The chain proves it.
The network keeps it useful.
Think of a shared specialist library. The blockchain—the public ledger—orders transactions. The overlay—the specialist network—uses a published filter to choose relevant records, and separately run services keep copies. The app shows them. A Merkle proof is a cryptographic receipt, not a backup: it checks a record you received but cannot restore anything nobody saved.
01 / The shift
A blockchain is a truth machine.
It is not your app’s filing cabinet.
At scale, your birdwatching app should not search the history of world commerce to find Canada goose sightings. People who care about bird sightings should exchange those transactions, keep the records they value, and retain the evidence that lets anyone verify them.
Specific
Each topic defines exactly which outputs belong.
Shared
Independent hosts replicate what they choose to support.
Proven
SPV evidence validates records without replaying the whole chain.
02 / The anatomy
Think neighborhood library, not global warehouse.
The blockchain supplies shared ordering and settlement. An overlay behaves like a group of specialized librarians: each follows the same cataloguing rule, keeps the material it has agreed to preserve, and can show where an item came from.
- PublishA user creates a transaction.01
- AdmitTopic rules decide whether outputs belong.02
- ShareInterested hosts exchange them directly.03
- ProveEvidence anchors them to valid history.04
- FindLookup services answer useful questions.05
What belongs where?
Blockchain
Global ordering, transaction validity, double-spend prevention, and block commitment.
Shared consensusOverlay
Application admission rules, chosen records, state transitions, replication, and useful indexes.
Shared interestApplication
Experience, permissions, workflows, identity choices, and the questions people need answered.
User contextThe boundaries matter: an overlay does not replace mining, and mining does not promise that every application byte will remain conveniently retrievable forever.
03 / The coordination layer
Four jobs.
Four memorable handles.
These names are coordination conventions, not magic availability. They work when people operate compatible services and actually retain what a topic needs.
Who hosts this topic?
Service Host Interconnect Protocol advertisements let services discover hosts interested in a topic. The overlay stack can then propagate relevant transactions among them.
Read BRC-88Who can answer this query?
Service Lookup Availability Protocol advertisements expose lookup services and the questions they know how to answer.
Read BRC-88How do I catch up?
Graph-aware synchronization finds outputs a peer is missing, walks unknown transaction ancestry, validates the graph, and brings a new or returning host into useful alignment.
See the current packageDo I have the confirmed set?
Block-Aligned Sparse Merkle trees anchor admitted transaction positions to a block so peers can compare confirmed topic state and efficiently locate differences.
Read BRC-13604 / Proof travels with the record
Trust less.
Verify the piece.
An overlay answer is useful because the recipient can validate the transaction and its evidence—not because the server asks to be believed.
BEEF can package a transaction with the ancestry evidence needed for validation.
BUMP compactly represents Merkle paths.
SPV lets a recipient check inclusion and transaction history without mirroring every unrelated transaction.
05 / A real recovery question
There is a goose
inside this transaction.
A real BirdSV transaction contains structured sighting data and an image. It was mined. But what would make that sighting easy for someone else to recover years after the original site disappeared?
The proof can authenticate retained bytes. It cannot summon an image or schema that no accessible archive still holds.
Name the topic
Publish a stable, versioned definition for what counts as a BirdSV sighting.
Keep full artifacts
Retain raw transactions, content, validation ancestry, Merkle proofs, and the headers needed to check them.
Multiply custodians
Run independent hosts and test that a newcomer can rebuild the useful index without the original app.
Keep these distinctions
06 / Choose your next move