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48 lines
2.0 KiB
ReStructuredText
48 lines
2.0 KiB
ReStructuredText
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Flows
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=====
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.. topic:: Summary
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* *Flows automate the process of agreeing ledger updates*
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* *Communication between nodes only occurs in the context of these flows, and is point-to-point*
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* *Built-in flows are provided to automate common tasks*
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Corda networks use point-to-point messaging instead of a global broadcast. This means that coordinating a ledger update
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requires network participants to specify exactly what information needs to be sent, to which counterparties, and in
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what order.
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Rather than having to specify these steps manually, Corda automates the process using *flows*. A flow is a sequence
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of actions that tells a node how to achieve a specific ledger update, such as issuing an asset or settling a trade.
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Once a given business process has been encapsulated in a flow and installed on the node as part of a CorDapp, the node's
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owner can instruct the node to kick off this business process at any time with a simple RPC call. All activity on the
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node, and all inter-node communication, occurs in the context of these flows.
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A flow's steps may include:
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* Identifying counterparties on the network
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* Extracting information from the vault or local storage
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* Building a transaction
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* Sending messages
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* Notarising and recording a transaction
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* Reporting progress to observers
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* Requesting human interaction...
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A node can have millions of flows active at once and they may last days, across node restarts and even upgrades.
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An example flow
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---------------
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Here is a visualisation of an example flow, showing Alice and Bob agreeing on a ledger update:
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.. image:: resources/flow.gif
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The flow library
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----------------
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Corda provides a library of flows to handle common tasks, meaning that developers do not have to redefine the
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logic behind common processes such as:
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* Notarising and recording a transaction
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* Gathering signatures from counterparty nodes
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* Verifying a chain of transactions
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Further information on the available built-in flows can be found in :doc:`flow-library`.
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