Hi Cees,
You may want to check out Smalltalk. Especially for an ERP solution I would not use Zope - ERP is lots of business logic, and I have tried three different ways of doing lots of business logic with Zope, and no one is satisfying. What about the GUI? Does it user standard browser technology or some client software? Is there any tool that assist the creation of GUI screens/pages? What's about Web publishing / applications server? What's about the object store?
For lots of business logic, if you want to stick with Python, I would recommend WebWare which has a more "classical" setup, with Python Server Pages and Servlets serving your users (PSP being the "View" and Servlets often acting as the "Controller"), and raw Python code containing the logic (the "Model" part of the picture). It has lots of bells and whistles in the latest version, among others an object-relational mapping layer (no OQL though).
I should have a look soon.
If you're not married to Python, I'd seriously consider Smalltalk. It's even more effective than Python, but one caveat is that certainly in the beginning you probably want an experienced Smalltalk "coach" on your team. Coupling Smalltalk to eXtreme Programming practices will probably result in an ERP that easily outperforms SAP R/3 on most fronts ;-)
Still I'm not married to Python. But I like the language. I really don't know much about SAP R/3, but I found that it is very expensive to have a good SAP installation / configuration. The guys which customize it earn well. Also I found that we can compete easily with SAP in smaller business, e.g. 5-30 workstations. (We have some companies here which are not very satisfied with SAP, but this seems to be responsability of the company which is installing, configuring and customizing it.) Good abstractions make the code modular and the application feasable. Also we have about 130 tables, using good class abstraction could reduce them to the half. We have about 90 code-modules and more than tha half are libs (reusable for other projects), a lot very generic functions. I did all the programming and the most of the GUI designing myself. It took about 2 years, everything included. Out app is running at 12 customers. And it is the same application for everyone. Only print reports (invoice form, orders, etc.) are customized. There are really a lot features demanded by all customers, such that the possibility to attach whatever other document to standard documents handled in the app (invoice, delivery note, project, etc.) and incidence tracking (to study cost-benefit, you only have to track what activity (=article) have you done for which customer/project). I would like to write an Open Source ERP whith all the standard thinks (Selling (Orders, deliveries / invoices) / Buying (same)/ Accountig / Stock / Incident tracking and some workflow/approvement cycles). Also I think that business models in Europe are very similar. I would like to know something about TransWarp from Phillip Eby. Will this help developing apps faster?
(ok, I'm exagerating...) Perhaps not.... ;-)
Cees de Groot http://www.cdegroot.com <cg@cdegroot.com> Erny