" also contains questions like "I'm reading Y's book and can't understand the proof of Lemma Z" or "What books would you like to see written" or "If one was to write a book on topic W what sorts of things should be covered." I created the textbook-recommendation tag because I like questions of the first sort, but none of the latter sort. Then I went through some old questions I had on my favorite's list which were about textbook recommendations and tagged them with both. I figured something might pop up on meta about it.

    Anyway, I'm fairly new to this whole game, so I will of course defer to the experts, but I wanted to explain my logic at least. It's not clear to me when to draw a fine distinction between different topics which get lumped together, e.g. sheaf-theory vs. sheaf-cohomology. Since the number of questions grows every day I prefer to have those separated, but maybe others disagree. I also recently created "homological-dimension" because all the dimension questions were on topological dimension or Krull dimension and that's not what I work on. Another reason I originally created the "textbook-recommendation" tag was that the "books" tag didn't come up in the autocomplete when I started typing "textbook" into the tag field. So I assumed there was no tag related to textbooks. I can imagine others making this mistake if asking a question searching for a textbook. This may be why there are so many questions out there about books which don't have the "books" tag, e.g. the ones I tagged yesterday and others that I haven't found yet

    EDIT: I also tend to think "reference-request" is really broad. There's a difference between wanting a reference for a known lemma and wanting a book to learn from. I don't have the mathematical depth in fields outside my own to handle the bulk of "reference-request" questions, but I feel I have some sense of which textbooks are good to learn from in many fields. So I was thinking of retagging some reference-request questions with either books or textbook-recommendation. I'm curious as to what others think of that.
    • CommentAuthorDavid White
    • CommentTimeJun 28th 2011 edited
    Some of those "algebra" tags are from me. I figured it existed as a catch-all for when you don't want to make any assumptions on your ring. I can probably retag those to "noncommutative-algebra" since that seems a better place for them.

    EDIT: I guess only one was from me. Anyway, I retagged it and a couple others I'd read before. The rest can probably just be done in bulk since they all have other tags (making tag-removed unnecessary)

    I think the consensus around here is that clean-up activities like retagging should be minimally intrusive. Since retagging kicks questions to the top of the active queue, it would be best if you refrained from retagging outside the following situations:

    1. There is a strong need. In this case it might be best to contact the moderators first, or open a thread here on meta.
    2. The question is already near the top for some other reason (e.g., someone recently submitted an answer).
    @Scott Thanks, that sounds like a fine policy and now I'm glad I only retagged a couple of posts rather than a bunch. I keep my page organized by "newest question" rather than "active" and didn't really realize how annoying this bumping can be until this morning. I only just learned from an old meta thread that moderators can make massive changes to tags without bumping (otherwise I wouldn't have gone and retagged those algebra posts above).

    I'm still curious to hear more about drawing fine divisions with tags vs. reducing the total number of tags. I'm especially curious about the new tags I created textbook-recommendation vs. books, and homological-dimension vs. dimension-theory. I looked into the dimension theory tag and it seems to be spread all over the place. I'd prefer to pull krull-dimension away from hausdorff-dimension for example but in this tag they're lumped together.
    • CommentAuthorYemon Choi
    • CommentTimeJun 28th 2011

    I think there is a case for having either the "books" tag or the "textbook-recommendation" tag, but not both. I also don't believe in trying to fine-tune the tags, except for cases such as those David has mentioned (homological-dimension vs topological-dimension; I don't think one should have a "hausdorff-dimension" tag because there are other notions of topological/metric dimension and I don't want separate tags for all of them). For that reason I don't really want a divide between sheaf-cohomology and sheaf-theory; I would personally use both the tags "cohomology" and "sheaf-theory".

    By the way, I view the "reference-request" as being exactly that, and not a "book-recommendation" tag.

    Some random thoughts: 1) I find it far easier to use Google to search MO than to use MO to search MO, myself. 2) since I use MO almost exclusively through the "active" page, bumping of old stuff tends to jar me.

