Sustainability of Digital Formats: Planning for Library of Congress Collections

Archive eXchange Format (known as AXF), as defined by AXF.io, "is an open-standard object-container for file-based assets and their associated metadata." The standard ISO/IEC 12034-1:2017 Information Technology - Archive eXchange Format (AXF) describes AXF as "an open format that supports interoperability among disparate data storage systems and ensures long-term availability of data, no matter how storage or file system technologies evolve. AXF inherently supports interoperability between existing, discrete storage systems, irrespective of the operating and file systems used, and also future-proofs digital storage by abstracting the underlying technology so that content remains available across generations of technology development."

Craig Johnston, in the article, SMPTE Developing Archive Standard, 2011, describes archive standards and AXF, quoted Merrill Weiss, the chair of the Society of Motion Picture and Television Engineers (SMPTE)'s Working Group on AXF and president of Merrill Weiss Group - LLC, describes AXF as "a wrapper that can handle not just media files but any type of file, including text files, XML files, Excel spreadsheets, Word documents, executables, you name it."

AXF Format Characteristics:

Brian Campanotti, of Front Porch Digital, describes AXF in the presentation, Archive eXchange Format AXF, 2012, as "like an advanced ZIP which encapsulates any number of files, metadata and a ubiquitous file system." He also lists the following characteristics of AXF:

• Unlimited storage support.
• Resilience to media damage and corruption.
• Support for media with and without a file system.
• Support for any file system or operating system.
• Self-describing objects and self-describing media.
• Object versioning and collection support.
• Support for all file types - not just media files.
• Streaming and file-based asset transport and delivery.

According to AXF.io's FAQs page, AXF "is the worlds only published open-standard focused on transport, long-term access, protection and preservation of file-based asset collections regardless of their origin."

AXF.io's Technology page provides an Introduction and Overview of the AXF format standard, stating the standard "is based on an embedded file system...Each AXF Object is a fully self-contained, encapsulated collection of files, metadata and any other ancillary information which adds relevancy or value to its contents."

AXF Internal Structures:

The AXF Standard describes AXF Objects as being comprised of four main components (descriptions of components as per AXF.io, AXF Object Components):

• Object Header:
  • Structure containing descriptive XML metadata, describes actual content of AXF Object, such as Unique Identifier, creation date.
• Metadata Container:
  • Optional AXF Generic Metadata packages.
  • "Self-contained, open metadata containers for applications to include AXF Object-specific metadata."
  • Can be: Structured/Unstructured, Open/Vendor Specific, Binary/XML.
  • No constraints/standards for this metadata.
• File Payload:
  • File Payload Start marks start of file payload.
  • File Payload consists of zero or more File Data + File Padding + File Footer triplets, actual byte data of the files stored in AXF Object container.
  • File Payload Stop marks the end of file payload.
• Object Footer:
  • Essentially repeat of Object header information with some additional creation information, such as checksums, block positions, file permissions.
  • Fundamental to resiliency of AXF.

As stated on AXF.io's AXF Object Components, "Each AXF Object component is itself encapsulated in a Binary Structure Container envelope which provides structure identification, index structure checksums, classification information, media/mime types, etc...The Binary Structure Container is a simple binary envelop which wraps/contains payload information...The Binary Structure Container allows the application to comprehend its contents allowing it to be stored, validated, tracked and reliably recovered regardless of its nature or origin."

Other AXF Significant Structures:

According to the AXF standard, "other significant structures in the AXF protocol are AXF Medium Identifiers and AXF Object Indices. AXF Medium Identifiers are used on media to indicate formatting of the media according to the AXF protocol and to provide unique identification of the media. AXF Object Indices are optional compilations of the information in all Object Footers preceding each AXF Object Index on a medium, providing a single structure from which it is possible to obtain complete information on the contents of the preceding portion of a medium."

Uses of AXF:

As AXF.io FAQs page states, "Anyone who works with any type of file based content and needs to store, transfer, protect, preserve or access their content across various technologies can benefit from AXF. From people and companies that work within the entertainment industry who need a long-term solution for storing large volumes of big media files down to the person who just needs to transfer or store a few files with focus on future accessibility."

According to S. Merrill Weiss in the article, Archive Exchange Format (AXF) Explained, February 2014, "AXF ensures the long-term availability and utility of digital content as both storage and file system technologies evolve. AXF offers a mechanism by which users can store an unlimited number and variety of files within a single wrapper. Independent of any particular archive system, the resulting AXF Object can be stored on any kind of medium and migrated easily from one media type or generation to another. Because AXF Objects are both self-contained and self-describing, assets are formatted in a way that makes them readily retrievable over time."

