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Re: Re[2]: [higgins-dev] IdAS: One attribute per type per DS
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Paul,
To have a single Attribute with multiple values is the same as to have a
list of attibutes with single value. However I prefer to have a list of
Attributes with single value by the following reasons:
1. We will need to make MUCH LESS changes to exist CP implementations (at
least for Jena CP).
2. We will not need to change IFilter interfaces (it is already implemented
for Jena CP).
3. I think it is not a good idea to move IHasMetadata from IAttribute to
ISimpleValue. IHasMetadata depends on used schema, and I think it is not
useful for BasicSimpleValues to implement this interface.
4. The problem of multiple Attributes is the same as the problem of multiple
values and will be resolved in the same way ( perhaps we need to replace
getAttribute(URI type) with getAttributes(URI type) for IDigitalSubject).
Thanks,
Sergey Lyakhov
----- Original Message -----
From: "Paul Trevithick" <paul@xxxxxxxxxxxxxxxxx>
To: "'Higgins (Trust Framework) Project developer discussions'"
<higgins-dev@xxxxxxxxxxx>
Sent: Saturday, April 28, 2007 8:55 PM
Subject: RE: Re[2]: [higgins-dev] IdAS: One attribute per type per DS
Valery wrote:
1) From HOWL POV I do not see a way to allow metadata on both
attribute and value level - we can have them at either attribute or
value but not on both.
1/2 of the problem is IS solved: We know how to have arbitrary metadata on a
higgins:Attribute (soon to be renamed higgins:ValueWithMetadata (note the
singular use of Value)), and, if we use N higgins:attribute predicates to
point to N higgins:ValueWithMetadata instances we have the underlying
representation, that, when surfaced at the IdAS API is presented as "one
attribute per type with N values each of which N values can have arbitrary
metadata".
1/2 of the problem that is not solved: With the above approach Valery is
correct that we don't yet have a design for associating metadata with the
entire SET of the N values mentioned above. We need to work on this.
<snip>
In case of our favourite person-with-address.owl
example we can't put metadata on sub-values (pwa:state, pwa:country,
etc) of complex value (pwa:postalAddress).
This is true. But I think we can live with this. Certainly for the immediate
present. If one needs to associate metadata at a more granular level, one
needs to not use Complex value types, but instead compose them from more
atomic objects using some (as yet undefined) collection classes. This also
needs design work.
Valery
> So, my understanding is that there are these remaining issue:
>
>
>
> 1) Making sure we agree on how the Jean CP maps from the IdAS APIs to
the HOWL.
>
> 2) agreeing to allow/disallow metadata at the value level in the IdAS
APIs.
>
>
>
> On #2, I don't remember anyone saying disallow.
>
>
>
> I propose the following:
>
>
>
> a) Continue to allow metadata on IAttribute (this allows for the
> point below that Paul says IS important)
>
> b) Re-adjust the APIs to reflect the notion of one attribute per type
>
> b.1) This consists of removing the metadata arg from
> IHasAttributes.getAttribute(URI attrID, Iterator metadata)
>
> c) Make IPropertyValue extend IHasMetadata
>
>
>
> Jim
>
>>>> "Paul Trevithick" <paul@xxxxxxxxxxxxxxxxx> 4/27/07 10:05 AM >>>
> Jim wrote:
>>
>> >>> Valery Kokhan <vkokhan@xxxxxxxxxxxxxx> 4/27/07 9:22 AM >>>
>> >Jim,
>> >
>> >As I can remember our original assumption was that main difference
>> >between attributes and values is that attributes *can* hold metadatas
>> >while values *can not*. Regardless from the fact that I do not see any
>> >way to model metadata on values using .owl I believe that our original
>> >assumption was 100% correct and just leave it at this.
>> >
>> >Now about multiple attributes of the same type on any digital subject.
>> >
>> >Take into consideration above assumption I personally believe that on
>> >API level we should allow both approach: multiple attributes of the
>> >same type and multiple values in single attribute.
>>
>> So, historically at first the API allowed one attribute per type. Then
we
>> decided we needed to allow metadata to differ on same-typed attributes,
>> and thus introduced the ability to have multiple attributes per type.
>> This led to much confusion and rendered the
IDigitalSubject.getAttribute
>> method fairly useless. Why? Because now we have to indicate the
>> attribute's type along with all it's metadata to distinguish it from
other
>> attributes of the same type. Otherwise, which occurrence of that
attribute
>> should the CP return?
>>
>> So, a couple of phone calls ago, we agreed to revert back to allowing
only
>> one attribute per type, and at that time I believe we decided to allow
>> metadata to be placed on values.
> Which aligns perfectly with higgins.owl. [As I mentioned I propose we
rename
> higgins:Attribute to higgins:ValueWithMetadata.]
> What Jim is proposing is allowing only one attribute per type. Which
could
> be fine and convenient from the IdAS POV. It is handled (as always) from
the
> HOWL POV using multiple higgins:attributes each with ONE value and each
> value with some optional metadata.
>>
>> >As a use case for multiple attributes of the same type I'd consider
>> >attribute like "relationship" where we need to keep track of when or
>> >by whom each particular relationship was created or modified.
>>
>> In this case, we could put the metadata on the values.
> Correct. And in HOWL each SubjectRelationship instance (the "value") has
its
> its own metadata. We're aligned.
>>
>> >As a use case for multiple values in single attribute I see attribute
>> >like "favoriteDrinks" where we don't care of when each particular
>> >value was modified by still want to know when entire list was changed.
>> <snip>
> Jim, this/Valery's use case IS important. We need the ability to put
> metadata (e.g. timestamp of when the list was changed) on the entire
list of
> values.
> I'll leave it to you to consider the IdAS API POV.
> But from the HOWL POV perhaps we could introduce Lists as first class
> objects and solve the problem that way? We'd still have one attribute
per
> type, but the value might be a List (List of values). This List could
itself
> have metadata on it.
> This would involve changing the HOWL to introduce a few new collection
> classes, like say, higgins:List, higgins:Set, etc. A List, for example,
> would be a kind of higgins:Attribute [what I'd prefer to call
> higgins:ValueWithMetadata]). I have to think about it some more, but it
> might be workable.
> _______________________________________________
> higgins-dev mailing list
> higgins-dev@xxxxxxxxxxx
> https://dev.eclipse.org/mailman/listinfo/higgins-dev
>
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