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BPMN execution engine on Ethereum

Caterpillar is a Business Process Management System (BPMS) prototype that runs on top of Ethereum and that relies on the translation of process models into smart contracts. More specifically, Caterpillar accepts as input a process model specified in BPMN and generates a set of smart contracts that captures the underlying behavior. The smart contracts, written in Ethereum's Solidity language, can then be compiled and deployed to the public or any other private Ethereum network using standard tools. Moreover, Caterpillar exhibits a REST API that can be used to interact with running instances of the deployed process models.

Caterpillar also provides a set of modelling tools and an execution panel (in releases v1.0, 2.0 and 2.1) which interact with the underlying execution engine via the aforementioned REST API. The latter can also be used by third party software to interact in a programmatic way via Caterpillar with the instances of business process running on the blockchain.

Caterpillar’s code distribution in this repository contains three different folders in v1.0 and two in v2.0, v2.1 and v3.0. The folder caterpillar_core includes the implementation of the core components, execution_panel consists of the code of a BPMN visualizer that serves to keep track of the execution state of process instances and to lets users check in process data. The services_manager folder contains the implementation for an external service which is used only in v1.0 for demonstration purposes. In v2.1, the source code is in the folder labelled as "prototype". Besides, the folder "Dynamic Binding Example" contains the binding policy and BPMN model used as running example in

The approach implemented by the v2.0 corresponding to the compilation-based engine can be accessed from: (paper at journal Sowtware: Practice and Experience) or (preprint).

The paper describing the Role Dynamic Binding and Access Control implemented by v2.1 can be accessed from: (conference paper presented at CAISE'19) or (preprint). More detailed documentation on how to use Caterpillar (v2.0 and v2.1) can be found at:

The paper describing the interpretation-based engine implemented by v3.0 can be accessed from: (conference paper presented at EDOC'19) or (preprint)

Additionally, a demo paper about v1.0: can be accessed from: We are keping the source code of v1.0 as a reference, although we are not currently working on such an implementation.

We are currently developing the release labeled caterpillar-full (REST API - backend), which puts together the code of the releases v2.0, v2.1 and v3.0 into a single system instead of handling them as separated versions. The most recent release also migrates the system to the latest versions of the libraries (see package.json file), removing compatibility issues in v2.0, v2.1 and v3.0 (e.g., with web3, solc, node.js, etc.), which use older versions. Besides, we also refactored the code to increase readability, modularity, and reusability of the system. IMPORTANT: The release caterpillar-full (REST API - backend) exposes the functionalities of Caterpillar through a REST API, i.e., there is no visual interface like the frontend application implemented by the execution-panel in the releases v2.0 and v2.1. We are currently designing a developing a new execution-panel (frontend application) whose release is expected by the beginning of 2021.

For running Caterpillar locally, download the source code from the repository and follow the next steps to set up the applications and install the required dependencies. For running caterpillar from a Docker image go directly to the last section of this document. Be aware that the Docker image works only on the version v1.0.

Installing Ganache CLI

By default, the core of Caterpillar was configured to run on top of Ganache CLI which is a Node.js based Ethereum client for testing and development. It uses ethereumjs to simulate full client behavior and make developing Ethereum applications. All the instructions about the installation can be found here: However, the Ethereum Provider can be updated at the beginning of the source code in the controller "caterpillar-core/src/models/models.controller.ts" (check the comments).

Note that Ganache CLI is written in Javascript and distributed as a Node package via npm. Make sure you have Node.js (>= v6.11.5) installed. Besides, be aware to start the Ganache CLI server before running the applications Caterpillar Core and Services Manager. In that respect, you only need to open a terminal on your computer and run the command:


How to use Caterpillar Core

Before running Caterpillar Core, make sure you installed gulp-cli running the command: npm install gulp-cli -g. All the instructions about the glup-cli installation can be found here:

Additionally, the version v2.0 uses a process repository to store and access metadata produced by Caterpillar when compiling the BPMN model into Solidity smart contracts. Currently, this repository was implemented on top of MongoDB which is a database that stores data as JSON-like documents. The instructions to install MongoDB Community Edition can be accessed from here:

To set up and run the core, open a terminal in your computer and move into the folder caterpillar_core.

For installing the dependencies, run the commands

 npm install
 gulp build

For running the application you may use one of the following commands

 node ./out/www.js

By default the application runs on http://localhost:3000.

Make sure you have Ganache Cli running in your computer before starting the core. Besides, if you are using the version v2.0 a MongoDB client must be also running.

The application provides a REST API to interact with the core of Caterpillar. The following table summarizes the mapping of resource-related actions:

Verb URI Description
POST /models Registers a BPMN model (Triggers also code generation and compilation)
GET /models Retrieves the list of registered BPMN models
GET /models/:mid Retrieves a BPMN model and its compilation artifacts
POST /models/:mid Creates a new process instance from a given model
GET /processes/ Retrieves the list of active process instances
GET /processes/:pid Retrieves the current state of a process instance
POST /workitems/:wimid/:wiid Checks-in a work item (i.e. user task)
POST /workitems/:wimid/:evname Forwards message event, delivered only if the event is enabled

(ONLY FOR v1.0) If the process model has service tasks and consequently needs to interact with the services manager application, then you must run the services manager application and create the corresponding services before running Caterpillar core.

