Information technology - International Standardized Profiles FVT3nn - Virtual Terminal Basic Class - Register of attribute assignment type definitions - Part 3: FVT312 - Repertoire assignment type for ISO/IEC 2022 Level 2
The concept of Profiles for OSI, and the structure of the International Standardized Profiles that document them, are defined in ISO/IEC TR 10000-1. Such Profiles are divided into a number of different classes and sub-classes. Two of these classes contain sub-classes comprising functions of the Virtual Terminal Basic Class Service and Protocol specified in the base standards ISO/IEC 9040 and ISO/IEC 9041. These are the Application Profiles (A-Profiles) and the Interchange Format and Representation Profiles (F-Profiles).
The relationship between A-Profiles and F-Profiles is described in 7.3.2 of ISO/IEC TR 10000-1 and is as follows. Application Layer base standards require, implicitly or explicitly, the structure of information carried or referenced by them to be specified for each instance of communication. It is the purpose of F-Profiles to specify such information structures. Particular functional requirements may then be met by the combination of an A-Profile with one or more F-Profiles.
Establishment of a VT-association involves the selection by negotiation of a particular Virtual Terminal Environment profile (VTE-profile), and of particular values for any arguments of that VTE-profile. The VTE-profile specification, and possibly also the values of certain VTE-profile arguments, may in turn reference the definitions of VT control object types and attribute assignment types. These VTE-profiles, control object types and attribute assignment types are therefore Information Objects that require explicit reference within the VT protocol. Particular instances of these Information Objects are fully defined within the base standards, but the base standards also provide for further instances to be defined by registration. Each registered instance constitutes an F-Profile within the framework of ISO/IEC TR 10000.
The Virtual Terminal Basic Class Service and Protocol may be used to realise a wide range of distinct functions. Particular functions may be realised through the selection of appropriate VT functional units, F-Profiles and other, VTE-profile argument values. The specification of the selection required to realise a particular function and to promote interoperability constitutes a Virtual Terminal A-Profile within the framework of ISO/IEC TR 10000.
The three International Registers of VT information objects and the specifications of VT Application Profiles are each published as a separate multi-part ISP as follows:
— ISO/IEC ISP 11184 is the Register of VTE-profiles;
— ISO/IEC ISP 11185 is the Register of control object type definitions;
— ISO/IEC ISP 11186 is the Register of attribute assignment type definitions;
— ISO/IEC ISP 11187 contains the specifications of VT Application Profiles.
This part of ISO/IEC ISP 11186 contains the definition of a repertoire assignment type for which a repertoire assignment value identifies the use of a level 2 version of the 8-bit code structure of ISO/IEC 2022 (multiple pre-designated character sets, without locking shifts). Such a version of ISO/IEC 2022 provides access to G2 and G3 code elements, in addition to the GO and G1 code elements that may be accessed by means of the default repertoire assignment type specified in ISO/IEC 9040.
This repertoire assignment type also includes provision for restriction of the repertoire of characters to a subset of those that can be represented by the selected version of ISO/IEC 2022. The restriction of the repertoire may be by means outside the scope of ISO/IEC 2022. In particular the repertoire may be specified according to ISO/IEC 10646-1 even though the coding for information interchange is according to a level 2 version of ISO/IEC 2022. This facility should assist interworking during migration of applications from ISO/IEC 2022 coding to ISO/IEC 10646-1 coding.
NOTE 1 The use of locking shifts within the code structure of ISO/IEC 2022 is not consistent with the concept of a character-repertoire as defined in ISO/IEC 90