Open and non-proprietary. As stated on Oracle.com's Glossary, "The Archive Exchange Format (AXF), or AXF Media Format, is based on a file and storage media agnostic encapsulation approach which abstracts the underlying file system, operating system, and storage technology making the format truly open and non-proprietary."

AXF is a published International Standard (SMPTE and ISO/IEC).

ISO/IEC 12034-1:2017 | Information technology - Archive eXchange Format (AXF) - Part 1: Structure and semantics. Available for purchase. See (https://www.iso.org/standard/73525.html).

ST 2034-1:2017 - SMPTE Standard - Archive eXchange Format (AXF) - Part 1: Structure & Semantics. See (https://ieeexplore.ieee.org/document/7879152).

AXF Community Home. See (https://axf.io/index.html).

As described in the AXF.io's History, AXF has been successfully deployed across various storage technologies (flash, disk, tape, optical, and Cloud) and a multitude of file-based asset types in many industries touching various applications and environments.

According to Summer McIennan, in the news article, SMPTE Archive eXchange Format (AXF) Standard Proves Immediate Success in Real-World Adoption and Implementation, 2016, AXF has been successfully adopted and executed, smoothly supporting the transparent and independent exchange of complex file-based assets and metadata between storage management applications from different vendors.

Comments welcome.

According to AXF.io's FAQs page, "there is a small one-time administrative fee to download the AXF standard document unless you or your organization already have access to a SMPTE or ISO standards subscription. Once you have acquired the standard document, AXF is available unencumbered which means you are free to develop, use and access AXF technologies in perpetuity as there are no ongoing license or use fees."

Comments welcome.

AXF structural elements themselves are documents coded in XML, a format that is both human-readable and machine-readable.

Comments welcome.

As stated on AXF.io, "AXF allows you to bundle files any amount of metadata (descriptive, technical, proprietary, etc.) into an immutable, self-describing preservation package while maintaining your ability to dynamically interact with any of the assets contained inside an object."

Accessibility Features

As noted on the AXF homepage, "as long-term preservation and accessibility is key, AXF includes many foundational resilience features such as redundant index structures, file and metadata signatures, file-footers which replicate core file-data and more." Although "accessibility" in this quote seems to refer to overall access to content rather than digital accessibility, the sentiment is still relevant. Because AXF is a highly defined self-contained and self-describing format, it has the capacity for integrating accessibility support for contained content through captions, subtitles, timed text and more depending on implementation. Comments welcome.

None. As stated on AXF.io, "AXF was designed to support any scale and mix of storage technology (including what you already have), operating-systems and file-systems whether they are deployed On-prem or in the Cloud."

Comments welcome.

The AXF Standard Preview states, "AXF also carries key preservation information, such as provenance, fixity, and the like - all key to ensuring long-term robustness and recoverability...AXF offers resilience to data corruption and loss. AXF Object Indices, repeated identifier instances, and cryptographic hash checksums on both contents and AXF Objects allow for data corruption to be identified and mitigated."

Comments welcome.

Little or no information found on AXF's compression support. AXF.io shows support for OAIS standards for preservation, but little information found on compression types. AXF.io describes AXF as Preservation Focused, "AXF will not impede workflow as it was designed from the ground up to support any usage patterns in any environment while still delivering true OAIS-Standard preservation benefits."

Comments welcome.

Some support. As stated in the article, Archive eXchange Format, "As an entirely self-contained and self-describing format, AXF supports large-scale archive systems as well as simple standalone applications, facilitating encapsulation or wrapping, long term protection and content transport between systems from different vendors who also conform to the AXF specification. Fundamental features such as per-file checksums, per-structure checksums and easy replication across any storage technology help to ensure compatibility with evolving technology and a secure future."

Comments welcome.

None.

Comments welcome.

Development of AXF started in 2006. According to AXF.io, "thought leaders and industry experts from Front Porch Digital, Masstech and SGL meet in Las Vegas to discuss the industry need for a standard to store, protect and preserve the immense (and valuable) data-sets in Media and Entertainment." In 2008, they officially became a working committee under SMPTE. AXF's first public release was in 2011. AXF became an SMPTE standard in 2014 and an ISO/IEC standard in 2017.