From the caterpillar_core folder, it is possible to run the script:

 node demo_running_example_test.js

Which is provided only for the version v1.0, to register, create an instance and get the address of a sample process provided in the file demo_running_example.bpmn. For running the sample process, it is also required to run first the application services_manager and to register the external services.

Updates in v2.1

The version v2.1 extends v2.0 with an Access Control mechanism, based on a role dynamic binding policy. Accordingly, the REST API to interact with the core of Caterpillar was extended with the following resource-related actions.

Verb URI Description
POST /registry Deploys a new instance of the Runtime Registry
POST /resources/policy Generates/Deploys the contracts from a given binding policy specification (BPF)
POST /resources/task-role Generates/Deploys the contract mapping the roles to the tasks in a given BPMN model
POST /resources/nominate Nominates an actor into a role as defined in the BPF
POST /resources/release Releases an actor from a role as defined in the BPF
POST /resources/vote Accepts/Rejects the nomination/release of an actor as defined in the BPF
GET /resources/:role/:pAddr Retrieves the current state of an actor into a role in a process instance

The grammar describing the Binding Policy Specification can be found at:

The full description of the language and Dynamic Role Binding can be found at:

How to use Services Manager (ONLY FOR v1.0)

Open a terminal in your computer and move into the folder services_manager.

For installing the dependencies, run the comand

 npm install
 gulp build

For running the application use the comand

 node ./out/www.js

By default the application will runs on http://localhost:3010.

The application provides a REST API to interact with services manager. The following table summarizes the mapping of resource-related actions:

Verb URI Description
POST /services Registers an external service
GET /services Retrieves the list of registered external services
GET /services/:sid Retrieves smart contract/address of an external service

From the services_manager folder is possible to run the script

 node oracle_creation.js

to register the services required by the running example provided in the core.

How to use Execution Panel (ONLY FOR V2.0 and V2.1)

Before running the Execution Panel, make sure you installed angular-cli:

To set up and run the execution panel, open a terminal in your computer and move into the folder execution-panel.

For installing the dependencies, run the comand

 npm install

For running the application use the comand

 ng serve

Open a web browser and put the URL http://localhost:4200/.

You must use the button refresh to update the instances running, and then select one of the URLs obtained that will contain the address when it is running the smart contract. Then press the button Open. Here, you can see the enabled activities visualized in dark green. For executing any enabled activity, just click on it and fill the parameter info if required. All the execution of the process (including internal operations) can be traced from the terminal of caterpillar_core.

Running Caterpillar from a Docker Image (ONLY FOR v1.0)

It is also possible to execute Caterpillar from a Docked Image without needing to install all the dependencies required to run the applications locally. For that, it is necessary only to install Docker ( on your computer, then open a terminal and run the comand:

 docker run --rm -it -p 3200:3200 -p 3000:3000 -p 8090:8090 orlenyslp/caterpillar-demo:v1

Initially, you will see in the terminal, the creation of two services that are necesary for running the running example provided in When the terminal displays the message "Listening on port 3000", it means that the core is running and then open a web browser to interact with execution panel that will be running in the URL http://localhost:3200/.

The execution panel provides a simple interface to interact with the core. The following options are available:

  • Creating and uploading bpmn models by clicking the button with the corresponding name. From the modeler, when you press save, the request is sent to the core. The information about the creation, compilation, and deploy of the smart contracts will be displayed in the terminal where the Docker container is running. If the model was successfully compiled, then a link to display its information will appear on the dashboard with the format <model_identifier>:<model_name>.

After upload the running example, it is necessary to go to the documentation section for both service tasks and to replace the strings labeled as $Assess_Loan_Risk_Address and $Appraise Property_Address with the corresponding addresses where the services are running. These addresses were displayed in the terminal when the Docker container starts running.

  • Searching and displaying all the process model created in the current running of the container. The search will retrieve every model whose name or identifier contains the input as a substring. Empty searches will generate all the models created until now.

  • Displaying the solidity code generated from the process model and create new instances. From the dashboard, click the link to display the information of the desired process model. Here, there are accessible the solidity code and the active instances. There are also provided two buttons that allow the creation and updating of running instances. The button labeled with "Refresh instances" will remove from the list all the addresses to processes instances whose execution was concluded.

  • Executing process instances. By clicking on the address of the desired instance, it will be displayed a viewer that allows the visualization of the active tasks (in dark green) that can be executed by clicking on them. The viewer also allows switching to each active instance of the process. Every time a new instance is selected, the button labeled with "Go" must be pressed to display the current status of the instance.

All the results of the queries performed by the execution panel to the caterpillar core through the REST API will appear also in the terminal where the docker container is running.


Caterpillar: A BPMN-based BPMS for Ethereum







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