    • CommentAuthorDavid White
    • CommentTimeJun 28th 2011 edited
    Hi Yemon,
    I was checking throughout the day wondering if you'd come back on. We seem to keep orthogonal hours...I'm barely keeping my eyelids open right now. I agree that I wouldn't use reference-request for anything book related. It seems much more focused on papers. In terms of searchability, I use the highlighting feature so I only have to follow a few tags where I have some chance of successfully answering a question. If I follow reference-request, 90% or more of the highlighted questions are impossible for me to answer. Same goes for dimension-theory. That's why I was hoping some fine tuning of tags would occur. I can well imagine people in the future using this highlighting feature more and more as MO grows and it seems wise to have well delineated tags.

    As for the dimension issue, I would recommend having tags for dimension-theory (understanding that this means topological dimension), Krull-dimension, cohomological-dimension, and homological-dimension. This seems to cover the major ways I've seen to define dimension. I suppose if you wanted to reduce the number of tags you could do geometric-dimension and algebraic-dimension or something, but I'm always in favor of finer divisions over lumping things together. Anyway, it seems moderators have the ability to lump tags together but I imagine it's hard to pull them apart once lumped. My plan would be to simply retag any dimension questions that are already on the front page (as in Scott's comment above) to help distinguish between those asking for krull, homological, or topological dimension. What do you think of this plan?

    I'm sorry, but I'm going to bed now. I'll read anything you write and reply in 8 hours when I come back to work.
    • CommentAuthoran_mo_user
    • CommentTimeJun 29th 2011

    Using the site more or less in the way Yemon Choi described, I never paid too much attention to the tags. Sparked by this discussion I looked around a bit more. Here are my thoughts. (Some of what I write could be read as critizising others behavior; this is not my intention. I merely wish to describe my perception of the situation. I can well imagine and understand why the situation is at it is, and I also it is in no way problematic for me.)

    My general impression is that there are way too many tags (about a thousand).
    A key question to me is what is a good minimal size for a tag to make it useful as a tag. I see two and two half use-cases for a tag:

    1. Automatic filtering by tags as supported by the software.
    2. Easy access to all question with a certain tag.
    3. Tags as clearly visible keywords of a question.
    4. Searching.

    The last two are the half-one, as I do not consider them at so important. For the first, a well-chosen title / the first lines (that are visible without opening the question) can by and large fulfil this purpose. And for the latter, I do not really know, but the general sentiment seems to be that serching the site with Google is anyway the way to go.

    For 3. I actually do not really see any non-trivial lower bound for the usefullness, and it seems to me that various tags were (unfortunately) created in this spirit. However, as said I do not consider 3. as so important, and for 1. and 2. and also 4. I think there clearly is a lower-bound on the size, below which the tag is not really useful (and its existence is mildly harmful, on the one hand as it is more or less noise, and on the other hand and more importantly as the existence of, say, five too small, and thus in my opninion. not useful tags prevents the existence of one larger and thus useful tag).

    Let me elaborate on the first line of the preceeding pargaraph. Why is there, for example, a thanks-tag ? (To answer my own question, it seems somebody found it a nice idea to create it, and then it was never deleted. Both, in particular the latter, understandable, and locally no problem. But the accumulation of such things creates in the long run masses of tags.) To give a somewhat less extreme examples, there is dedekind-domain, prufer-domain, euclidean-domain, ufds, pre-schreier used in total (not individually!) ten times; and some are dually used so the number of question with such a tag should be a bit smaller still. In general, about a third of the tags was used less than 5 times, many even only once.

    For 1. and 2. I think everything that is not used at least somewhat frequently is not of much use; perhaps 20 rather more as lower bound (so roughly and adjusting a bit to later cretaion, used once every two weeks, and if I look for question with the tag I get a page full of questions). Even with 20, only a third of the existing tags would make the cut.

