document casa/viz boundary

docs/source/design/boundary.rst

@@ -0,0 +1,42 @@
+.. _design-system-design:
+
+CASA/Viz Boundary
+====================
+
+.. currentmodule:: design
+
+This document describes the boundary between CASA (including CASA7 and future versions of
+CASA). It is necessarily a high-level view of the principles of this boundary. However,
+it is important to layout the system level view of this boundary to prevent choices being
+made in the system design of other parts of the CASA and NRAO ecosystem.
+
+For this discussion, only two execution modes will considered. While the introduction describes
+the "Usage Settings" where we envison casagui being used. The "Usage Settings" describe
+the user context where CASA operates. The "Execution Modes" is the level below the "Usage Settings".
+This lower level is discussed here to motivate some constraints that are implied by the
+the implementaton which will support the "Usage Settings".
+
+In all of this current discussion, the assumption is that there is a GUI and that it is always
+running on the user's device. In practice, this means that the GUI will be presented in the
+user's browser. The execution that we are talking about is the execution process that creates
+images, provides storage for images, modifies images, or collates and organizes data. These
+processes could also be on the user's device, but they could also be running on remote systems.
+
+Local Execution
+-------------------
+
+With local execution, there is a local Python process which executes all of the image and data
+processing code. Communication between this Python process and the GUI code in the browser is
+accomplished with :xref:`websocket`. The user interacts with the elements of the GUI within
+the browser. These interactions result in :xref:`websocket` messages sent to the local Python
+environment. Within the Python environment, the interfaces provided by CASA and other packages
+is used to accomplish the desired processing, and the results are then returned to the GUI
+via websockets.
+
+
+Remote Execution
+-------------------
+
+Remote execution allows the user to start the GUI locally but perform the desired processing
+tasks on a remote system which the user can access with SSH.
+

docs/source/index.rst

@@ -21,6 +21,7 @@ primarily support Python users and developers using a terminal to interact with
    :caption: Contents:
 
    design/intro
+   design/boundary
    applications/intro
    python/casagui