code: public Index open(Transaction tx) {
  		TableInfo ti = VanillaDb.catalogMgr().getTableInfo(tblName, tx);
  		if (ti == null)
  			throw new TableNotFoundException("table '" + tblName
  					+ "' is not defined in catalog.");
  
  		return Index.newInstance(this, new SearchKeyType(ti.schema(), fldNames), tx);
  	}
docs: Opens the index described by this object.
  
  @param tx
  the context of executing transaction
  @return the {@link Index} object associated with this information