Lots, and it mostly boils down to "tags work a lot like they do in most other online systems". A few points:
-- Tag values can be added at runtime, at will.
-- Tags are text, but very limited text. (Pure alphanumeric plus spaces; for technical reasons, I may not allow more than that. Essentially, they have the same restrictions as Thing names, so that they may easily be placed inside URLs. Ordinary text, by contrast, is extremely free-form, and much more powerful.)
-- Tags are (optionally) hierarchical; eg, a period recipe Space might have the tag "Sources/16th century/Scappi".
-- The UI of a tag will encourage you to reuse existing tags, rather than inventing new ones willy-nilly.
-- A tag is automatically clickable: clicking on it brings you to a page that lists all Things containing that tag in this Space.
-- Those pages can be customized. (Technically, a tag can be reified into a Thing simply by editing it.) This is intended so that you can add additional details and semantics describing this tag.
So they are *kind* of like short text fields. They're very restricted in the text you can put in them, but they have additional features intended to make them useful for run-time categorization. They are *intended* for categorization, and everything will be optimized for that use case. But "categorization" is a loose enough concept that I expect the reality to be somewhat fuzzy.
Or to put it another way: a collection of tags is intended to be a hierarchical collection of *names*. Regardless of design intent, that is technically what they basically are. (But note: each Thing has an official Name property built in. Tags are not a replacement for that, and basically can't be used as such. Rather, they are other names that are, in some form, relevant to this Thing.)
no subject
-- Tag values can be added at runtime, at will.
-- Tags are text, but very limited text. (Pure alphanumeric plus spaces; for technical reasons, I may not allow more than that. Essentially, they have the same restrictions as Thing names, so that they may easily be placed inside URLs. Ordinary text, by contrast, is extremely free-form, and much more powerful.)
-- Tags are (optionally) hierarchical; eg, a period recipe Space might have the tag "Sources/16th century/Scappi".
-- The UI of a tag will encourage you to reuse existing tags, rather than inventing new ones willy-nilly.
-- A tag is automatically clickable: clicking on it brings you to a page that lists all Things containing that tag in this Space.
-- Those pages can be customized. (Technically, a tag can be reified into a Thing simply by editing it.) This is intended so that you can add additional details and semantics describing this tag.
So they are *kind* of like short text fields. They're very restricted in the text you can put in them, but they have additional features intended to make them useful for run-time categorization. They are *intended* for categorization, and everything will be optimized for that use case. But "categorization" is a loose enough concept that I expect the reality to be somewhat fuzzy.
Or to put it another way: a collection of tags is intended to be a hierarchical collection of *names*. Regardless of design intent, that is technically what they basically are. (But note: each Thing has an official Name property built in. Tags are not a replacement for that, and basically can't be used as such. Rather, they are other names that are, in some form, relevant to this Thing.)