RDF mapping

(This has nothing to do with Geographic "mapping" - its about tagging data fields with common, universal identifiers)

A stub that emulates what D6 rdfcck was trying to do, and what D7 RDF UI now
does.

This adds a UI and internal data management store for giving Drupal content
types and CCK fields recognisible, portable field ids, in RDF format.
(CURIEs)

As in D7, a forum post can now be mapped to rdf:type=sioc:Post and
Drupal $node->user can be mapped to dc:Creator

It only provides an internal API and CRUD for this mapping - it doesn't have
any effect on node data or presentation itself. That should be done by other
modules, such as an RDFa renderer or XML exporter.

Currently, this mapping can be used by the Freebase_CCK schema importer and
the Freebase_data importer.

This is Drupal 6 only - this sort of functionality already exists in Drupal7

@author 'dman' Dan Morrison http://coders.co.nz/
@version 2011

Background

The D6 development branches of the RDF module family were continually
unstable, and developed circular references on extended modules (eg sparql)
that were unneccessary for this single task.

The POINT of this remake of rdfcck was to reduce the multi-fingered
dependencies on other parts of the RDF module family. Just save a few
simple data mapping arrays for my content types and fields.

This module is a stub that backports part of the eventual solution used in D7
(entities and bundles etc) to make it available under D6.
The notation used is modelled closely on that used in D7 for entity info,
Just the [entity][bundles][{instance}][rdf_mapping] subset of D7 entity
definitions. Code built against this module should find the same data
structures avaialable when ported to D7.

The storage of this mapping data is just done in the variables table, as
- There is a lot less code overhead
- This work is already done in D7, this is a proof-of-concept backport.
- Most sites have need for only a handful of content types, so we won't
worry about scaling.
- For many use cases, if you are going to be using this feature at
all, you are probably going to load it every page anyway, so in
the variables cache is as good as anywhere.

This utility was created to support (and is only used by) cck_importer and
freebase_api