OneDbf:Rel: read-only: array
  Databese file relations decscription:
  Rel:={}
  AAdd( Rel, {cKey,cAlias,nOrder} )
  ...
  Where:
  cKey   - is the key expression as text string, when databases are
           connected it is SEEK command after this expression executed
  cAlias - is the workarea for SEEK
  nOrder - active index order in active ALIAS workarea