The following copyrighted Introduction and Scope of ISO/IEC 8211:1994 is included on this home page with the permission of the International Standards Organization. It has been converted to ASCII text and then into HTML.
This International Standard has been produced in response to an identified need for a mechanism to allow data structures to be easily moved from one computer system to another, independent of architecture. Data structures required to be interchanged can vary significantly in complexity and size, and a common method to accomplish these interchanges is desirable. It is also desirable that any medium such as a communication line, a magnetic tape, a disk pack, a flexible disk etc., should be able to be used for the physical interchange, and that all information necessary to successfully recreate the structure in the target system should be contained within the information transported on the medium.
To meet these needs this International Standard specifies medium-independent and system-independent file and data record formats for the interchange of information between computer systems. This International Standard is intended for use with physical recorded media as well as with communications media. The contents in the user data structure can be of any internationally recognized character set and coding and are interchanged in a transparent fashion. The intermediate structure through which the informat ion passes is designed for interchange purposes. It can also be used for some forms of general processing and is amenable to direct access methods on high volume, direct access interchange media.
This International Standard is a concrete transfer syntax and encoding standard and provides a tool for the description of files containing user data but does not specify the content or order of user data fields or user data records. It does specify a comprehensive generic form for such records and fields which can accommodate a wide variety of user needs for both simple and complex user data. An application must design its own instance of a conforming interchange file and all conforming files, both data an d data description, will be processable to the field or subfield level by the same software. A user must, of course, complete the interface to their own application system.
The approach used is to define an interchange format into which most information structures and their content can be transformed without loss of information, and from which the original structure and content can be retrieved. The interchange format is suitable both for recording on physical media and transport through a communication system.
The data structures supported by the interchange format are elementary data, vectors, arrays and hierarchies. The file structures that can be transformed into the interchange format include sequential, hierarchical and relational. Network structures are not directly supported and additional pre-processing and post-processing are necessary in this case to preserve logical linkages.
This International Standard is media independent. It assumes, at a minimum, that the supporting transport system can process fixed length octet strings. It requires a computer processing capability to map the user file or database data to the interchange file. This mapping function has to provide the necessary data and structure conversions. The parameters required to define the selection and conversion of these data items and structures into the formats specified by this International Standard are outside the scope of the standard. This International Standard requires the use of a basic character set based on ISO 8859-1 and ISO/IEC 6429 in control fields and permits the use of additional character sets in user data fields. This International Standard provides for three interchange levels from which the users may choose based on the complexity of their data structures. The first interchange level supports multiple fields containing simple, unstructured character strings. The second level supports the first le vel and multiple fields containing structured user data comprising a variety of data types. The third level supports the second level and hierarchical data structures.
The experience of implementing ISO/IEC 8211 for a variety of applications revealed the need for the changes introduced in this version. Many of the changes give ISO/IEC 8211 increased versatility and more effective interchange capabilities. Many other changes were made to improve clarity and user acceptance. Technical changes in the standardized interchange supporting this International Standard and changes in the organizational responsibility for this International Standard have led to other extensions. This version provides the user with an improved interchange tool in keeping with the user's increasing needs and well integrated into the OSI environment.
The retrieval of archived files may require the use of computer systems which are different from the original archiving systems. The operational problems are identical to those involved in the transport of files between computers at different sites and this International Standard provides a facility for this application.
ISO/IEC 8211 is based on ISO 2709 having the same record structure but different data description components. ISO 2709 based systems for file transfer and random file access had been in use since at least 1970 and their use is now extensive. The nomenclature of ISO/IEC 8211 conforms to its predecessor, ISO 2709. Its hierarchical, logical data constructs are files, variable-length records, variable-length fields and subfields. In several programming languages, the equivalent of an ISO/IEC 8211 field is a rec ord and specific applications will transport their records as ISO/IEC 8211 fields with related records aggregated into ISO/IEC 8211 records.
The contents of this standard are organized as follows:
This International Standard specifies an interchange format to facilitate the moving of files or parts of files containing data records between computer systems. The interchange format is not intended as a record format for the indigenous files of any specific system but may be used for this purpose. The standard defines a generalized structure which can be used to transmit, between systems, files or records containing a wide variety of data types and data structures. It specifies the means for the descript ion of the contents of data records but does not specify their application semantics although these semantics can be included as a part of the transmission. The interchange format may also be used to transport individual records, individual data fields or individual subfields with their description.
This International Standard specifies:
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