There is a wiki page on the Roller Wiki where some of these ideas were
discussed before and maybe this should move back there.
http://www.rollerweblogger.org/wiki/Wiki.jsp?page=BetterWeblogCategorizationForRoller
I find myself mostly in agreement with Allen here but here is my
personal take.
With hierarchical categories, I always seem to find myself at some point
faced with the problem of deciding which category is the superior of two
in the tree. Do I organize some stuff as tips/java and tips/linux or
java/tips and linux/tips? Decisions change in the presence of other
related topics at a given level (suppose I add dotnet), and one's
decisions may change over time. Hierarchy is an organizational choice
about the overall space of entries and not really a property of an entry
itself, which is simply that it is, say, both "tip" and "java", whether
I organize that as "java/tips" or "tips/java".
I concur with Allen that multiple category assignments are further
complicated by hierarchical categories, not necessarily in
implementation but certainly for users. Mostly, this comes from the
expectation that entries in a subcategory belong also to the parent
category. I think combining this with multiple categories makes the
organizational problem even harder for users.
I* *believe that we can address both of these issues by supporting a
flat ad-hoc namespace of "tags" which users can easily assign to entries
(any number to an entry), combined with a concept of filter-based
folders that use indexes on tags. Folder contents would be dynamic,
defined by search filters on your tag space.
If you want hierarchy, subfolders can translate into sub filters
(interpreted as conjunctions on the parent folder's filter). For
example a "java" category could be based on a filter for entries with
tag "java" while the subfolder "java/tips" could be defined by the
additional filter "tips" (applied, conceptually, to the result of the
query in the parent folder; in practice this would just be a
conjunction: "tips" and "java"). The same filter "tips" used at the top
level would yield a folder that contains all entries tagged with "tips".
Filter-based folders would allow you to change the organization, even
flip hierarchies without actually moving/changing anything but the
folder definitions.
A few additional comments.
(1) One may want to distinguish between "global" or "public" tags
(folksonomic classfications) which are intended to make sense in a wide
setting, for example, to match what someone else might be searching for
and which may be useful to sites like Technorati, and "local" or
"personal" tags (personal taxonomies) which are really only for
interpretation in a very local context. People make category names of
both varieties. For example, in my little blog, I use the category
"chow" for food/restaurant-related stuff and "System.out" for
miscellany. These can still be tags, but they are not useful ones, and
may even be confusing ones to use in a public setting.
(2) Tags can be more generic attributes than topic. The location-based
tags on sites that Flikr supports are a prime example. I think we
really need to understand these concepts and the types of functionality
people will want to use in the broader setting of blog search and
aggregation. I think such considerations could affect our thinking
quite a bit.
(3) Ease of tagging is extremely important, preferably these could be
typed as text with some minimal markup right in the entry (as was the
case with my primitive topic tag page plugin). I think this is really
important. Pull downs and selection boxes seem too painful, but I may
be in the minority here.
