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10.3.1 How Connections Work


The NExS connection mechanisms are built upon the X Window client communications protocols. Therefore, each NExS connection client is also an X Window client (as is NExS and any other program which creates windows on your display). Connection programs are developed using the NExS Connection Library, which is a set of C and FORTRAN callable procedures that establish and maintain connections to an NExS spreadsheet running on your display, and provide all the functionality described above.

  Each NExS spreadsheet has 63 connection ports through which up to 63 independent NExS connection clients may attach to the spreadsheet. The NExS connection library provides "on the fly" double precision floating point and integer format conversions so that simultaneous NExS connections to machines with different architectures is possible. Once attached to a port, each NExS connection client may establish any number of its own menus, buttons, and extrinsic functions.

A useful analogy for understanding how NExS connections work is to think of the connection ports as slots in the back of a PC. Binding a connection program to an NExS connection port is like plugging an new board into an empty slot on the PC. Just as the new board's hardware becomes and extension of the functionality of the PC, the software procedures in a connection client become extensions of the functionality of NExS. Just as you can add more boards to a PC until you fill up all the slots, you can start up more connection programs until you use up all the ports.

NExS even allows you to disconnect and re-establish connections while it is running. (This is analogous to unplugging boards and plugging in new ones while the PC is powered up and running; generally not a good idea!) The X-Window server on your workstation acts as the "bus" over which all transactions between NExS and its connection clients take place.

It is possible to simultaneously run multiple copies of NExS on your workstation. To solve the problem of which instance of NExS a client program should connect to, the X-Window selection mechanism is utilized. This mechanism guarantees that no more than one instance of NExS on a given display can accept new connections at any given point in time. You have control over which instance of NExS is currently accepting connections as described in the next section.

An NExS spreadsheet can accept real-time data transfer from other applications anywhere in the world, as long as they can be linked to NExS through the X Windows communication mechanisms. Because NExS connections use X Window client message protocols, they work on any network that supports X Window protocols.

To create a client application that uses the NExS connection library, you must have a compiler for your development language and the X11 object library (libX11, release 3 or higher).

The NExS connection API library functions are described in detail in the electronic documentation included with NExS. See the Installation and Release Notes included with your distribution for the name and location of API documentation.

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NExS User's Guide, Version 1.3
XESS Corporation
31 December 1996