The approach of Linked Geo Data is to store the mapping information in a relational database (Post GIS) together with the OSM data, and use Ontology-based Data Access (OBDA) tooling for generating the RDF.
The LinkedGeoData SQL Scripts extend a simple schema flavoured OSM data with additional indexes, tables and views. Note, that these extensions are designed to be 100% compatible with Osmosis replication (aka live-sync) features.
The following Mapping Tables are used to relate the OSM tags to corresponding RDF resources:
lgd_map_datatype(k, datatype): Values of the given keys should be interpreted as members of a certain datatype (boolean, int or float).
lgd_map_literal (k, property, language): Values of the given keys are treated as plain literals having the specified language tag.
lgd_map_resource_k (k, property, object): The presence of a key yields triples with the given property and object.
lgd_map_resource_kv (k, v, property, object): Similar to above, except that the value is also taken into account.
lgd_map_property (k, property): Relates keys to corresponding properties.
The LinkedGeoData RDB2RDF Mapping is then used to map the relational OSM database to RDF.