XML-schema 'best practice' question

Lorenzo Gatti gatti at dsdata.it
Sat Sep 20 18:03:30 CEST 2008

On 20 Set, 07:59, Frank Millman <fr... at chagford.com> wrote:

> I want to introduce an element of workflow management (aka Business
> Process Management) into the business/accounting system I am
> developing. I used google to try to find out what the current state of
> the art is. After several months of very confusing research, this is
> the present situation, as best as I can figure it out.

What is the state of the art of existing, working software? Can you
leverage it instead of starting from scratch? For example, the
existing functionality of your accounting software can be reorganized
as a suite of components, web services etc. that can be embedded in
workflow definitions, and/or executing a workflow engine can become a
command in your application.

> There is an OMG spec called BPMN, for Business Process Modeling
> Notation. It provides a graphical notation
> there is no standard way
> of exchanging a diagram between different vendors, or of using it as
> input to a workflow engine.

So BPMN is mere theory. This "spec" might be a reference for
evaluating actual systems, but not a standard itself.

> There is an OASIS spec called WS-BPEL, for Web Services Business
> Process Execution Language. It defines a language for specifying
> business process behavior based on Web Services. This does have a
> formal xml-based specification. However, it only covers processes
> invoked via web services - it does not cover workflow-type processes
> within an organisation. To try to fill this gap, a few vendors got
> together and submitted a draft specification called BPEL4People. This
> proposes a series of extensions to the WS-BPEL spec. It is still at
> the evaluation stage.

Some customers pay good money for buzzword compliance, but are you
sure you want to be so bleeding edge that you care not only for WS-
something specifications, but for "evaluation stage" ones?

There is no need to wait for BPEL4People before designing workflow
systems with human editing, approval, etc.
Try looking into case studies of how BPEL is actually used in

> The BPMN spec includes a section which attempts to provide a mapping
> between BPMN and BPEL, but the authors state that there are areas of
> incompatibility, so it is not a perfect mapping.

Don't worry, BPMN does not exist: there is no incompatibility.
On the other hand, comparing and understanding BPMN and BPEL might
reveal different purposes and weaknesses between the two systems and
help you distinguish what you need, what would be cool and what is
only a bad idea or a speculation.

> Eventually I would like to make sense of all this, but for now I want
> to focus on BPMN, and ignore BPEL. I can use wxPython to design a BPMN
> diagram, but I have to invent my own method of serialising it so that
> I can use it to drive the business process. For good or ill, I decided
> to use xml, as it seems to offer the best chance of keeping up with
> the various specifications as they evolve.

If you mean to use workflow architectures to add value to your
business and accounting software, your priority should be executing
workflows, not editing workflow diagrams (which are a useful but
unnecessary user interface layer over the actual workflow engine);
making your diagrams and definitions compliant with volatile and
unproven specifications should come a distant last.

> I don't know if this is of any interest to anyone, but it was
> therapeutic for me to try to organise my thoughts and get them down on
> paper. I am not expecting any comments, but if anyone has any thoughts
> to toss in, I will read them with interest.

1) There are a number of open-source or affordable workflow engines,
mostly BPEL-compliant and written in Java; they should be more useful
than reinventing the wheel.

2) With a good XML editor you can produce the workflow definitions,
BPEL or otherwise, that your workflow engine needs, and leave the
interactive diagram editor for a phase 2 that might not necessarily
come; text editing might be convenient enough for your users, and for
graphical output something simpler than an editor (e.g a Graphviz
exporter) might be enough.

3) Maybe workflow processing can grow inside your existing accounting
application without the sort of "big bang" redesign you seem to be
planning; chances are that the needed objects are already in place and
you only need to make workflow more explicit and add appropriate new

Lorenzo Gatti

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