4. Classification Types
You can use 3 kind of Classification types:
A tag is a label attached to someone or something for identification or other information.
Usage: A blog post can have many tags.
A collection is a group of objects or works to be seen, studied, or kept together.
Usage: A blog post belongs to one collection.
A category is a class or division of things regarded as having particular shared characteristics.
Usage: A product available through a shop belongs to one or many categories.
A Context is a way to group Tag, Collection and Category into one set. So you can have duplicate tag accross contexts.