Documentum systems has two views for single and repeating attributes these are _sv and _sp for single attributes and _rv and _rp for repeating attributes.
dm_document_sp, dm_document_sv, dm_document_rp, dm_document_rv
The two _sp and _rp views are used by DQL and the two
_sv and _rv views are used by the Object Manager. Also, the _sp and _sv views are for single (non-repeating) attributes, while the _rv and _rp views are for repeating attibutes.
In case you require to query the table rather than the object use the _sp,_rp views rather than making your own joins between _s or -r tables up the inheritance hierarchy.