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In 2005, an International Standards Organization (ISO) committee released PDF/A, the first independent, multinational standard for digital archives. PDF/A is based on a subset of the Portable Document Format (PDF) developed by Adobe Systems Incorporated (Adobe).
Defining Requirements for Digital Archiving
Until the 1990s, many organizations manually stored fixed content on centralized, hard-copy archives; typewriters, microfiche readers, magnetic tape, file cabinets, and warehouses were tools of the trade. Then electronic document creation and archiving began to take hold as a standard business practice. As companies attempted to standardize their digital archiving processes based on existing paper-based practices, the following common requirements emerged.
Document Authenticity
Organizations must be able to establish the authenticity of a document's contents and origin, including assertions about creator, sender, and time of creation or modification. These legitimizing details must be secure and available upon request.
Methods for establishing authenticity include registration of unique document identifiers and the inclusion of metadata. Hashing and digital time-stamping visibly authenticate the existence of a document; the latter method does so at a specific time. Encapsulation and encryption can also store a hidden digital "watermark," which can be detected only by appropriate software, and used primarily for protection against unauthorized copying. Digital signatures establish authorship and cite contributors.
Process Reliability
Organizations must implement a system that ensures content authenticity and accurately documents the transaction or information to which it attests. To meet this requirement, archiving processes must directly and automatically capture content from the system of origin.
Methods for ensuring process reliability for authored content include direct archive-export functionality, which is built directly into the authoring application. For computer-generated content, process reliability can be maintained through an automated archiving system that detects and captures output from line of business systems.
Content Security
Documents must be protected from unauthorized alterations. For digital archives, document protection includes being rights managed, with control over write, edit, annotation, print, and save access.
Authorized annotations must maintain an obvious and consistent visual appearance to distinguish them from the original encapsulated content. Annotations must be monitored and tracked, providing date, time, and author.
Persistent Accessibility
Persistent accessibility is as much a goal as a requirement of archiving, which demands that documents remain consistently available and visually uniform over time, independent of viewing circumstances. In environments where accessibility cannot be guaranteed at the file level, organizations sometimes archive document viewing software, operating systems, and hardware, in addition to documents, to ensure that documents can be accessed.
To ensure that accessibility can be preserved, the archive format must support self-describing data that can fully determine composition. Document appearance and composition must be fully encapsulated and independent of any particular application or operating system. This ensures that valid applications can consistently render a document, regardless of operating system and without additional resources (external font files, linked graphics, etc.).
Lifecycle Management
Digital archives must be capable of content management and lifecycle management at the document level. Organizations must be able to define individual document objects, then assign attributes and apply policies based on those attributes, enabling content management and lifecycle management functions to be executed. Long-term lifecycle management includes scheduled creation, transfer, replication, and destruction.
Lifecycle management can be executed according to internal or external metadata. Internally referenced metadata is encapsulated within the file itself. Externally referenced metadata (e.g., XML) is responsible for identifying corresponding documents that must be managed, as well as providing relevant instructions to a lifecycle management platform. Ideally, a digital archive format supports internal and external metadata.
PDF: Adobe's Answer to Digital Archive Requirements
Adobe developed the Portable Document Format specifically to meet the requirements of digital archiving. PDF evolved from Adobe's PostScript page description language. PostScript introduced a format that enabled desktop printers to render complex text and graphics images according to self-contained reference information. Considering the strategic advantages of an encapsulated print language, Adobe began developing a similar technology to provide the same encapsulated consistency for printing, viewing, and communicating documents electronically.
Open Standards Specification
Publicly available since 1993, PDF only recently earned recognition as an open-specification solution for archiving. This is partly due to a public misconception that PDF is a proprietary Adobe format.
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