The Composer provides developers the capability to aggregate, manipulate, and mashup device data streams in a visual and intuitive way using a Web-based flow editor that makes it easy to wire together flows.
The Composer is a powerful composition tool build on Node-RED (http://nodered.org/) as shown in the following figure. Developers have a bunch of features for data manipulation: select data streams from a collection of devices and Web services; click and drop data streams on a canvas and connect them with flows for further modifications; combine many data streams into one, then sort, filter and manipulate it with basic operations. Finally, developers grab the composition and deploy it as mashup application on the glue.things runtime.
The Composer facilitates nodes for Web-enabled IoT devices and Web services. These mashups can be extended with condition statements, triggers and actions.
For example, developers can create a simple mashup for Beacons, Foursquare and Philips Hue. One option for a trigger can be: if someone enters a meeting room, then check-in this person on Foursquare and turn on the Philips Hue. Accordingly, this mashup can be deployed as Node.JS application with a RESTful API and input form for configuration and device settings. glue.things provides various trigger and actions nodes for devices and Web services.
Users are very fast in creating scenarios for the smart home application domain. Node-RED is extended from a developer tool
to an end-user application based on presets and guidelines.
You can find generic explanation about how composition works, here.