CIP10 - Transaction Metadata label registry

CIP10/README.md

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+---
+CIP: 10
+Title: Transaction Metadata Label Registry
+Authors: Sebastien Guillemot <sebastien@emurgo.io>
+Comments-URI: https://forum.cardano.org/t/cip10-transaction-metadata-label-registry/41746
+Status: Draft
+Type: Standards
+Created: 2020-10-31
+License: CC-BY-4.0
+---
+
+## Abstract
+
+Cardano transaction metadata forces metadata entries to namespace their content using an unsigned integer key. This specification is a registry of which use cases has allocated which number to avoid collisions.
+
+## Terminology
+
+Transaction metadata refers to an optional CBOR object in every transaction since the start of the Shelley era. It is defined as the follow CDDL data structure
+
+```
+transaction_metadatum =
+    { * transaction_metadatum => transaction_metadatum }
+  / [ * transaction_metadatum ]
+  / int
+  / bytes .size (0..64)
+  / text .size (0..64)
+
+transaction_metadatum_label = uint
+
+transaction_metadata =
+  { * transaction_metadatum_label => transaction_metadatum }
+```
+
+## Motivation
+
+The top level of the transaction metadata CBOR object is a mapping of `transaction_metadatum_label` to the actual metadata where the `transaction_metadatum_label` represents an (ideally unique) key for a metadata use case. This allows enables the following:
+
+1) Fast lookup for nodes to query all transactions containing metadata that uses a specific key
+2) Allows a single transaction to include multiple metadata entries for different standards
+
+Creating a registry for `transaction_metadatum_label` values has the following benefit:
+
+1) It makes it easy for developers to know which `transaction_metadatum_label` to use to query their node if looking for transactions that use a standard
+2) It makes it easy to avoid collisions with other standards that use transaction metadata
+
+## Specification
+
+These are the registered `transaction_metadatum_label` values
+
+transaction_metadatum_label | description
+----------------------------|-----------------------
+0 - 15                      | reserved*
+65536 - 131071              | reserved - private use
+
+\* It's best to avoid using `0` or any a similar number like `1` that other people are very likely to use. Prefer instead to generate a random number
+
+## Copyright
+
+This CIP is licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/legalcode)