    To be cont.

    • CommentAuthoran_mo_user
    • CommentTimeJun 29th 2011


    Now, for the concrete suggestions:

    a. dimension-theory this tag was used slightly more than 30 times. (And there is homological-dimension, used 4 times, and cohomological-dimension used once). I think all this together is a fine size for a tag. True, it is used for topology and algebra, and some other things, but then in total there is perhaps one question every week with this tag, so, if one starts splitting this there is essentially never a question with each of the tags.

    b. reference-request and related. This is addmittedly a large tag, and in my opinion a bit overused (what I mean is, just to express that one would be happy with a pointer to a written source answering the question at hand, to me does not make using the referenc-request really justified). I thus can understand the wish to have a specific tag for more general requests regarding intoductory or expository writings on a given subject (as opposed to highly specific requests for individual results), which seems to be the intention of the textbook-recommendation tag. In some sense I thus find it useful, though books serves a similar purpose. However, I am not quite happy with the name, as it is too specific. To me a textbook is a quite specific type of (published) book. To give a very recent example involving this tag (and its creator). Yesterday there was the question 'Survey of Algebraic K-theory since 1980 ?', which was in search of an analog of a paper (30 pages) of Weibel on the development of alg. K-theory up to 1980. This was then additionally tagged textbook-recommendation and an answer was 'Handbook of K-theory' [as far as my limited understanding goes a fine answer]. So what is the problem? First, the question did not really ask for a textbook not even a book but it seems to me just whatever would contain the requested material in a well-organized and somewhat accesible form; whether a textbook, a handbook, a monograph, lecture noted (published or unpublished), a survey articel (or a couple of complementary survey articles)..., I believe was of no importance to the questioner; and, indeed, he expressed (neutral to pleasant) surprise that there was a book. Yet, also this book is not a textbook. So, while this might be a bit nit-picking this question did not really ask for the recommendation of a textbook.

    The point I want to make is that to me the precise meaning of textbook-recommendation is much more narrow then the apparently intended usage. Thus, I think, if this tag should continue to exists it should be renamed. (There is a similar issue with books for this purpose, but it is at least a bit broader, and more importantly already existed.) I do not really have a good name (and am not a native speaker): still a try, while this sounds odd it might be good to be found easily (when searching the tags) introductory-expository-survey-overview. Or reference-request-expository also for reasons of being found easily (by people already using reference-request).

    • CommentAuthoran_mo_user
    • CommentTimeJun 29th 2011

    Afterthought: Perhaps I should add, as this might get lost or not be really visible from what I wrote, that I do appreciate (from one user to another on a to some extent community moderated site) the effort of David White. And, in theory, I could see some merits of a sophisticated tagging-system. Yet, in practise, I am more than a bit worried that anything too complex will simply not be used properly/consistenly and then loose its usefulness and become (mildly) harmful instead.

    • CommentAuthorDavid White
    • CommentTimeJun 29th 2011 edited
    Hi an_mo_user,

    I'm glad someone at least is reading this thread and thinking about this issue. Regarding your four points above, I agree that 3 and 4 are less important features. I personally have used tags as a way to search (e.g. look at all questions tagged dimension-theory or homological-algebra) but that's because my interests are probably too broad and I was just searching for interesting things to read rather than a specific question. MO seems designed primarily for specific research questions and for that there is no doubt google is the better way to search. Anyway, my use of the tags to search is more in line with your point 2 than with point 4.

    As for coming up with a lower threshold on tags, I'm completely on-board with one caveat. If a tag has only existed for a short period of time (let's say less than 2 months) then it's unfair to kill it simply because it has only been used a few times. The existing large tags are attractors and because typing the first few letters of a tag brings up the five most popular tag names a new tag will probably get few uses until it gets more popular. Today I retagged a brand-new question ( with the cohomological-dimension tag (which I didn't create btw). I had to type all of "cohomological" before the autocomplete for this tag appeared as an option. So I can easily see why the OP didn't use the tag, because he/she probably didn't know about it. BTW my reasoning for the retag was as follows: I figured that if ever there was a question meant for this tag, then this would be the one, and if the tag gets destroyed later then this retag cost us nothing (it didn't bump a post since the post was brand new).

