CIP-0068: Add SFT Semi-fungible token support

CIP-0068/README.md

@@ -147,7 +147,7 @@ datum = #6.121([metadata, 1, extra]) ; version 1
 ```
 Example datum as JSON:
 ```json
-{"constructor" : 0, "fields": [{"map": [{"k": "6E616D65", "v": "5370616365427564"}, {"k": "696D616765", "v": "697066733A2F2F74657374"}]}, {"int": 1}]}
+{"constructor" : 0, "fields": [{"map": [{"k": {"bytes": "6E616D65"}, "v": {"bytes": "5370616365427564"}}, {"k": {"bytes": "696D616765"}, "v": {"bytes": "697066733A2F2F74657374"}}]}, {"int": 1}]}
 ```
 
 ### Retrieve metadata as 3rd party
@@ -225,7 +225,7 @@ datum = #6.121([metadata, 1, extra]) ; version 1
 ```
 Example datum as JSON:
 ```json
-{"constructor" : 0, "fields": [{"map": [{"k": "6E616D65", "v": "5370616365427564"}, {"k": "6465736372697074696F6E", "v": "54686973206973206D79207465737420746F6B656E"}]}, {"int": 1}]}
+{"constructor" : 0, "fields": [{"map": [{"k": {"bytes": "6E616D65"}, "v": {"bytes": "5370616365427564"}}, {"k": {"bytes": "6465736372697074696F6E"}, "v": {"bytes": "54686973206973206D79207465737420746F6B656E"}}]}, {"int": 1}]}
 ```
 
 ### Retrieve metadata as 3rd party
@@ -246,6 +246,92 @@ We want to bring the metadata of the FT `d5e6bf0500378d4f0da4e8dde6becec7621cd8c
 3. Reference the output in the transaction. (off-chain)
 4. Verify validity of datum of the referenced output by checking if policy ID of `reference NFT` and `user token` and their asset names without the `asset_name_label` prefix match. (on-chain)
 
+## 444 SFT Standard
+
+The third introduced standard is the `444` Semi-FT standard with the registered `asset_name_label` prefix value
+
+| asset_name_label            | class        | description                                                          |
+| --------------------------- | ------------ | -------------------------------------------------------------------- |
+| 444                         | SFT          | SFT hold by the user's wallet making use of the union of CIP-0025 inner structure AND the Cardano foundation off-chain registry inner structure |
+
+Semi-Fungible tokens don't fit cleanly into the other two FT/NFT classes of tokens and thus need their own standard. An example of a SFT would be a fractionalized NFT. The single reference NFT `(100)` represents the NFT itself, and the many `(444)` tokens represent the fractionalized shares. Minting 100 tokens and setting decimals to 2 would represent a single NFT that is split into 100 fractions.
+
+### Class
+
+The `user token` is an SFT (semi-fungible token).
+
+### Pattern
+
+The `user token` and `reference NFT` **must** have an identical name, preceded by the `asset_name_label` prefix.
+
+Example:\
+`user token`: `(444)Test123`\
+`reference NFT`: `(100)Test123`
+
+### Metadata
+
+This is a low-level representation of the metadata, following closely the structure of CIP-0025 combined with the Cardano foundation off-chain metadata registry. All UTF-8 encoded keys and values need to be converted into their respective byte's representation when creating the datum on-chain.
+
+```
+files_details = 
+  {
+    ? name : bounded_bytes, ; UTF-8
+    mediaType : bounded_bytes, ; UTF-8
+    src : bounded_bytes ; UTF-8
+    ; ... Additional properties are allowed
+  }
+
+metadata = 
+  {
+    name : bounded_bytes, ; UTF-8
+    description : bounded_bytes, ; UTF-8
+    image : bounded_bytes, ; UTF-8
+    ? mediaType : bounded_bytes, ; UTF-8
+    ? ticker: bounded_bytes, ; UTF-8
+    ? url: bounded_bytes, ; UTF-8
+    ? logo: uri,
+    ? decimals: int,
+    ? files : [* files_details]
+    ; ... Additional properties are allowed
+  }
+
+; A URI as a UTF-8 encoded bytestring.
+; The URI scheme must be one of `https`, `ipfs` or `data`
+; Do not encode plain file payloads as URI.
+; 'logo' does not follow the explanation of the token-registry, it needs to be a valid URI and not a plain bytestring.
+; Only use the following media types: `image/png`, `image/jpeg`, `image/svg+xml`
+uri = bounded_bytes
+
+; Custom user defined plutus data.
+; Setting data is optional, but the field is required
+; and needs to be at least Unit/Void: #6.121([])
+extra = plutus_data
+  
+datum = #6.121([metadata, 1, extra]) ; version 1
+```
+Example datum as JSON:
+```json
+{"constructor" : 0, "fields": [{"map": [{"k": {"bytes": "6E616D65"}, "v": {"bytes":"5370616365427564"}}, {"k": {"bytes": "6465736372697074696F6E"}, "v": {"bytes":"54686973206973206D79207465737420746F6B656E"}}, {"k": {"bytes": "696D616765"}, "v": {"bytes": "697066733A2F2F74657374"}}, {"k": {"bytes": "646563696D616C73"}, "v": {"int": 2}}]}, {"int": 1}]}
+```
+
+### Retrieve metadata as 3rd party
+
+A third party has the following SFT `d5e6bf0500378d4f0da4e8dde6becec7621cd8cbf5cbb9b87013d4cc.(444)TestToken` they want to lookup. The steps are
+
+1. Construct `reference NFT` from `user token`: `d5e6bf0500378d4f0da4e8dde6becec7621cd8cbf5cbb9b87013d4cc.(100)TestToken`
+2. Look up `reference NFT` and find the output it's locked in.
+3. Get the datum from the output and lookup metadata by going into the first field of constructor 0.
+4. Convert to JSON and encode all string entries to UTF-8 if possible, otherwise leave them in hex.
+
+### Retrieve metadata from a Plutus validator
+
+We want to bring the metadata of the SFT `d5e6bf0500378d4f0da4e8dde6becec7621cd8cbf5cbb9b87013d4cc.(444)TestToken` in the Plutus validator context. To do this we 
+
+1. Construct `reference NFT` from `user token`: `d5e6bf0500378d4f0da4e8dde6becec7621cd8cbf5cbb9b87013d4cc.(100)TestToken` (off-chain)
+2. Look up `reference NFT` and find the output it's locked in. (off-chain)
+3. Reference the output in the transaction. (off-chain)
+4. Verify validity of datum of the referenced output by checking if policy ID of `reference NFT` and `user token` and their asset names without the `asset_name_label` prefix match. (on-chain)
+
 ## Rationale
 
 Without seperation of `reference NFT` and `user token` you lose all flexibility and moving the `user token` would be quite cumbersome as you would need to add the metadata everytime to the new output where the `user token` is sent to. Hence you separate metadata and `user token` and lock the metadata inside another UTxO, so you can freely move the `user token` around.