GeneralString vs VisibleString in GRS

Issue raised by: Mike Douglass Fri, 18 Jul 1997 12:34:25 -0400

InternationalString is defined as one of the possible ElementData types in GRS. This is defined as GeneralString with tag 27. There is some prose (in the body of the standard) referring to this collapsing to VisibleString when V2 is in force.

VisibleString (tag 26) is what some servers send me. Is this legal? If so, should the asn-1 for GRS-1 supply a tag value for this data type?

VisibleString (tag 26) is not supported by GRS and it is therefore not legal. Those servers sending tag 26 are in error.

The "collapsing" refers only to the character repertoire, not the asn.1 tag. It applies only to asn.1 identifiers from the 1992 version.

The intent of Z39.50-1995 is to depricate VisibleString. There are asn.1 identifiers from the 1992 version of type visibleString, so the 1995 version stipulates that when v2 is in effect (because if v2 is in effect one of the two systems may be based on the 1992 version), those parameters are restricted to the visibleString repertiore. Choice of tag -- 26 or 27 -- fortunately is not an issue, in all but one or two cases, because these are defined as IMPLICIT, and in the cases where they are not, the 95 version makes an explicit CHOICE depending on version.

True, GRS-1 is intended to operate when v2 is in effect. But GRS encounters data elements (not asn.1 identifiers from the 1992 version) defined by tagsets and schemas based on the retrieval architecture developed for the 95 version. No server has built support for GRS based on the 1992 version, because there was no GRS in the 1992 version.