    The FAQ recommends tags be kept short (the above episode clearly demonstrates why), so I don't think introductory-expository-survey-overview is going to find much support. I guess I should also mention that you're probably right about the K-theory question. I was trying to only retag questions that had already come to the front page so as not to bump anything, but I was also trying to get that textbook tag into the realm where people might actually use it. It's probably a moot point since the moderators will probably just merge the two book related tags. This is not the worst thing in the world...I just hope people actually use the book tag (whatever it's name eventually is) when they ask about a book.
    I'm making this a separate post so people won't think this is just a dialog between me and an_mo_user.

    I want to think about balancing keeping tag names short vs. tags containing vastly different types of questions. As the number of questions grows and as people post more and more specific research questions it's clear our existing tags are going to be overloaded. Perhaps a solution would be to display more than 5 tags in the auto-complete field so that people would see more of the fine divisions when they try to tag their question. This would hopefully stop the "algebra" tag from existing as a catch-all.

    Another solution I propose is to make it so retagging doesn't bump questions to the front page. That way experienced users could silently retag and keep things organized. In other meta posts people have said no edit should be silent (i.e. all edits should bump things to the front page) for transparency reasons.

    I don't think retags have the same danger of someone coming on and editing your post to make you look bad. If someone creates a tag like "I'm a jerk" then the moderators would see it as a new tag using the link at the top of this page and would kill that tag. Now suppose someone who's just reached 500 rep and wants the taxonomist badge goes and creates a tag N which is a near duplicate of an existing tag T, then retags all the T questions with N. The moderators would also see this new tag had just been created, and could merge N back into T while also writing the user to explain this is not how MO works. Alternately you could just do away with the taxonomist tag since it doesn't seem to be doing any good anymore and it gives people incentives to this type of behavior. Or you could make it so that the minimum rep to retag is higher than 500, figuring that by the time a user reaches 2000 or 3000 they are more mature. Anyway, these are the only objections I can see to the idea of making retags silent. Does anyone have any other objections? Should I post this as a separate meta thread? Do we even have the power to make a change like the one I'm suggesting?
    • CommentAuthorYemon Choi
    • CommentTimeJun 29th 2011

    Just to apologize for not responding - I am leaving soon for a trip to the UK and am, like, so behind on writing-up/refereeing duties, man. I will try and get back to this with some more coherent thoughts at a later date


    David, I'm afraid we do not have the power to change the underlying software. However, I do not know about the particulars of the tag autocomplete box.

    The current tagging system, which involves an ArXiv designation for general area plus some keywords, has worked reasonably well for more than a year. As far as I can tell, we haven't run into serious scaling problems, and it doesn't seem to be a danger in the near future. The solutions you propose would be potentially convenient if they were possible, though.

    • CommentAuthorEmerton
    • CommentTimeJun 29th 2011

    Perhaps not surprisingly, there have been previous meta discussions on related tagging issues. I am thinking in particular of this one.

    Note in this discussion that several people were of the view that even very low use tags were still helpful and legitimate. Especially when used in conjunction with more catch-all tags, they can be very helpful. (I'm thinking of pairings such as [ag.algebraic-geometry] and [minimal-model-program]; the former tag serves as an indication of the general area of research, and is useful to everyone, while the second tag is probably not so meaningful to non-experts, but to someone who knows algebraic geometry, it immediately conveys strong information about the flavour of the question.)

