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ISO/IEC 8211 Data Descriptive File (DDF)

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ISO/IEC 8211:1994, Information technology - Specification for a data descriptive file for information interchange.
Description

ISO/IEC 8211 specifies an interchange format to facilitate the moving of files or parts of files containing data records between computer systems. The objective of the standard was to support interchange of data structures varying significantly in complexity and size. Another objective was 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." A third was "that all information necessary to successfully recreate the structure in the target system should be contained within the information transported on the medium."

The introduction to the standard lists the components specified by the standard:

  • media-independent file and data record descriptions for information interchange;
  • the description of data elements, vectors, arrays and hierarchies containing bit strings, character strings and numeric forms;
  • a data descriptive file composed of a data descriptive record and companion data records that enable interchange to occur with minimal specific external description;
  • the data descriptive record that describes the characteristics of each data field within the companion data records;
  • three levels of complexity of file and record structure;
  • FTAM unstructured and structured document types

Its data constructs are files, variable-length records, variable-length fields and subfields. This nomenclature and record structure is based on a generalization of the ISO 2709 record structure used for MARC (MAchine-Readable Cataloging) records. The data structures supported are elementary data, vectors, arrays, and hierarchies.

Production phase Designed for generic, system-independent interchange of datasets. A particular application of the format may be appropriate as an archival format.
Relationship to other formats
    Used by SDTS, Spatial Data Transfer Standard

Local use Explanation of format description terms

LC experience or existing holdings None.
LC preference None expressed. The Library of Congress does not currently collect datasets that might originate in this format.

Sustainability factors Explanation of format description terms

Disclosure Fully disclosed international (ISO/IEC) standard.
    Documentation ISO/IEC 8211:1994, Information technology - Specification for a data descriptive file for information interchange.
Adoption Although generic in applicability, adoption seems to the compilers of this resource to be primarily in the geospatial domain. The Spatial Data Transfer Standard (SDTS) is based on this format. Comments welcome.
    Licensing and patents No known license or patent concerns for generation and use of the format. Comments welcome.
Transparency The degree to which the data in an ISO/IEC 8211 file can be read with simple tools (e.g. text editors) depends on the particular data definitions employed. In general, formats storing numeric data in binary form require software capable of manipulating or transforming binary numbers.
Self-documentation Self-documentation is a primary objective of the specification.
External dependencies Requires software capable of interpreting data in this format. A few software tools claiming ISO 8211 reading support can be located. However the compilers of this resource are not aware of a well supported tool or software library for interpreting and transforming data in this format that is not proprietary.
Technical protection considerations None.

Quality and functionality factors Explanation of format description terms

Dataset
Normal functionality This format has extensive capabilities for declaring and defining data types for numeric and character data fields and for assembling data into structures such as rectangular and multidimensional arrays, lists, tables and clusters. See Notes below.
Support for software interfaces (APIs, etc.) This standard does not define an API or support a well known API. Although a few software tools with ISO 8211 reading support can be located, the compilers of this resource are not aware of a currently (as of February 2011) supported software library to create, manipulate, and use data in this format. The record structure is designed to facilitate convenient access to particular fields and subfields without parsing the entire record.
Data documentation (quality, provenance, etc.) This standard defines a generic serialization mechanism for defining data structure and recording data according to that structure. An application of the standard might define a structure to record information relating to data quality or provenance, but the standard has no direct support.
Beyond normal functionality Unlike dataset formats with prescribed lists of supported data types and structures, this format offers, in theory, a high level of flexibility to customize dataset resources.

File type signifiers Explanation of format description terms

Tag Value Note
Filename extension .ddf
 

Notes Explanation of format description terms

General

The informative Annex B of the 1994 edition of the standard has a useful description (in the paragraph below) making it clear that ISO/IEC 8211 is intended as a generic interchange format to be used as a serialization for data structures within a user domain and with semantic details for those data structures documented through another layer of specification.

"This International Standard specifies a method for the description of user data fields contained in interchange files and a general method for combining user data fields into user data records. Within the specified methods a user must specify the details for a specific application. An interchange file set may contain several files and each file may have its own requirements for record content and order as well as the content and order of fields within records. The user is responsible for this design and must prepare, validate and maintain the specification. This International Standard specifies the occurrence of the data description as it appears in the octet string of the DDR which is intended for machine processing and not for human readability."

A data descriptive file (DDF) consists of a sequence of logical records. A logical record has a Leader followed by a Directory and a Field Area. The Leader contains the parameters necessary to read records, and in particular to disaggregate the Directory. The Directory contains the parameters necessary to identify and locate each field in the Field Area. The first record in a DDF is the Data Descriptive Record (DDR). The Field Area of the DDR holds the information necessary to decode the data in the Field Areas of the Data Records (DRs) that follow.

ISO/IEC 8211 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 level and multiple fields containing structured user data comprising a variety of data types. The third level supports the second level and hierarchical data structures.

History Based on ISO 2709, using the same nomenclature and record structure, but with different data description components. Whereas values in ISO 2709 are alphanumeric strings, ISO/IEC 8211 also supports a variety of representations for numbers, including integer, real, binary, floating point, etc.

Format specifications Explanation of format description terms


Useful references

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Last Updated: 01/20/2014