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In this section, we will explore the different kinds of transactions available on Planetmint, as well as the role of cryptoconditions and contracts and its integration into Planetmint.
In Planetmint, transactions are used to register, issue, create or transfer things (e.g. assets). Transactions are the most basic kind of record stored by Planetmint.
There are two kinds:
- CREATE transactions, and
- TRANSFER transactions.
Below is an tabular overview about the changes.
A CREATE transaction can be used to register, issue, create or otherwise initiate the history of a single thing (or asset) in Planetmint. For example, one might register an identity or a creative work. The items are often called “assets”, but they might not be literal assets.
Planetmint supports divisible assets as of Planetmint Server v0.8.0. That means you can create/register an asset with an initial number of “shares.” For example, A CREATE transaction could register a truckload of 50 oak trees. Each share of a divisible asset must be interchangeable with each other share; the shares must be fungible.
A CREATE transaction can have one or more outputs. Each output has an associated amount: the number of shares tied to that output. For example, if the asset consists of 50 oak trees, one output might have 35 oak trees for one set of owners, and the other output might have 15 oak trees for another set of owners.
Each output also has an associated condition: the condition that must be met (by a TRANSFER transaction) to transfer/spend the output. Planetmint supports a variety of conditions. For details, see Transaction Components: Conditions in the relevant Planetmint Transactions Spec.
Example Planetmint CREATE transaction
Above we see a diagram of an example Planetmint CREATE transaction. It has one output: Pam owns/controls three shares of the asset, and there are no other shares (because there are no other outputs).
Each output also has a list of all the public keys associated with the conditions on that output. That list might be interpreted as the list of “owners.” A more accurate word might be fulfillers, signers, controllers, or transfer enablers. See the section titled A Note about Owners in the relevant Planetmint Transactions Spec.
A CREATE transaction must be signed by all the owners. (If you’re looking for that signature, it’s in the one “fulfilment” of the one input, albeit encoded.)
A TRANSFER transaction can transfer/spend one or more outputs on other transactions (CREATE transactions or other TRANSFER transactions). Those outputs must all be associated with the same asset; a TRANSFER transaction can only transfer shares of one asset at a time.
Each input on a TRANSFER transaction connects to one output on another transaction. Each input must satisfy the condition on the output it’s trying to transfer/spend.
A TRANSFER transaction can have one or more outputs, just like a CREATE transaction (described above). The total number of shares coming in on the inputs must equal the total number of shares going out on the outputs.
Above, we see a diagram of two example Planetmint transactions, a CREATE transaction and a TRANSFER transaction. The CREATE transaction is the same as in the earlier diagram. The TRANSFER transaction spends Pam’s output, so the input on that TRANSFER transaction must contain a valid signature from Pam (i.e. a valid fulfilment). The TRANSFER transaction has two outputs: Jim gets one share, and Pam gets the remaining two shares.
Terminology: The “Pam, 3” output is called a “spent transaction output”, and the “Jim, 1” and “Pam, 2” outputs are called “unspent transaction outputs” (UTXOs).
Example 1: Suppose a red car is owned and controlled by Joe. Suppose the current transfer condition on the vehicle says that any valid transfer must be signed by Joe. Joe could build a TRANSFER transaction containing an input with Joe’s signature (to fulfil the current output condition) plus a new output condition saying that any valid transfer must be signed by Rae.
Example 2: Someone might construct a TRANSFER transaction that fulfils the output conditions on four previously-untransferred assets of the same asset type, e.g. paperclips. The amounts might be 20, 10, 45 and 25, say, for a total of 100 paper clips. The TRANSFER transaction would also set up new transfer conditions. For example, maybe a set of 60 paperclips can only be transferred if Gertrude signs, and a separate set of 40 paperclips can only be transferred if both Jack and Kelly sign. Note how the sum of the incoming paper clips must equal the sum of the outgoing paperclips (100).
When a node is asked to check if a transaction is valid, it checks several things. This got documented by a BigchainDB post (previous version of Planetmint) atThe BigchainDB Blog: "What is a Valid Transaction in BigchainDB?" (Note: That post was about Planetmint Server v1.0.0.)
Planetmint utilizes IPLD (interplanetary linked data) marshalling and CIDs (content identifiers) to store and verify data. Before submitting a transaction to the network the data is marshalled using py-ipld and instead of the raw data a CID is stored on chain.
The CID is a self describing data structure. It contains information about the encoding, cryptographic algorithm, length and the actual hashvalue. For example the CID
bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzditells us the following:
Codec: dag-pb (MerkleDAG protobuf)
Digest (Hex): C3C4733EC8AFFD06CF9E9FF50FFC6BCD2EC85A6170004BB709669C31DE94391A
With this information we can validate that information about an asset we've received is actually valid.
The changes from version v2.0 on are as follows:
Planetmint has been developed with simple logical gateways in mind. The logic got introduced by cryptoconditions. The cryptocondition documentation contains all details about how conditoins are defined and how they can be verified and fulfilled.
The integration of such into the transaction schema of Planetmint is shown below.