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Functions Definition Language Composer

Writing an entire workflow in plain text could be a difficult task for many users. To simplify the process you can use FDL Composer, a web-based user interface to facilitate the definition of FDL YAML files for OSCAR and SCAR.


How to access FDl Composer

It does not require to be installed. Just access FDL Composer web. If you prefer to execute it on your computer instead of using the web, clone the git repository by using the following command:

git clone

And the run the app with npm:

npm start

Basic elements

Workflows are composed of OSCAR services and Storage providers:

OSCAR services

OSCAR services are responsible for processing the data uploaded to Storage providers.

Defining a new OSCAR service requires filling at least the name, image, and script fields.

To define environment variables you must add them as a comma separated string of key=value entries. For example, to create a variable with the name firstName and the value John, the "Environment variables" field should look like firstName=John. If you want to assign more than one variable, for example, firstName and lastName with the values John and Keats, the input field should include them all separated by commas (e.g., firstName=John,lastName=Keats).

Storage providers and buckets/folders

Storage providers are object storage systems responsible for storing both the input files to be processed by OSCAR services and the output files generated as a result of the processing.

Three types of storage providers can be used in OSCAR FDLs: MinIO, Amazon S3, and OneData.

To configure them, drag the storage provider from the menu to the canvas and double click on the item created. A window with a single input will appear. Then, insert the path of the folder name. To edit one of the storage providers, move the mouse over the item and select the edit option.

Remember that only MinIO can be used as input storage provider for OSCAR services.

Download and load state

The graphic workflow can be saved in a file using the "Download state" button. OSCAR services, Storage Providers, and Buckets are kept in the file. The graphic workflow can be edited later by loading it with the "Load state" button.

Create a YAML file

You can easily download the workflow's FDL file (in YAML) through the "Export YAML" button.

Connecting components

All components have four ports: The up and left ones are input ports while the right and down ports are used as output. OSCAR Services can only be connected with Storage providers, always linked in the same direction (the output of one element with the input of the other).

When two services are connected, both will be declared in the FDL file, but they will work separately, and there will be no workflow between them. If two storage providers are connected between them, it will have no effect, but both storages will be declared.

SCAR options

FDL Composer can also create FDL files for SCAR. This allows to define workflows that can be executed on the Edge or in on-premises Clouds through OSCAR, and on the public Cloud (AWS Lambda and/or AWS Batch) through SCAR.


There is an example of fdl-composer implementing the video-process use case in our blog.