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In Flowgear, Integrations are created visually as Workflows. Workflows contain elements called Nodes that represent specific tasks and are linked together using Flow Connectors. Flow Connectors allow you to sequence order of execution of Nodes as well as map flow of data between Nodes.
Workflows execute in pulses from left to right, rather than cyclically. Control passes from the currently executing Node to all Nodes connected to the right of it, until there are no more connected Nodes.
Workflows can run on-demand or continuously (called AutoStart). When a Workflow is designed for AutoStart, it usually contains a Trigger Node which is one of the first Nodes to execute. Triggers block until a condition is met and when present in a Workflow, control returns to the earliest Trigger again once all downstream Nodes have finished executing.
In on-demand mode, Workflows can be run by an end-user from within the Flowgear Console or called via the Flowgear API. Workflows often have input and output properties (ie. a data contract) that enable a user or a consumer to specify parameters and receive results. These properties are defined using a special Node called a Variable Bar.
Nodes are categorised by their function:
Developers can create their own Nodes for private use or share them with the Flowgear community.
Currently, all Node submissions are reviewed by Flowgear prior to publishing. Refer to Building Nodes for information on creating your own Nodes.
It is frequently necessary to connect to data sources that are either not exposed to the Internet (for example, a web service behind a firewall) or have stateful API's that are not web-transportable (for example, COM API's).
In these scenarios, a software agent called a DropPoint can be installed on an application or database server in order to gain access to the data source. A Connection specifies the endpoint and credentials for a data source and optionally allows users to select a DropPoint on which the Node should execute.
DropPoints are not simply proxies, they dynamically acquire and execute Node assemblies/binaries and can therefore be used to connect to endpoints other than web services. DropPoints also recover from disruption to Internet connectivity and tasks may appear to take longer to execute than usual if a disruption occurs while a Node is executing.