Halliday & Matthiessen (1999: 82):
Categories are construed in the network of the ideation base in terms of different kinds of relations they enter into: [1] globally, they are construed in terms of taxonomic elaboration: they form part of a system that is located somewhere in delicacy within the meaning base; [2] locally, they may be construed in terms of meronymic extension: they may form part of a local meronymic taxonomy, such as the cat and its body parts; [3] transcategorially, they may be construed in terms of the rôles they play in some other type of category, such as cat serving in certain participant rôles of figures.