Data Repositories

A data repository is a collection of data published by a single user. Repositories are self-authenticating data structures, meaning each update is signed and can be verified by anyone.

They are described in more depth in the Repository specification.

Data Layout

The content of a repository is laid out in a Merkle Search Tree (MST) which reduces the state to a single root hash. It can be visualized as the following layout:

┌────────────────┐
│     Commit     │  (Signed Root)
└───────┬────────┘
        ↓
┌────────────────┐
│   Tree Nodes   │
└───────┬────────┘
        ↓
┌────────────────┐
│     Record     │
└────────────────┘

Every node is an IPLD object (dag-cbor) which is referenced by a CID hash. The arrows in the diagram above represent a CID reference.

This layout is reflected in the AT URIs:

Root       | at://alice.com
Collection | at://alice.com/app.bsky.feed.post
Record     | at://alice.com/app.bsky.feed.post/1234

A “commit” to a data repository is simply a keypair signature over a Root node’s CID. Each mutation to the repository produces a new Commit node.

Identifier Types

Multiple types of identifiers are used within a Personal Data Repository.