contentidentifiers

Content identifiers are values assigned to digital content that identify the item by its data rather than by a storage location. In content-addressable systems, the identifier often takes the form of a cryptographic hash of the content, sometimes with additional structure to describe how the hash was produced and what type of content is being identified. The key properties of content identifiers are immutability (changing the content yields a different identifier), data integrity (the identifier can be recomputed to verify content has not been altered), and facilitation of deduplication (identical content yields the same identifier across storage nodes).

A prominent example is the Content Identifier (CID) used in IPFS and related projects. A CID is a self-describing pointer that encodes the version, the data format (codec), and the multihash of the content. CIDs support multiple hashing algorithms and encodings, enabling flexible and extensible representation. In IPFS, CIDs allow files and objects to be retrieved from any node that stores the data, rather than from a single fixed server, supporting resilient and decentralized networks.

Advantages of content identifiers include improved data integrity verification, easier provenance tracking, and more efficient caching and deduplication. They also enable offline or offline-to-online retrieval scenarios, since the identifier remains meaningful regardless of where the data is stored.

Limitations involve the need for tooling to generate and resolve identifiers, potential overhead from hashing large objects, and the requirement that the content remains accessible under the same identifier for long-term validity. Content identifiers contrast with location-based identifiers like URLs, which depend on a specific server location.