First a rough description.

At the bottom of the picture is a bus "at-spi dbus" that has connections up to 7 applications.
At the bottom, the  bus has connections to two boxes: "at-spi-registryd" and "Orca".
The box Orca has a component "py at spi".

Now a detailed description.

Applications are listed from left to right, all have a name and contain more or less "boxes"
connected to each other by arrows.
The last component is always connected to the bus.

*   GTK 2/3 app: GTK <-> gail <-> ATK <-> atk-bridge
*   Java app: Swing <-> Java-atk-wrapper <-> ATK <-> atk-bridge
*   Mozilla: XUL <-> NSI Access  <-> ATK  <-> atk-bridge
*   QT4 app: Qt4  <-> qt-at-spi

the last three applications contain only one box.

*   Qt5 app: Qt5 gui,
*   GTK4 app: gtk4
*   Egui Unity: AccessKit

The bus has two arrow paths:

1.  This one connects the last components of all applications and the component "py at spi" within
2.  The other arrow route has an arrow pointing to “at-spi-registryd” in addition to all the
    connections of the first arrow route

Finally, there is a double arrow connection between "at-spi-registryd" and "py-at-spi".