code: public TableDefinition getLinkExtentTableDef(FieldDefinition linkDef) {
          assert linkDef != null;
          assert linkDef.isLinkType();
          assert m_appDef != null;
          
          TableDefinition tableDef = m_appDef.getTableDef(linkDef.getLinkExtent());
          assert tableDef != null;
          return tableDef;
      }
docs: Get the TableDefinition of the "extent" table for the given link field.
  
  @param  linkDef  {@link FieldDefinition} for a link field.
  @return          {@link TableDefinition} for link's extent (target) table.