A subclass of a category which is itself a category, whose arrows are a restriction of the arrows of the parent category, and whose composition rule is a restriction of the parent category's
A subcategory is a named collection of data items within a category Subcategories are used to indicate a special subsets of data items For instance, the data items _atom_site Cartn_x, _atom_site Cartn_y, and _atom_site Cartn_z belong to a subcategory named cartesian_coordinate
A category that is a more specific part of the category that contains it For example, a category called "Departments" might contain subcategories called "Engineering," "Finance," and "Marketing "
A subject category that is more narrowly focused than the broader subject category above it in a hierarchy
A subclass of a category which is itself a category, whose arrows are a restriction of the arrows of the parent category, and whose composition rule is a restriction of the parent categorys