Sustainability of Digital Formats: Planning for Library of Congress Collections

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ZIP File Format, Version 6.2.0 (PKWARE)

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name ZIP File Format, Version 6.2.0 (PKWARE)
Description

The ZIP format is designed for cross-platform data exchange and efficient data storage for a set of related files. ZIP_PK is a de facto industry standard, developed, maintained, and openly documented by PKWARE. The original version of the format was developed by Phil Katz (hence the "PK" in PKWARE). Like the earlier versions of ZIP_PK, ZIP_6_0_2, published in April 2004, combines data compression, file management, and data encryption within a portable archive format. A ZIP file is a package containing one or more files, usually compressed and sometimes encrypted. The basic structure consists of a sequence of chunks comprising a "local file header" followed by the file data (after compression and/or encryption) followed by a chunk known as the "central directory," which lists the files in the package along with key metadata to support their extraction, decryption, etc. Of the extensions to ZIP since its introduction that are most significant for open, interoperable functionality, version 6.2.0 supports:

  • the widely used Deflate data compression algorithm;
  • support for large files, raising the 65535 limit on the number of files in a ZIP file and allowing file sizes beyond the previous 4 gigabyte limit.

Of the functional extensions other than new compression methods and enhanced encryption, version 6.2.0 lacks one extension that has proved important for worldwide adoption. It does not support the use of UNICODE in filenames. See ZIP_PK for detail on other chronological versions.

ZIP_6_2_0 has been incorporated as the package or container for digital formats that represent a single document or other logical unit but comprise multiple files. See Notes below for details on use by OOXML (Office Open XML) and ODF (Open Document Format).

Production phase May be used at any lifecycle phase for bundling/packaging files together for exchange, storage, or distribution. In particular, XML-based office productivity formats OOXML and ODF have used constrained forms of this version of the ZIP format to package the component files of their XML-based formats for editable office documents.
Relationship to other formats
    Subtype of ZIP_PK, ZIP File Format (PKWARE)
    Has subtype OPC/OOXML_2012, Open Packaging Conventions (Office Open XML), ISO 29500-2:2008-2012
    Has subtype ZIP_6_2_0 is used as the basis for storing office documents in versions 1.0 through 1.2 of Office Document Format (ODF), standardized as ISO 26300 (not described at this web site at this time).

Local use Explanation of format description terms

LC experience or existing holdings See ZIP_PK.
LC preference See ZIP_PK.

Sustainability factors Explanation of format description terms

Disclosure The ZIP_PK format has been developed and maintained by PKWARE, Inc. since 1998. The format specification is proprietary, but the most recent version has always been openly disclosed as the .ZIP Application Note with a file name of APPNOTE.TXT.
    Documentation

Version 6.2.0 of ZIP is documented in APPNOTE.TXT, Version 6.2.0 (April 2004).

Adoption See ZIP_PK.
    Licensing and patents See ZIP_PK.
Transparency See ZIP_PK.
Self-documentation See ZIP_PK.
External dependencies See ZIP_PK.
Technical protection considerations See ZIP_PK.

Quality and functionality factors Explanation of format description terms

Other
Bundling/compression Separate functionality factors for comparing formats that are used to bundle and or compress files have not been developed. From the perspective of digital preservation, consideration of the sustainability factors above is more important than the degree of compression.
Beyond normal See ZIP_PK.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension zip
ZIP
Other extensions are used for particular applications that use the ZIP format as a container, for example, OOXML specifies .docx, .xslx, .pptx as the file extension, depending on the document type.
Internet Media Type application/zip
Other Internet Media Types are used for particular applications that use the ZIP format as a container, for example, ODF uses application/vnd.oasis.opendocument.txt for textual doxuments. See also ZIP_PK.
File signature See related format.  See ZIP_PK.

Notes Explanation of format description terms

General

ZIP_6_2_0 has been incorporated as the package or container for several digital formats that represent a single document or other logical unit but comprise multiple files. These include:

  • Office Open XML (OOXML, standardized as ECMA 376 and ISO/IEC 29500)
    The Open Packaging Conventions (OPC, Part 2 of ISO/IEC 29500, OOXML) are based on version 6.2.0. Compression is restricted to DEFLATE; digital signatures are not supported. Details on the use of ZIP in OPC are in section 10 and Annex C of ISO/IEC 29500-2:2012.
  • Office Document Format (ODF), standardized as ISO/IEC 26300
    Version 1.2 of ODF (Open Document Format for Office Applications) from OASIS incorporates version 6.2.0. The only compression algorithm allowed is DEFLATE (RFC 1951). ODF defines its own encryption mechanism. Version 1.0 of ODF (as published as ISO/IEC 26300:2006) referred to the APPNOTE.TXT version dated 1997-03-11 from Info-ZIP, because no appropriate version was made available publicly by PKWARE at the time because the version 6.2.0 referred to by the original ODF specification from OASIS had been superseded. Now that PKWARE maintains an archive of documentation to facilitate persistent references, Version 1.2 of ODF again refers to version 6.2.0.
History  

Format specifications Explanation of format description terms


Useful references

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Last Updated: 02/27/2017