    In any case, I share the sentiment that some others have expressed here, that it is probably futile to try to be too systematic; with a lot of contributors at different levels of experience, both mathematical and with regard to the site itself, there are bound to be some inconsistencies, confusions, and annoyances with tags. If even the AMS classification system is an ongoing source of dispute (and it is, with legitimate points both for and against its current form), I don't think that we can expect MO tags to be any better. Overall, they seem to be working pretty well as they are.

    • CommentAuthoran_mo_user
    • CommentTimeJun 29th 2011

    Dear Emerton,

    I would agree that many of the low-use tags individually are helpful, yet I also believe that in there totally they tend to cause confusion and/or inconsitencies.

    To illustrate my point, let me return to the rings/domains example: in itself I see nothing wrong with dedekind-domain, prufer-domain, euclidean-domain, ufds, pre-schreier, and also cohen-macauly-ring is fine, and perhaps over time we will get (or perhaps already have for some I did not check) the tags for, say, Bezout, Mori, Krull, Laskerian, gcd, Cohen-Kaplansky, Prüfer v multiplication, Prüfer star multiplication domains or rings. However, what I do find slightly unfortunate is that I believe none of the questions tagged with the above mentioned tags is tagged (in addition) with commutative-rings. [Reading the thread you linked to now completely, before I knew only the end-part, I learned that at somme point even this commutative-rings tags was at some point considered as to narrow and to be subsumed in ac.commutative-algebra, though some disagreed.] Faced with the choice of having them all tagged commutative-rings and not a more specific one and having them all tagged with a more specific one and not commutative-rings I prefer the former. (If they had both tags, well, I would not mind so much.)

    Now, I could tag them in addition with the commutative-rings tag, however as said above by Scott Carnaham, one should not do so. Thus, I might consider suggesting to merge them.

    In the very end, as said above, for me personally the tags are of little relevance. However, what I wanted to point out is that, in my opinion, tag-proliferation is not completely for free. And, I would thus appreciate if at least tags like the I believe recently created, by an experienced user by the way, 'misapplied' tag (I already have doubts regarding the usefullness of applied, but misapplied how will this ever be useful as a tag?) would not be created.

    @Emerton, thanks for that link...somehow I missed that in my searching. What I took away from reading those posts is that a lot of MO heavy hitters were involved in that discussion and the consensus was to remove tags which were effectively duplicates or typos or forgotten-hyphens, but leave tags that made fine divisions if someone well respected spoke up (e.g. character-sheaves vs. sheaves, tensor-categories vs. monoidal-categories). For this reason, I feel homological-dimension and even krull-dimension tags would be in keeping with the spirit that was decided there. On the other hand, Yemon seems to want fewer tags, even if this means they are less specific in filtering questions. Correct me if I've misrepresented your view. If scalability is really not an issue then the only question left is to find the balance between tag specificity (how finely they cut) and having too many tags.

    I admit that I don't know much about the ArXiV tagging system. If people are trying to mimic that system, then most of what I suggest is probably worthless and we'll probably end up with fewer tags than I consider optimal. I'm thinking about MO through a grad student's eyes, trying to figure out which tags are useful for sifting through the front page or finding old posts to find something of interest (without having a specific question you're interested in). The fact that commutative-rings was once considered too specific seems crazy to me since during my time here commutative-rings has been a very popular tag. This seems like evidence that MO users want finer divisions in their tagging. More evidence: the majority of posts in the thread Prof Emerton linked to seemed to say it's okay to have specific tags as long as they are not duplicates.

    I very much like the idea of fine tags combined with general tags (this is why my retaggings added both textbook-recommendation and books to the posts in question), but I think you need to give the fine tags time to find an audience the way commutative-rings has done. If they find no audience after awhile then I think it's fine to kill them off. This way you get to balance reducing the "proliferation of tags" while also allowing people to try out specific tags in conjunction with general tags (as Emerton suggests). For people who post questions with fine tags but no general tag or create "inconsistency and confusion" I think it's up to the community to retag while those questions are still new. Users catch on quickly to which tags are important to use, and if we catch those cases early we never need to spam the front page with retagging for the purpose of cleanup. Even if we kill a bunch of tags today new users will still create different ones when they post a question and experienced users will still need to fix it (hopefully soon after the question is asked). I'll wait till Yemon comes back and others have a chance to comment, but I don't think I have anything more to add at this point about my position.
    • CommentAuthorYemon Choi
    • CommentTimeJun 30th 2011

    There's a lot to digest and respond to from various people, which I sadly can't do properly right now. Hence this post of mine is going to be even less coherent than usual, I'm afraid.

