3 ms·

> Another way to put this is that categories have to be typed: a category contains either (just) articles, or it contains (just) categories. The problem with u

> Another way to put this is that categories have to be typed: a category contains either (just) articles, or it contains (just) categories. The problem with using such a strict type system as a tagging-system is exacerbated by the cases where: 1. Someone adds an article to a category (they tag the article), but then want to add a subcategory to that category. Now the category contains both articles and subcategories (violating the constraint). So the user would have to move all its articles into its subcategories for the constraint to be satisfied. This can be an enormous amount of work (needing to invent new subcategories for all the articles in the category not fitting into the specific subcategory they had in mind). 2. Someone wants to add an article, but only has a vague idea of a super-category in which it would fit. Now they have to exhaustively crawl/navigate the tree of sub-categories, until they find only the leaf sub-categories which only contains articles, which is a place they could put it. The input barrier thus becomes high (which is antithetical to how people expect to use tags).

layer8 4y ago
Re 1: I think you misunderstood. The restriction of either articles or categories is for the instance-of relation. (The subset-of relation is naturally restricted to categories to begin with.) If a category contains articles, it can’t also contain categories as elements (instance-of relation). But it can contain subcategories as subsets. Analogy: The set of real numbers has the set of natural numbers as a subset, but it doesn’t have the set of natural numbers as an element, because the set of natural numbers is not a real number — the individual natural numbers are. Likewise, the category “Occupations” may contain articles describing occupations, and it may have a subcategory “Clerical occupations” (subset-of relation), but it cannot contain the category “Writers” as an element (in an instance-of relation as with the articles), because writers are not a subset of occupations. Furthermore, as an example of a meta-category, the category “Categories with more than 100 entries” may contain the category “Occupations” as an element (but not as a subcategory!), and hence cannot contain any articles as elements. The element type of the category “Categories with more than 100 entries” is categories, and the element type of “Occupations” is articles. The point is that you can’t mix both types of elements within the same category. This is independent from subcategories. Any category can have subcategories, the only condition being that the subcategories must have the same element type as the suoercategory. The idea is that a category can have both subset-of and instance-of relations at the same time (and each relation needs to be marked as such in the system), but the instance-of relation is restricted to be either articles or categories, but not both. Re 2: I believe that problem goes away, given the above.

layer8 4y ago

Re 1: I think you misunderstood. The restriction of either articles or categories is for the instance-of relation. (The subset-of relation is naturally restricted to categories to begin with.) If a category contains articles, it can’t also contain categories as elements (instance-of relation). But it can contain subcategories as subsets. Analogy: The set of real numbers has the set of natural numbers as a subset, but it doesn’t have the set of natural numbers as an element, because the set of natural numbers is not a real number — the individual natural numbers are. Likewise, the category “Occupations” may contain articles describing occupations, and it may have a subcategory “Clerical occupations” (subset-of relation), but it cannot contain the category “Writers” as an element (in an instance-of relation as with the articles), because writers are not a subset of occupations. Furthermore, as an example of a meta-category, the category “Categories with more than 100 entries” may contain the category “Occupations” as an element (but not as a subcategory!), and hence cannot contain any articles as elements. The element type of the category “Categories with more than 100 entries” is categories, and the element type of “Occupations” is articles. The point is that you can’t mix both types of elements within the same category. This is independent from subcategories. Any category can have subcategories, the only condition being that the subcategories must have the same element type as the suoercategory. The idea is that a category can have both subset-of and instance-of relations at the same time (and each relation needs to be marked as such in the system), but the instance-of relation is restricted to be either articles or categories, but not both. Re 2: I believe that problem goes away, given the above.