Open/Closed Layers in Layered Architecture
In a layered architecture, there are two kinds of layers: open and closed. In closed layers, the request comes from the above layers and has to go through all closed layers one by one to reach simple data in the bottom layer. For example, if the presentation layer only needs a simple string from a database, the request has to pass through all closed layers.
In open layers, the request can bypass layers (until it hits a closed layer) and get data from the bottom layer. If we think a presentation layer needs a string again, the presentation can directly request this string from the database without going through all layers (called the fast-lane reader pattern).
