2017-11-01 11:34:59 +00:00
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Hello, World!
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=============
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.. toctree::
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:maxdepth: 1
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hello-world-template
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hello-world-state
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hello-world-flow
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hello-world-running
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2017-06-16 13:05:52 +00:00
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By this point, :doc:`your dev environment should be set up <getting-set-up>`, you've run
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:doc:`your first CorDapp <tutorial-cordapp>`, and you're familiar with Corda's :doc:`key concepts <key-concepts>`. What
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comes next?
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2017-11-01 11:34:59 +00:00
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If you're a developer, the next step is to write your own CorDapp. CorDapps are plugins that are installed on one or
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more Corda nodes, and give the nodes' owners the ability to make their node conduct some new process - anything from
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2017-06-16 13:05:52 +00:00
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issuing a debt instrument to making a restaurant booking.
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Our use-case
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------------
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2017-11-01 11:34:59 +00:00
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Our CorDapp will model IOUs on-ledger. An IOU – short for “I O(we) (yo)U” – records the fact that one person owes
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another person a given amount of money. Clearly this is sensitive information that we'd only want to communicate on
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a need-to-know basis between the lender and the borrower. Fortunately, this is one of the areas where Corda excels.
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Corda makes it easy to allow a small set of parties to agree on a shared fact without needing to share this fact with
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everyone else on the network, as is the norm in blockchain platforms.
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2017-06-16 13:05:52 +00:00
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2017-11-01 11:34:59 +00:00
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To serve any useful function, our CorDapp will need at least two things:
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2017-06-16 13:05:52 +00:00
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2017-11-01 11:34:59 +00:00
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* **States**, the shared facts that Corda nodes reach consensus over and are then stored on the ledger
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* **Flows**, which encapsulate the procedure for carrying out a specific ledger update
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2017-06-16 13:05:52 +00:00
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2017-11-01 11:34:59 +00:00
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Our IOU CorDapp is no exception. It will define both a state and a flow:
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2017-06-16 13:05:52 +00:00
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2017-11-01 11:34:59 +00:00
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The IOUState
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^^^^^^^^^^^^
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Our state will be the ``IOUState``. It will store the value of the IOU, as well as the identities of the lender and the
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borrower. We can visualize ``IOUState`` as follows:
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2017-06-16 13:05:52 +00:00
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.. image:: resources/tutorial-state.png
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:scale: 25%
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:align: center
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2017-11-01 11:34:59 +00:00
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The IOUFlow
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^^^^^^^^^^^
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Our flow will be the ``IOUFlow``. This flow will completely automate the process of issuing a new IOU onto a ledger. It
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is composed of the following steps:
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2017-06-16 13:05:52 +00:00
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2017-07-07 11:06:28 +00:00
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.. image:: resources/simple-tutorial-flow.png
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2017-06-16 13:05:52 +00:00
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:scale: 25%
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:align: center
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2017-11-01 11:34:59 +00:00
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In traditional distributed ledger systems, where all data is broadcast to every network participant, you don’t need to
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think about data flows – you simply package up your ledger update and send it to everyone else on the network. But in
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Corda, where privacy is a core focus, flows allow us to carefully control who sees what during the process of
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agreeing a ledger update.
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2017-06-16 13:05:52 +00:00
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Progress so far
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---------------
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2017-11-01 11:34:59 +00:00
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We've sketched out a simple CorDapp that will allow nodes to confidentially issue new IOUs onto a ledger.
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2017-06-16 13:05:52 +00:00
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2017-11-01 11:34:59 +00:00
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Next, we'll be taking a look at the template project we'll be using as the basis for our CorDapp.
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