The routine process of calculating and comparing stored fixity values (e.g., cryptographic hashes or checksums) for a digital object's bitstream over time to detect unintended changes to its stored representation.

Principle

A matching stored fixity value implies the current bitstream equals the recorded bitstream at the time the value was produced; a mismatch implies the bitstream has changed since that recording, triggering investigation or remediation.

Demonstration

Illustrative scenario → An archive schedules nightly checksum verification. Recognition: a scheduled job reports a checksum mismatch for an ingested file. Action: staff retrieve the recorded fixity manifest, compare versions, consult backup copies, and restore or quarantine the affected copy. Consequence: corruption or unauthorized modification is detected early and addressed before broader dissemination.

Misapplication

Mistaken interpretation: treating a matching checksum as proof of authenticity, provenance, or semantic integrity. Error: fixity attests only to byte‑level identity relative to a recorded value; it does not establish origin, intent, or correctness of content.

Consequence

Fixity checking provides a low‑cost, automatable mechanism for detecting bitstream change and supporting integrity monitoring; it cannot by itself prove authenticity, nor can it detect format‑level semantic degradation or authorized in‑place transformations unless those are recorded.

Reversal

For file formats that serialize non‑deterministically (embed timestamps, reorder metadata), raw checksums will vary even for semantically equivalent content; normalization or format-aware hashing is required for meaningful comparison.

Boundary

Clearly within: bitstream integrity verification for preserved files, containers, and storage replicas. Boundary case: compound objects where container metadata changes but payload is stable. Clearly outside: claims about intellectual provenance, semantic accuracy, or format validity that require additional evidence.

Semantic Tension

Integrity Checking ↔ Format Variability — strict bitwise fixity emphasizes exactness, while many preservation operations and formats produce acceptable semantic equivalence without bitwise identity.

Synthesis

Fixity checking is a necessary operational signal for preservation workflows—an objective, automatable detector of change—but it must be combined with provenance, format, and contextual controls to support claims about authenticity or long‑term preservation.