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69 lines
3.9 KiB
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69 lines
3.9 KiB
ReStructuredText
.. highlight:: kotlin
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.. raw:: html
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<script type="text/javascript" src="_static/jquery.js"></script>
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<script type="text/javascript" src="_static/codesets.js"></script>
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Where to start
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==============
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So you want to start experimenting with Corda. Where do you begin? Although Corda is still very early and missing
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large chunks of important functionality, this article will hopefully put you on the right place.
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An experiment with Corda is started by picking a *scenario* and then turning it into a *demo*. It is important to
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understand that at this stage in its life, Corda does not have a single unified server that loads everything
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dynamically. Instead, Corda provides an object oriented API which is then used by a *driver* program, with one driver
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per scenario. You can see the existing demo apps in action by :doc:`running-the-demos`.
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In future this design will change and there will be a single server that does everything. But for now, there isn't.
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A scenario contains:
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* A set of participating nodes and their roles.
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* Some business process you wish to automate (typically simplified from the real thing).
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* The smart contracts and protocols that will automate that process.
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It may also specify a REST/JSON API, but this is optional.
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Here's are two example scenarios included in the box:
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1. Bank A wishes to buy some commercial paper in return for cash. Bank B wants to issue and sell some CP to Bank A.
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This is probably the simplest scenario in Corda that still does something interesting. It's like the buttered
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bread of finance.
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2. Bank A and Bank B want to enter into an interest rate swap and evolve it through its lifecycle.
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The process of implementing a scenario looks like this:
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1. First of all, design your states and transaction types. Read about the :doc:`data-model` if you aren't sure what that
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involves.
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2. Now, create a new file in the contracts/src/main directory. You can either any JVM language but we only provide examples
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in Java and Kotlin. The file should define your state classes and your contract class, which will define the
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allowable state transitions. You can learn how these are constructed by reading the ":doc:`tutorial-contract`" tutorial.
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3. It isn't enough to just define static data and logic that controls what's allowed. You must also orchestrate the
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business process. This is the job of the protocol framework. You can learn how to author these by reading
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":doc:`protocol-state-machines`".
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4. Once you have created your states, transactions and protocols, you need a way to demonstrate them (outside of the
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unit tests, of course). This topic is covered below.
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The trader demo
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---------------
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Until Corda has a unified server that can dynamically load every aspect of an application (i.e. software implementing a scenario),
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we have to do a bit of copy/paste wiring ourselves.
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The trader demo is a good place to start understanding this, which can be found in src/main/kotlin/demos/TraderDemo.kt
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The idea of a driver program is that it starts a node in one of several roles, according to a command line flag. The
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driver may step through some pre-programmed scenario automatically or it may register an API to be exported via HTTP.
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You would then have to drive the node externally for your demo.
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The best way to create your own scenario is not to write a driver from scratch but to copy the existing trader or IRS
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demo drivers and then customise them, as much of the code would end up being shared (like for command line parsing).
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Things you will want to adjust:
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1. The name of the grouping directory each node role will create its private directory under.
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2. The demo protocols that just wrap the real business process in some kind of fake trading logic.
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The IRS driver program registers REST APIs, but as this is seriously in flux right now and the APIs will change a lot,
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we do not recommend you try this as part of your initial explorations unless you are feeling adventurous. |