Sitefinity Publishing System: A Brief Walkthrough

In the publishing system you have Inbound Pipes, Publishing Point and Outbound Pipes. What are their purposes? First we have a publishing point - this is the place where we accumulate the data from different sources. We have 2 types of publishing points out of the box - persistent and pass through. Persistent pipes store the data into the database and the pass through immediately push the data that is received. The data is coming from the inbound pipes into the publishing point and after that is processed by the outbound pipes. On the other hand, we have Push and Pull pipes. Push pipes pass the data to the publishing point when they receive it. Pull pipes expect someone to request to get the data from them. With this you can have various scenarios like:

1. 1.    Push Pipes, Persistent Point and Pull Pipes.
2. 2.    Push Pipes, Pass through Point and Push Pipes
3. 3.    Pull Pipes, Pass through Point and Pull Pipes.

The first scenario is very useful when you import data from somewhere and you want to store it. With this approach, you collect data which you cannot guarantee that will exist upon the request from the external source  (for example importing an RSS feed).
The second scenario is useful in cases when you want to flush some data from the Sitefinity CMS into some external source like Twitter, but you don’t want to persist this data.

The third option is good for scenarios like RSS in Sitefinity – you have the data and there is no need to duplicate it in the publishing point.

You can also have a combination between Pull and Push pipes on both sides of the publishing point.

The publishing system is invoked every time when you save item with the Fluent API. This creates a Schedule Task that will invoke the publishing system in a background thread.  

Basically this is the brief explanation of the Publishing System concept.
 
I have attached a sample of how can you create custom pipes.