|fields||n/a||This property is always required.|
|fields_cache||n/a||This property is always required.|
Each subfield within a compound field has its own table named <dataset>_<fieldname>_<subfieldname>. For example, the related URL for an EPrint (related_url) has a URL and a type, so would have tables named eprint_related_url_url and eprint_related_url_type.
The tables in this instance have the following structure:
eprint_related_url_url: eprintid INT(11), pos INT(11), related_url_url VARCHAR(255) eprint_related_url_type: eprintid INT(11), pos INT(11), related_url_type VARCHAR(255)
eprintid is the ID of the EPrint to which the field applies, pos contains the position of the entry (starting at 0), and the remaining field uses the appropriate field type for the subfield (in this case VARCHAR(255) for both URL and type).