First you will notice that the diagrams on this page are associated with only DC circuits and not AC, because of the reference to (+) and (-) polarities. Therefore, sinking and sourcing terminology applies only to DC input and output circuits. Input and output points that are sinking or sourcing can conduct current in one direction only. This means it is possible to connect the external supply and field device to the I/O point, with current trying to flow in the wrong direction, and the circuit will not operate. However, the supply and field device can be connected every time based on an understanding of sourcing and sinking.
The Kanban Board application is an example of a real-time, multi-user collaborative application. The Kanban Board application enables users to collaboratively create and edit Kanban boards and tasks. Changes made by one user to a board or a task are immediately visible to other users viewing the same board or task. It has a microservices architecture and is written using Java and Spring Boot and uses MongoDB for materialized views. The application uses STOMP-over-WebSockets to push events from the event store to an AngularJS front-end.
An example of this would be a system with lots of readers and a few writers. Using Event Sourcing this could be delivered as a cluster of systems with in-memory databases, kept up to date with each other through a stream of events. If updates are needed, they can be routed to a single master system (or a tighter cluster of servers around a single database or message queue) which applies the updates to the system of record and then broadcasts the resulting events to the wider cluster of readers. Even when the system of record is the application state in a database this could be a very appealing structure. If the system of record is the event log, there is are plenty of options for very high performance since the event log is a purely additive structure that requires minimal locking.