Small feedback, rather than AttributeDescriptor - please use Name.
The difference is the split between Query Model (Name), Metadata Model
(AttributeDescriptor) and Data Model (Feature).
These form three sides of a triangle - AttributeDescriptor needs to
describe the data well enough that the user can perform a query using the
appropriate Name. The query (using Name) can then be used to fetch the data
(in the form of Features).
I only know this as the first cut of the GeoTools feature model supported
query using AttributeType and it was horrible.
Jody Garnett
On Tue, Sep 16, 2014 at 5:53 AM, Falko Bräutigam <fa...@polymap.de> wrote:
> Thanks Jody, for your reply.
>
> I would raise a bug but currently I'm still trying to figure the ideas
> behind
> the API. To get things going I make a proposal about API changes. The idea
> is
> not to actually change things but to have something to discuss about.
>
> ----
> So, basic idea of my proposal is to have an explicite and clear
> create-modify-update API.
>
> Currently the *FeatureStore* looks like this:
>
> public interface FeatureStore extends FeatureSource {
> ... addFeatures(FeatureCollection<T, F> collection) ...
> ... modifyFeatures(AttributeDescriptor[], Object[], Filter) ...
> }
>
> These are different concepts to create(add) and to modify features.
> addFeature()
> forces the store to take an ordinary Feature and translate it into
> whatever the
> backend needs to create all of its properties. In contrast to
> modifyFeature()
> which works on property level and so leaves this responsibility to the
> client
> programm.
>
> Consider the following:
>
> public interface FeatureStore extends FeatureSource {
> /**
> * Creates a new feature in this store.
> *
> * @param id Feature id, or null.
> * @param initializer Functor that allows to init non-nillable
> values.
> */
> Feature createFeature(id, initializer) throws ...
>
> /**
> * Modifies the given Features.
> *
> * @throws IOException If feature does not exist.
> */
> void updateFeatures(FeatureCollection collection) throws ...
> }
>
> Foremost this delegates the problem of identifying complex/collection
> properties
> to the store (which is a good idea IMO). Besides it is symmetric between
> create
> and update. And it is easier(?) to use for the client.
>
> Likewise *Feature* (ComplexAttribute):
>
> public interface ComplexAttribute extends Attribute {
> /**
> * Creates a Property for the given name.
> *
> * @param initializer Functor that allows to init non-nillable
> values.
> * @throws IllegalArgumentException If 'maxoccurs' exceeded.
> * @throws IllegalArgumentException If the name does not exists
> in the
> * FeatureType.
> */
> createProperty(Name name, Initializer initializer);
>
> /**
> *
> * @return The collection of properties which match the specified
> name,
> * or an empty collection if no such properties match.
> * @throws IllegalArgumentException If the name does not exists
> in the
> * FeatureType.
> */
> getProperties(Name);
>
> /**
> *
> * @return The value of this property, or null!!!
> * or an empty collection if no such properties match.
> * @throws IllegalArgumentException If the name does not exists
> in the
> * FeatureType.
> */
> getProperty(Name);
> }
>
> Now there is a clear factory for properties. This allows to let
> getProperty()
> return null if its value is null (not-initialized).
>
> Ideas:
>
> - Semantic of methods is clear for both primitive and complex values. All
> the
> questions about semantic and how to work with complex features are solved
> with
> this API.
>
> - Creating a Feature in the store is very similar to creating a
> ComplexAttribute
> member inside the Feature. Easier to work with.
>
> - Having the Store being the factory of Features and ComplexAttributes
> makes it
> much easier to use store dependent Feature implementations. Very important
> IMO.
>
> - Droping addFeature() in favour of create/modify gives the programmer a
> better
> idea of the identity of a feature. addFeature() sounds like one can
> transfer a
> feature from store A into store B - which is not true as ID changes in
> almost
> all cases.
>
> Jody and all, it would be really great if you could check this, comment
> and/or
> complain mistakes and/or any misunderstanding of the API.
>
> Thanks!
>
> -Falko
>
> Am 12.09.2014 09:07, schrieb Jody Garnett:
> >
> > maybe and hopefully someone can help me with the following questions
> regarding
> > complex features and properties.
> >
> > Question: What is the semantic of: feature.getProperty("foo") ==
> null ?
> >
> > 1.: the property is not initialized
> > 2.: the property is not initialized *or* it does not exist in the
> type at all
> >
> >
> > If the property did not exist ... it would not be there. The fact that
> you see a
> > property (with a null value) probably indicates something like
> > <foo/> is present in the XML. You could consider that significant for
> your
> > application? I am not sure ...
> >
> > Keep in mind that not a lot of people do this stuff yet (most of use use
> simple
> > features) - and thus you may find our library inconsistent with the GML
> > specification (if so raise a bug) or inconsistent with itself (if so
> raise a bug!).
>
> --
> Falko Bräutigam
> http://polymap.org/polymap3
>
>
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