Introduction

Those having experience in developing chaincode in Fabric know well how a chaincode looks like. In a nutshell, we define the data structure (state) for some assets, and functions which one can query the state, or invoke if change of state is needed. Since v2.1, Fabric team also introduces Contract API (link) which simplifies the way chaincode is written. This still follows the same pattern.

Recently I see another attempt to change the way we develop smart contracts with classes and objects, which is a favourite model for many developers. Prasaga introduces Extensible Blockchain Object Model, XBOM, in which assets are defined as objects and owned by accounts. XBOM provides a coding environment and methodology, which is currently implemented in Hyperledger Fabric for a permissioned chain offering and will be available on DataGrid Blockchain (DGB), an open permissionless chain in the future.

With XBOM, developers build applications with object oriented programming model, and XBOM provides an infrastructure serving them. The infrastructure (named Class Manager Infrastructure) then interacts with the underlying infrastructure, which is a fabric network in this case. Theoretically the developer does not care about the blockchain, as it is well handled by the infrastructure. That is the reason XBOM is positioned as “Decentralized GlobalOS”, like an operating system on top of the blockchain.

For those who are interested in this approach, the best way is to gain more information from their website. Here is the overview of XBOM.

The first available XBOM material is a set of chaincode in Golang. Since this summer they have published several videos. I have tried the code and here I document some of my experience and observation during my first attempt.

Some Concepts about XBOM

While you can always find good and official explanations on the material, here I try to provide some quick ideas about XBOM.

XBOM at a Glance

XBOM is a First-Class Object Model, meaning that everything is object in this environment. While the developers are dealing with the classes and objects in their code, these classes and objects are objects inside XBOM. XBOM provides a Class Manager Infrastructure such that developers can focus on their applications with their own classes and objects on a blockchain environment, without involving the chaincode and handling the ledger natively.

The Class Manager Infrastructure interacts with the underlying blockchain platforms. Taking Fabric as an example, each object is stored as a key-value pair in the ledger. The key is a unique identifier, called Ledger Object Identifier (LOID), and the value keeps all relevant information about this object. The Class Manager Infrastructure is responsible for interacting with the ledger storage, and is in fact a set of chaincode when it is implemented in Fabric.

We can see this approach in a layered representation, and compare this with traditional coding on Fabric environment (source: David’s slide shown in the video with some colour code).

Application developers are no longer coding at chaincode level. Instead they are working at object level. They will use the object transaction model provided by Class Manager Infrastructure. In general, each transaction is to specify which account context the transaction is working, the target object, method and input arguments for the method. The Class Manager Infrastructure processes the transaction and returns the output.

We will go in depth into how Class Manager Infrastructure works with the fabric network and ledger later in the demonstration.

Account, Ownership and Containment

Our demonstration is to create an account object. Here we introduce the concept of object containment in XBOM, and how account is associated with the containment. Each object has reference to a parent object or directly (and eventually) to an account object (Class Account). This forms a tree structure of objects. This model is good for providing ownership of assets (objects) to an account. (Source: David’s slide shown in the video.)

After bootstrap we have the first account: System Account. In the demonstration we are going to create a new account with the System Account. We will detail how this is done.

This is just a tip of an iceberg in XBOM, but should be good enough for the demonstration. You can always get the latest update on their site.

Demonstration and Illustration

The demonstration follows the material (videos) on XBOM website. You can find the video of how the demonstration works. Meanwhile I make some illustrations and observations about the demonstration.

Video sources

• Quick Start https://www.youtube.com/watch?v=dNAkDeLpG2Y
• Overview #1 https://www.youtube.com/watch?v=2P37UmQpI3g
• Overview #3 https://www.youtube.com/watch?v=x_FnXb6u3b8

A Ubuntu 18.04 LTS server on AWS EC2 is instantiated for demonstration. The code and installation instruction is available here through registration.

We broadly divide the demonstration into two steps.

Step 1 is mainly on Fabric operation. The fabric network follows the Test-Network in fabric-samples with modification. In particular, a script classmanager.sh is created to perform all the tasks. This classmanager.sh largely follows network.sh in Test-Network. During the whole demonstration we use classmanager.sh to perform all the tasks, including bringing up the network, deploying the Class Manager Infrastructure and bootstrapping all components. After Step 1 we have a Class Manager Infrastructure ready for our next step.

Step 2 focuses on Class Manager Infrastructure. We will interact with objects provided in the Class Manager Infrastructure. All commands are working in this layer, and Class Manager Infrastructure is handling the relevant activities in chaincode invocation. During the demonstration we will take a look at what happens in the ledger. This gives us a better understanding about how Class Manager Infrastructure is interacting with the Fabric. Our task is to create a new Account object, and after that we will use “inspect” method from the Class Object to take a look at the new Account object.

Step 1: Bring Up Class Manager Infrastructure

Step 1.1: Bring up modified Test Network and Create Channel

This brings up a sample network, following the Test Network in Hyperledger Fabric 2.0+. It contains three organizations. One orderer organization and two peer organizations. A channel mychannel is created and the two peer organizations join this channel.

./classmanager.sh up createChannelor./classmanager.sh up createChannel -s couchdb

Note: couchdb can be used as the world state database for each peer with -s couchdb.

Step 1.2: Deploy Class Manager Infrastructure

Class Manager Infrastructure is a set of chaincode designed with the purpose of building the Class Manager Infrastructure. It uses the standard lifecycle chaincode to deploy this set of chaincode to the Fabric network.

./classmanager.sh deployCC

After deployment, it is what we observe in the ledger. We see a database is created on the channel (mychannel) and chaincode (classmanager).

./classmanager.sh InitBootstrap -loid default

./classmanager.sh Invoke -ic '{"Args":["GetSystemAccountObject"]}'

Step 2.2: Get Root Dictionary Object

./classmanager.sh Invoke -ic '{"Args":["GetRootDictionary"]}'

We now have the Root Dictionary object: [82, 111, 111, 116, …]

./classmanager.sh Invoke -ic '{"Args":["ObjectSend","[83,121,115,116,101,109,65,99,99,111,117,110,116,79,98,106,101,99,116,0,0,0,0,0,0,0,0,0,0,0,0,0]","[82,111,111,116,68,105,99,116,105,111,110,97,114,121,76,79,73,68,0,0,0,0,0,0,0,0,0,0,0,0,0,0]","{\"Mtdstring\":\"ClassDictionary_GetObjectByName\"}","{\"ObjectPathName\":\"RootAccountManager\"}"]}'

./classmanager.sh Invoke -ic '{"Args":["ObjectSend","[83,121,115,116,101,109,65,99,99,111,117,110,116,79,98,106,101,99,116,0,0,0,0,0,0,0,0,0,0,0,0,0]","[44,32,80,101,53,74,36,52,35,113,59,53,46,50,89,84,97,56,35,92,98,95,35,66,96,32,90,118,81,80,89,68]","{\"Mtdstring\":\"ClassFactory_NewObject\"}","{\"NewCount\":1}"]}'

./classmanager.sh Invoke -ic '{"Args":["ObjectSend","[83,121,115,116,101,109,65,99,99,111,117,110,116,79,98,106,101,99,116,0,0,0,0,0,0,0,0,0,0,0,0,0]","[45,38,60,97,79,122,35,32,42,105,59,110,88,54,43,43,80,80,49,116,38,43,55,123,58,33,102,79,50,44,95,43]","{\"Mtdstring\":\"ClassObject_Inspect\"}","{\"Unused\":0}"]}'

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