[higgins-dev] Re: IdAS questions

["Jim Sermersheim" <jimse@xxxxxxxxxx>]

Good points Sergey.  IMO, the update methods have not yet been very well thought out because we haven't had implementation experience yet.  
 
Responses inline

>>> "Sergey Lyakhov" <slyakhov@xxxxxxxxxxxxxx> 11/1/06 6:22 AM >>>
>Hello Jim,
>
>There are some questions about IdAS:
>
>1. The method Context.createSubject(URI subjectType, Iterable<IAttribute>
>attributes)
>requires a list of attributes. Is there any sense to pass a list of
>attributes to this method? In other words do we always have a set of
>attributes when we create new DigitalSubject and where we could get
>them if there is only one method to create an attribute in the IDAS API
>DigitalSubject.createAttribute()?

I can imagine there being two modes in which DigitalSubjects are created: 1) where the IdAS consumer is able to build the attributes itself (perhaps using BasicAttribute), and 2) where it needs to use methods from the CP to assist in building them.
 
You're right, we need to both a) allow the attributes parameter to be null, and b) provide a method by which the consumer can get an attribute for the subject being built.
 
It seems like what the IdAS user really needs is a way to first get an IDigitalSubject instance (which has not yet been added to the context), then from that the user can get IAttribute instances which are valid for that Digital Subject. Finally, once the Digital Subject has been populated with the desired and required attributes, it could be committed/added to the context.
 
The current IContext.createSubject is documented to also add the created Digital Subject to the context.  I propose we change the doc such that this does not happen, and that the user has to call a new addSubject method after populating the DigitalSubject.  When this was first proposed (at a F2F), there was some argument against it.  Some felt that this would allow any DigitalSubject (possibly from another Context) to be added, and that this was undesirable.  I don't see there being a way to protect against that, and I think the problems that might arise are something the CP can deal with.

>2. What is be presumed behavior of
>IHasAttributes.addAttribute(IAttribute attribute)? Should it create a
>new Atribute ontology instance and just copy value(s) of passed
>attribute to the newly created attribute, or it should set passed
>Attribute as a value? In other words can two DigitalSubjects refers to
>the same Attribute instance(as an ontology instance)? The same
>question is for method IHasMetadata.addMetadata(IMetadata metadata)
>and IHasProperties.addProperty(IProperty property).

I think this question has to be answered by each CP.  I don't think there's anything in the data model which would prevent two Digital Subjects from referring to the same attribute instance (in the ontology), so for providers which can benefit from this kind of modeling, it may make sense to implement it that way.  One note of caution:  When two DigitalSubjects point at the same attribute instance, modifying that attribute for one should probably not modify it for the other.  So there may be cases where the CP needs to create a new Attribute in order to cause a modification to work properly.
 
I'll try to think of some documentation to add to the IdAS interfaces to talk about this issue.

>3. IComplexValue extends IPropertyValue, however
>IPropertyValue.getData() has no any sense in case of IComplexValue.
>What should be returned by this method? Should it return
>Iterable<IProperty>?

I plan to remove this method as soon as we resolve the issue brought up in http://dev.eclipse.org/mhonarc/lists/higgins-dev/msg00694.html. For now, I suggest returning null.

>4. There are no interfaces ISimpleMetadata and IComplexMetadata in
>IdAS model looking at higgins ontology model such interfaces should be
>there.

Well, IMetadata is really just a marker -- it's really just an IProperty which produces IPropertyValues which are either ISimpleValue or IComplexValue.  Do you think this is an adequate analog to the ontology?  The other solution I see is to make IMetadata exactly like IProperty (and add IMetadataValue, IComplexMetadataValue and ISimpleMetadataValue), but this would all just be a replica of IProperty and make maintenance harder.
 

Jim