Subscribing Basics

What is subscribing?

Subscribing in OpenDataDSL refers to one of the following:

• Event-driven data flows

  Take an automatic action based on information changes

• Real-time data changes

  React to data changes in real-time

What can you subscribe to?

There are minor differences between the 2 different method of subscription which are explained here:

Event-driven subscriptions

With event-driven subscriptions, as well as the entity type and id, you can specify the action taken from the following:

• Create
• Update
• Delete
• Tag
• All

Real-time subscriptions

For real-time subscriptions, you subscribe to the id of the entities you want to listen for, and the action that is taken using a method in the format:

• On{entity}Create - e.g. OnObjectCreate
• On{entity}Update - e.g. OnObjectUpdate
• On{entity}Delete - e.g. OnObjectDelete

With real-time subscriptions, you can also listen for process and process execution messages using:

• OnExecutionMessage
• OnProcessMessage

Entities

The following table shows the entities that can be subscribed to by each method:

Entity	Event-Driven	Real-Time
Data Updates
Object (Master Data)	yes	yes
Data - timeseries	yes	yes
Data - curve	yes	yes
Data - matrix	yes	yes
Event	yes	yes
Report	yes	-
Calendar	yes	yes
Expiry Calendar	yes	yes
Action	-	yes
Workflow	-	yes
Server Events
Process Execution Message	-	yes
Process Run	-	yes

Event-driven data flows

Event-driven data flows refer to a design pattern or architecture where data processing and communication happen in response to events or changes in the system. In this pattern, events trigger the flow of data through a system, where each event is processed independently, and a corresponding action is taken based on the event.

What does a subscription look like?

A subscription has the following properties:

Name	Description	Type
_id	Unique Id	ObjectId
name	Name of the subscription	String
description	Description of the subscription	String
enabled	Flag to enable/disable this subscription	Boolean
system	Flag to say whether this subscription is system managed and cannot be changed	Boolean
environment	The name of the environment to run in (default production)	String
objects	An array of items to subscribe to	Array of subscription items
targets	An array of target actions to call	Array of subscription targets

Subscription Item details

Name	Description	Type
_id	Unique Id	ObjectId or String
key	A name that this item is referred to as	String
service	The name of the service this item belongs to	String
id	The id of the item to subscribe to	String
action	The action to subscribe to (create/update/delete/tag/all)	String

Subscription Target details

Name	Description	Type
name	The target name, e.g. EmailTarget	String

The rest of the properties for the subscription target are specific to the type of target

What actions can be taken?

In OpenDataDSL, as of today, you can perform one of the following event-driven actions (known as targets):

• Build a forward curve

  Usually when the input data for a curve is updated you would want to build a smart curve

• Send an email

  Use the updated data and a template to send a HTML email to a user or users

• Run a process/workflow

  Trigger a process to run possibly to load some other data

• Publish the data to another tenant

  Another independent tenant can be updated with this data

• Send the data to a message queue

  Send the updated data as a message to be consumed by a downstream system

• Run a report

  Run a report, maybe aggregating data from other sources

• Run an ODSL script

  The possibilities are endless, maybe you want to perform some derivations based on the updated data

• Write a blob to an Azure Storage Container

  Writes the data to a blob in a container, this can be used to trigger other Azure Middleware Services

Real-time data changes

The underlying infrastructure for OpenDataDSL real-time is SignalR.

SignalR is an open-source real-time communication framework developed by Microsoft. It simplifies the process of adding real-time web functionality to applications by enabling bi-directional communication between the server and client.

SignalR supports multiple client platforms, including web browsers (JavaScript), .NET, Xamarin, and other platforms through the use of client libraries. It provides a unified API for working with these different client platforms.

Key features of SignalR include:

• Real-time updates

  SignalR enables real-time communication, allowing the server to push updates to connected clients instantly.

• Scalability

  SignalR can scale to handle a large number of concurrent connections by using techniques like message queuing and distributed caching.

• Cross-platform support

  SignalR provides client libraries for various platforms, allowing developers to build real-time applications across different devices and technologies.

• Automatic reconnection

  SignalR handles automatic reconnection for clients in case of network interruptions or server restarts, ensuring a seamless user experience.

• Security

  SignalR includes features for authentication and authorization, allowing developers to secure their real-time applications.