Transmissions Overview

Transmissions is a workflow compositor designed to carry out data processing operations as a series of relatively simple steps.

Terminology

Keywords :

• app
• mode
• transmission
• subtask
• processor
• dataset
• message
• module
• settings
• target

An app is a practical application of a collection of transmissions.

A transmission is a workflow description expressed in Turtle RDF. A collection of these appears in a transmissions.ttl file, which is a serialization of a dataset. This dataset is the primary definition of a Transmissions app. Within Transmissions a dataset is an RDF dataset (implemented using RDF-Ext and associated libraries). A transmission may be addressed individually as a subtask. At runtime a message, which is a JSON object is passed through the sequence of processors declared in the current transmission. Operation is event-driven. The runtime behaviours of the processors is determined by settings. A processor has a minimal interface as found in src/model/Processor.js. At runtime it receives a message, applies a process to the object, with parameters that may be provided via settings, and then passes on the result to the next processor in the transmission.

The mode refers to the manner in which an app is launched. This may be direct from the CLI, via the REPL or via a Web service. There is an auxiliary mode watch which relies on a long-running process. In this mode a change in a watched filesystem triggers an app run.

Settings are property values taken from the following sources, in descending order of priority :

1. current message - a JSON object
2. tt.ttl - target definition, a dataset
3. transmissions.ttl - transmissions definition, a dataset
4. config.ttl - default configuration, a dataset

In a full configuration, the app will comprise definitions from transmissions.ttl and config.ttl. Associated with these is an about.md which provides a human-readable description of the app. When run a target may be identified, which is a directory containing a tt.ttl files. Typically the directory will also contain data used by the app for that target. To enable creation of Transmissions apps which are loosely coupled to the

A lot of the codebase is work in progress.

Program Flow

Transmissions is typically launched using ./trans, which simply calls the entry point at src/api/cli/run.js. This parses the command-line args and passes them to src/api/common/CommandUtils.js which organises them into