ITU-T Recommendations

An Amendment 1 is provided for ITU-T Rec. X.680 | ISO/IEC 8824-1, ITU-T Rec. X.681 | ISO/IEC 8824-2, ITU-T Rec. 690 | ISO/IEC 8825-1, ITU-T Rec. X.691 | ISO/IEC 8825-2 and ITU-T Rec. X.693 | ISO/IEC 8825-4. These amendments provide the following:
– Correction of a bug in CXER resulting from allowing white-space between a minus sign and a following INTEGER or REAL value (CXER was not canonical). This is no longer permitted, in value notation, XML Value Notation or in XER and CXER. This is a change (introduced by text in Amendment 1 to Rec. X.680 | ISO/IEC 8824-1) and not an addition.
– Addition of encoding instructions in an ASN.1 module, using either a type prefix or within an encoding control section, in order to specify variations of the BASIC-XER encodings. These encoding instructions are designed to support mappings from an XSD specification to an ASN.1 specification. This provision has meant a change of terminology, where a type with "[…]" in front of it is a prefixed type, and the "[…]" notation may or may not be a tag. This change of terminology results in changes to the text (but not the substance) of the BER and PER specifications, so there is also an Amendment 1 to these specifications.
– The addition of NaN (Not-a-Number) and minus zero as new values for REAL (support for encoding these new values is provided in Amendment 1 to ITU-T Rec. X.690 | ISO/IEC 8825-1 and to ITU-T Rec. X.691 | ISO/IEC 8825-2, as well as in Amendment 1 to ITU-T Rec. X.693 | ISO/IEC 8825-4).
– The addition of new XML Value Notations for REAL, BOOLEAN, ENUMERATED, and INTEGER that use text rather than empty-element tags for the values. These are available in XML Value Notation and in EXTENDED-XER, but not in BASIC-XER (for reasons of backwards-compatibility).
– Changes to the XML Value Notation for sequence-of (and the XER encodings) to provide delimitation of values where they are not XML elements (this occurs with the additional XML Value Notations, and only affects use of those additional XML Value Notations). This change is only concerned with use of XML Value Notations that have been added by this amendment, and these are not allowed in BASIC-XER, which is not affected.
This provides the necessary basic support for EXTENDED-XER.
This amendment depends on ITU-T Rec. X.680 (2002)/Amd.1 (2003) | ISO/IEC 8824-1:2002/Amd.1:2003 and on ITU-T Rec. X.681 (2002)/Amd.1 (2003) | ISO/IEC 8824-2:2002/Amd.1:2003 for the provision of alternative encodings for some types and for syntax for the insertion of XER encoding instructions in an ASN.1 specification. Many references from this amendment to clauses in these Recommendations | International Standards are to clauses introduced by those amendments.
The bulk of this amendment is concerned with the specification of the syntax and semantics of (new) XER encoding instructions that can be used to require EXTENDED-XER encoders to provide specialized encodings for ASN.1 types. These specialized encodings are largely designed to support ITU-T Rec. X.694 | ISO/IEC 8825-5 (Mapping XSD into ASN.1).