It is impractical to create a centralized metadata store for the web.
However, we need shared metadata to make the web easier to get around in. XFML takes a distributed approach, yet allows individual authors to connect their metadata schemes by merging topics. Thus it allows for creation of a distributed, loosely connected metadata network that fulfills much of the same functions a centralized store would.
Taxonomies are labour intensive to create.
XFML allows taxonomies to be easily shared and published.
Faceted taxonomies are generally more powerful for websites than classic hierarchical taxonomies.
XFML is based on facets.
Taxonomies are created by fallible humans and subject to change.
XFML is based around imperfect and ever changing taxonomies: with its strict separation of metadata and content, the metadata in an XFML map can evolve more easily than in most current cms systems where metadata is intertwined with content definition, and where adjusting the structure of the metadata typically involves a lot of work.
Most current content management systems implement a certain level of metadata already, yet there is no standard way of publishing this metadata, let alone make meaningful connections between metadata in different systems.
Allowing meaningful metadata connections between separate systems is what makes XFML so powerful.
