[okfn-discuss] CKAN and VDM

Mon Aug 10 16:57:03 UTC 2009

Not feeling very well so this will be brief ...

2009/8/9 James Casbon <casbon at gmail.com>:
> Hi Rufus,
>
> I'm trying to understand VDM on the way to understanding CKAN.
>  * Are there any docs that explain what is going on in general terms?

There's the main vdm package docstring:

<http://knowledgeforge.net/okfn/vdm/file/tip/vdm/__init__.py>

As that says at the top:

<quote>
Versioned Domain Model (vdm) is a package which allows you to 'version' your
domain model in the same way that source code version control systems such as
subversion allow you version your code. In particular, versioned domain model
versions a complete model and not just individual domain objects (for more on
this distinction see below).
<quote>

Any questions remaining after perusing that (and I'm sure there will
be :) !) let me know.

>  * I see you're using sqlalchemy migrate
> (http://www.rufuspollock.org/2009/07/27/sqlalchemy-migrate-with-pylons/)

We haven't actually transitioned to migrate yet though it is one of
our top tickets.

>  - am I right in thinking that migrate handles schema migrations,
> while vdm handles object versioning?

Exactly right.

>  * Have you seen this: http://code.google.com/p/django-rcsfield/

No. However, it looks rather different from vdm -- it seems to be
about versioning normal content *outside* of the DB using traditional
rcvs-es (if I have undestood correctly).

What I had seen was the versioning in elixir and the versioning plugin
for sqlobject. When I last looked at them (now a year or so ago)
neither of them full domain *model* versioning (they just versioned
individual objects via copy on write).

Rufus