The assignment or occurrence of the same identifier (URI, DOI, ISBN, local accession number, etc.) referring to more than one distinct resource, manifestation, or entity, causing ambiguity in resolution, linking, or metadata association.

Principle

Identifiers must be unique within their resolution scope and accompanied by namespace and versioning rules; collisions arise from inadequate namespace governance, identifier reuse, or inconsistent resolution policies and create failures in authoritative resolution or linking.

Demonstration

Illustrative scenario — Situation: A DOI mistakenly minted for two different articles. Recognition: a DOI resolver returns one article while metadata for citations refers to another. Action: notify registration agency, deprecate one DOI or assign a new DOI, add redirects and provenance notes to affected records. Consequence: restored resolvability and corrected citation targets after coordinated remediation.

Misapplication

Assuming a locally unique identifier (e.g., an internal accession number) is globally resolvable. This conflates scope: identifiers unique only within a local namespace can collide when shared externally without namespace qualification.

Consequence

Identifier collisions cause broken or ambiguous links, incorrect aggregation of metadata, citation errors, and interoperability failures; causally, they break the invariant that an identifier deterministically resolves to a single referent under the system's resolution rules.

Reversal

Some controlled systems intentionally reuse identifiers (e.g., recycled local accession numbers in a closed archive) or map multiple physical manifestations to a single conceptual identifier; in such cases collision is either managed by scope or by explicit versioning and should not be treated as an error if governed by policy.

Boundary

Clearly within: persistent identifiers and resolvable URIs whose namespace policy intends uniqueness. Boundary case: identical token strings used in different namespaces (ISBN vs internal barcode) that are non‑colliding when namespace qualified. Clearly outside: conceptual equivalence across different identifiers intentionally representing the same conceptual object (e.g., a work-level identifier linking several edition identifiers).

Semantic Tension

Global Uniqueness ↔ Decentralized Minting — enforcing global uniqueness simplifies resolution but constrains distributed authority; decentralized minting supports local control but requires robust namespace and provenance mechanisms to avoid collisions.

Synthesis

An identifier collision exposes insufficient namespace governance or versioning practice: durable interoperability requires clear scope, namespace qualification, versioning, and policies for deprecation and redirection rather than ad hoc identifier reuse.