[Zope3-dev] Properties?

[Jim Fulton]

Zope 2 has a simple mechanism for extending the schema of many
standard objects, especially folders, with properties.  Properties
defined on folders and other objects provide additional attributes.
This makes properties easy to access.  This model has provided a
number of advantages:

- It has enabled the use of folders and documents as one-off
   isntances.

- It, together with acquisition, has made it easy to define and share
   simple variables/configuration data.

I think that this model has been pretty sucessful.

In Zope 2, this model was extended to support multiple property sheets
in two ways:

- ZClasses provide a somewhat convoluted mechanism that supports
   multiple collections of properties.

- WebDAV organizes properties into separate XML namespaces.

I suggest that something like this would be useful for Zope 3.
Note that these properties would straddle the line between data and
meta data.  They would be used as extended data, rather than as meta
data even though object implementations would be unaware of them.
(Really, by my definition that I have in an earlier post, they are meta
data, because object implementations don't use the data.)

What do people think about this? Is there agreement that we need
something like this? Is there agreement that the one-off instance
model of Zope 2 is worth preserving? I know I do.

Jim

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