WrittenOnce

WrittenOnce is a concept in information management describing data that is written in a single, final state and subsequently maintained in an immutable form. The term is often used in contrast with writable systems and with the broader category of write-once memory (WOM). Unlike hardware-only approaches, writtenOnce emphasizes policy, cryptography, and provenance to ensure immutability across software layers and storage ecosystems.

Implementation typically relies on append-only data structures, cryptographic hashes, time-stamped digital signatures, and immutable storage back-ends. Some approaches employ distributed ledgers or blockchain to provide tamper-evident provenance, while others use write-once or WORM-capable storage devices combined with strict access controls and retention policies. The goal is to make the original content verifiable and resistant to undetected modification.

Common use cases include regulatory archival, legal documents, research data, financial logs, and compliance audits, where integrity and traceability of the original content are critical. Governance considerations cover key management, access controls, retention schedules, and the risk of irreversible errors; once content is written in a truly immutable manner, it cannot be altered or deleted by design. Therefore, data quality at the point of writing and well-defined lifecycle processes are essential.

Challenges include privacy concerns, potential over-retention, and operational overhead. In practice, systems may implement soft immutability for a defined period or provide controlled mechanisms for reversal under strict policy or oversight, but the core principle remains: content that is writtenOnce should remain unchanged after publication.

See also: WORM, blockchain, immutable ledger, data provenance, digital signatures.