Re: [Geotools-gt2-users] Types vs. Descriptors

[Tim S. <tim...@ty...>]

On Wed, 2008-06-25 at 17:00 +0200, Adrian Custer wrote:
> Ah, yes, the suffering of the new feature module.
> 
> It is indeed a royal mess because of the need to be backward compatible.
> One of the first big pushes of the 2.6 branch will have to be to clean
> up the feature model by dropping all the deprecated classes. Last time I
> tried to sort trough things, I gave up even trying to align the javadocs
> until we could drop those deprecated classes and have at least some
> clarity.
> 
> The javadoc in GeoAPI is the closest to correct, so I would start there.
>

Unfortunately, the GeoAPI Javadoc doesn't provide much enlightenment in
this regard. Everything is expressed in terms of everything else, and
there's no high-level description available.

A sampling:

AttributeDescriptor -- Describes an instance of an attribute
Attribute -- An extension of Property for an attribute
Property -- An instance of a PropertyType
PropertyType -- The type of a property

These kind of circular definitions abound.


It seems to me, so far, that the descriptor is a more specific
description of how a property is used. That is, it includes the context
in which the property applies. (i.e. a particular type of feature will
have between two and five values of this property, and nulls are not
allowed. Another type of feature will have zero or one values for this
property, and nulls are allowed.)

The type, then, applies globally to a property, and the restrictions
specified there apply no matter what type of feature has that property.
It includes things like what types of values it can take (numbers,
dates, strings, etc.) and what the range of valid values is.

Is any of this on the right track?

I still can't figure out what the difference between a property and an
attribute is. Also, none of this resolves the methods that
PropertyDescriptor and PropertyType (and by extension
AttributeDescriptor and AttributeType) have in common, such as getName()
and getUserData(). Also, what is an abstract property type?

Finally, is AttributeDescriptor.getLocalName() intended to return the
same thing as AttributeDescriptor.getName().getLocalPart() or
AttributeDescriptor.getType().getName().getLocalPart()?


>
> Also you should try to find the latest publically avaiable draft of ISO
> 10109 to get some UML diagrams for what is going on and then keep
> falling back on "what XML would do" to figure your way through.
> 

What is ISO 10109? A Google search comes back with: ISO 10109-8:2005, 
Optics and Photonics, but that can't be right.


>
> --adrian
> 

Thanks,



Tim Swanson 
Software Engineer


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