I realise that it’s been some time since this thread opened, but if the topic of tagging is still being discussed may I add a comment.
I’ve searched the entire forum, but it appears nobody has thought of using the model employed by WordNet as a structure for defining tags; I would recommend taking a look, not least because it is very well tested.
For those who may not have encountered it, WordNet is in essence a structure for defining natural language concepts – words, phrases – and relationships between them. Think of it as a “metamodel” for language (not just English, any language). We describe everything using language, so the meta model concepts are generalisable to all fields of endeavour. WordNet is (indeed cannot be) complete in respect of every discipline – history, medicine, biology, chemistry etc. – but it can be extended into them without having to add to its “language metamodel”.
From the point of view of tagging, the key elements of WordNet that I would focus on are synonyms, parts of speech, hyper- and hyponyms, and mero- / homonyms. There is more, but all tags I have come across relate to either things (the tag is a noun) or actions (the tag is a *verb) and these concepts suffice. If there are live examples of parts of speech other than nouns and verbs being used as tags I’d like to hear about them.
WordNet recognises that the same concept may be described different words, i.e. synonyms. In fact its core construct is the “synset”, the group of words that all describe the same thing. A big part of the problem with tagging as an information discovery tool is that different people at different times use different synonyms for the same concept. When we are looking to find something we are basically asking the question, what do I know about X? X is a concept, like a ship or a fight or a battle, not necessarily any specific term (word). In Logseq a tag is a note, and a note can easily define synset (i.e. a list of words), it ought to be relatively straight forward to identify the note containing the given “tag word” and link to it rather than straight to a note having that word as its title.
Words, of course, may have multiple meanings. English (for example) freely uses nouns as verbs; there is a big conceptual difference between a fight and to fight or a fly and to fly. Synsets have descriptions of the concept they define (there are four for fly as a noun and 14 for fly as a verb!). Tagging to the synset rather than the word resolves the ambiguity making subsequent query more precise.
Hyper- and hyponyms are respectively generalisations and specialisations of concepts. Thus “dog” (in the sense of a member of the genus Canis that has been domesticated by man since prehistoric times; occurs in many breeds) has “canine” (any of various fissiped mammals with nonretractile claws and typically long muzzles) as a hypernym and various breeds of dog as hyponyms. Importantly, WordNet differentiates between a concept and an instance of that concept. “Labrador Retriever” is a hyponym of “dog”; my dog “Pepper” is an instance hyponym of “Labrador Retriever”.
Finally – at least from the perspective of tagging – WordNet describes mereological (i.e. part-part of) relationships; thus the concept of an (internal combustion) engine has part meronyms of camshaft and cylinder. Cylinder and camshaft have engine as their holonym.
Anyway, a suggestion that I feel is worth investigating further.