Editing Collection (section)

== Architecture ==

=== Structure and Addressing ===
Within a collection, individual records are identified by a unique key, known as a [[record key (rkey)]]. The combination of a user's [[Decentralized Identifier (DID)]] or [[handle]], a collection NSID, and a record key forms an [[AT URI]] that uniquely identifies any record within the network. For example:<syntaxhighlight lang="text">
at://did:plc:abcdef123456/app.bsky.feed.post/3jui7kdo2ck

</syntaxhighlight>This URI points to a specific post (with key <code>3jui7kdo2ck</code> in the <code>app.bsky.feed.post</code> collection of the user with the specified DID.

Record keys are typically generated as [[Timestamp Identifier (TID)|Timestamp Identifiers (TID)]] which embed creation time information, though other formats are supported for specific use cases. The key format requirements are defined by the [[lexicon]] for each collection's record type.

=== Indexing and Querying ===
Collections are an indispensible part of the network's indexing infrastructure. [[Relay|Relays]] and [[AppView|AppViews]] use collection NSIDs to filter and process specific types of records from the [[firehose]] of network activity. This allows them to build specialized indices and provide efficient query capabilities for particular content types. For example, an AppView might specifically index the <code>app.bsky.feed.post</code> and <code>app.bsky.feed.like</code> collections to build a timeline view, while ignoring other collections that aren't relevant to that particular feature.

=== Data Portability ===
The collection-based organization of repositories facilitate data portability within the AT Protocol. When users migrate between [[Personal Data Server (PDS)|Personal Data Servers (PDSes)]], their entire repository, including all collections and records, can be exported and imported as a unit, preserving the organizational structure and relationships between records.

=== Security and Access Control ===
Collections provide a natural boundary for access control policies. While most collections in the current AT Protocol implementation contain public records, the architecture supports future extensions for collection-level privacy settings. For example, future implementations might include private or group-restricted collections that are only visible to specified users or groups, enabling private messaging and selective sharing features.

=== Repository Implementation ===
In the underlying [[data repository]] implementation, collections are represented as paths within the [[Merkle Search Tree (MST)]] data structure. The MST organizes records hierarchically, with collection NSIDs forming part of the peath for each record.

When a PDS receives a request to create or update a [[record]], it validates that the record's <code>$typr</code> field matches the collection NSID where it's being stored to ensure type consistency within collections and prevent misplaced records.

[[Category:Data structures]]