[Zope-dev] Using Zope in a client-server system

[Michel Pelletier]

Itai Tavor wrote:
> 
> Hi,
> 
> I need to design sales center system containing a server and
> salesperson workstations. I thought it would be a good idea to build
> the system around Zope, for several reasons:
> 
> - With Zope on the server and a standard web browser on the
> workstations, a lot of low level work is already done for me and I
> can focus on high level issues such as UI and application logic.

Yup.

> - Easy connectivity to an SQL database.

Yup.

> - DTML code chunks and Python Methods should be easier to manage than
> 1000's of lines of Java or VB code.

Yup.

> - Easy to install and update the product and to manage and debug it
> through the web.

Yup.

> - It would be easy to create new ways to view the data - for example,
> a WAP version to send sales statistics to managers out of the office.

Yup.

> There are a couple of features that I am not sure how to implement though:
> 
> - I need to display constantly-updating information on the
> workstations. I could do this by reloading the window every second,
> but that seems ugly - I'd like to only update certain fields, which I
> can do using layers and JavaScript, but I need to get the updated
> data from the server. I guess that can be done with Java, but I'd
> like to keep the system simple - a browser with HTML and JavaScript
> only on the client side, DTML, Zope with Python Methods, and External
> Methods, and an SQL database on the server, no Java or any other
> complications.

Ah, well, you see you've hit one of the disadvantages of using a
stateless protocol like HTTP to solve your problem.  There is no good
general purpose solution that I know of to address this issue.

> - I also need to push data to the workstations - based on events
> detected at the server, I need to bring up a message on a
> workstation, and remove it in response to another event. I really
> don't want to refresh a frame every second for this, and I also would
> hate to have to write a Java applet to do it.

This is the identical problem to the one above.
 
> Any comments or suggestions regarding the above problems, the choice
> of Zope for this project, or the project in general would be
> appreciated.

If you want to go far enough, you can try and use XML-RPC (also,
stateless, but not client-bound to a certain model) and something like
wxPython to build your own GUI that can at least mantain some sort of
persistent or bi-directional communication between your clients and
servers.  But this is a big task.

I think if you maybe rethink your problem you can compromise on
something that does not require the server pushing data to the client.

-Michel