    Yemon seems to want fewer tags, even if this means they are less specific in filtering questions.

    That's probably fair. I just don't see why the situation ``as people post more and more specific research questions it's clear our existing tags are going to be overloaded'' is a problem. If one were to start parsing the fine detail of the functional analysis tags we could easily create something like Borges's system with, IMHO, nothing gained. Since I don't search MO to find answers to questions (except to check that no one has already answered it) and I find Googling sufficient for my search requirements, I personally wouldn't gain from more precise taxonomy.

    I guess I still don't understand why one wants finer tags as a general principle, rather than something to do on a trial ad hoc basis. I don't think this is going to significantly affect the likelihood or speed with which someone's question is answered. (See my recent questions about finite groups: I am happy to have general tags and a hopefully specific question.) If someone tags a question "Banach algebras" and writes a clear, well-defined question, that's good enough for me, I don't really see how matters would be improved by having separate tags for "Gelfand theory", "Fourier algebras", "uniform algebras", "function algebras", "nonself-adjoint operator algebras", "radical Banach algebras", "strawberry flavoured amenability", "exponential spectrum", "Beurling algebras", "topological centres", "semigroup algebras", "group algebras", "pseudofunction algebras", "spectral synthesis", "operator synthesis", "Q-algebras", "dual Banach algebras", "measure algebras", "approximate homomorphisms", ...

    If someone has a question in algebraic topology related to spectra, do we need a tag for "spectra"? (Do we already have one?) If so then I agree one should differentiate between that and the spectrum of sp.spectral-theory, or the prime ideal spectrum; but I am not sure such specificity is needed.

    • CommentAuthorYemon Choi
    • CommentTimeJun 30th 2011

    (I should add that I have cared, to varying degrees, about all but two of the examples listed in the penultimate paragraph of my previous post, and those two exceptions are acknowledged topics of research which people are thinking about these days. So it wasn't a list of random obscure stuff, at least not in my mind.)

    I'd like to retract my statement that "as people post more and more specific research questions it's clear our existing tags are going to be overloaded." Others much more experienced than I have pointed out that scaling is not a problem. I'm also not advocating a massive shift in our tagging policy. Above I've mostly been trying to argue (and I hope it came across this way) that some people might want more specific tags and we should allow those as long as others in the community also use them. I personally would like to see more specific tags (e.g. I'm definitely in favor of a spectra style tag and I'm surprised it doesn't exist already), but I think the best way to get there is "on a trial ad hoc basis." If people start using specific tags without the big general tags, then more experienced users can retag to add the general ones and I don't think anything is hurt.

    My main concern was that moderators would come along and hammer a tag before it had any chance to get its own momentum. I haven't tagged anything with textbook-recommendation in several days and all the questions so tagged have left the front page. However, I'm pleased to report that this morning someone tagged a question with textbook-recommendation and so I'm hopeful this tag will gain some momentum. If we'd just merged it right away with books we'd never know. If it gains no momentum after a couple of months, then we should merge them because it's clear the community doesn't see the finer distinction as useful.
    • CommentAuthorquid
    • CommentTimeSep 14th 2011

    Hi David,

    since the textbook-recommendation tag just passed the taxonimist-badge-granting level (50+) I thought I'd use this opportunity to thank you for creating and (to a significant extent) mainting this tag, which in my opinion developped very well and became a useful addition to the tag-system.