I think we're getting somewhere here. I agree with all the views
you have in this reply except one...
>2. Attibute was returned by IDigitalSubject.getAttribute(). In this
case it
>is "stored" attribute and its value should be
changed.
I think it's too confusing to the IdAS consumer (and will also require
state tracking by the CP) to have two semantics associated with the same
method based on how the object was originally obtained. I would
rather see setValue only affect the in-memory copy of the Attribute.
In other words, think of IAttribute's returned by
IDigitalSubject.getAttribute as returned by value rather than returned by
reference (which would be more symmetric with the way you propose we think of
IAttributes which are passed to IContext.addSubject). If we do this, the
semantics of an IAttribute instance remain consistent.
In fact, it was this very issue which led me to push all build and update
methods to IContext and off of the specific objects. There was nothing
to indicate to the IdAS consumer when an update would actually change
something in a backing data store. For example, a complex application
might have a function which takes an IAttribute and at some point might call
setValue on it. That function might not know how the IAttribute was
obtained.
The only argument I see against this is one of convenience to the IdAS
consumer. Let's se what it would take to update an attribute once it has
been gotten from a subject:
There are a number of ways to make the 3 lines of code easier. We
could overload updateSubject to take a single UpdateOperation (but there is
another thread asking that we discontinue overloading). We could add more
methods like IContext.updateAddAttribute(String cuid, IAttribute attr) which
are really just shortcuts for the three lines above, but then we get method
bloat. I'm not sure those 3 lines of code are that bad.
>>> "Sergey Lyakhov" <slyakhov@xxxxxxxxxxxxxx> 3/28/07
8:49 AM >>>
Jim,
> // Next, I assume all would agree
that this would add the entire
> myAttribute to mySubject2
>
Vector v = new Vector();
> v.add(myAttribute);
> String s =
myContext.addSubject("http://...#person", "mySubject2", v,
>
null);
I think we should consider myAttribute as a parameter by value
not by
reference. For mySubject2 we should create its own attribute
instance, not
just set a reference to myAttribute. So there should not be
any two
DigitalSubjects which have a reference to the same attribute/value
instance.
> // Next, I assume all would agree that this would add
the entire
> myAttribute to mySubject2
> Vector v = new
Vector();
> v.add(myAttribute);
> String s =
myContext.addSubject("http://...#person", "mySubject2", v,
>
null);
> // Here's where I'm confused. Does this affect
mySubject1, mySubjet2,
> both, or neither?
>
myAttribute.setValue(buildSimpleValue("http://www.w3.org/2001/XMLSchema/normalizedString","brown"));
I
think we should separate two possible situations:
1. Attribute is
"in-memory" instance created by IContext.buildAttribute().
In this case
IAttribute.setValue() shouldn't cause any changes for
DigitalSubject. In
other words setValue() for "in-memory" attribute should
invoke only
"in-memory" changes for this attribute.
2. Attibute was returned by
IDigitalSubject.getAttribute(). In this case it
is "stored" attribute and
its value should be changed.
Thanks,
Sergey Lyakhov
-----
Original Message -----
From: "Jim Sermersheim"
<jimse@xxxxxxxxxx>
To: "'Higgins (Trust Framework) Project developer
discussions'"
<higgins-dev@xxxxxxxxxxx>
Sent: Wednesday, March
28, 2007 12:23 AM
Subject: [higgins-dev] Stored versus in-memory IProperty
instances (was:IdAS
is now Java 1.4)
>>> "Sergey
Lyakhov" <slyakhov@xxxxxxxxxxxxxx> 3/27/07 10:51 AM
>>>
<snip>
>I think we need to create a new
"stored" instance of IProperty for each
>stored Digital Subject
regardless of which type of IProperty ("stored" or
>"in-memory") was
passed to setValue(). In this case there will be no any
>two or more
Subjects which refers to the same "stored" instance of
>attribute,
metadata or value.
I'm trying to envision what this would look like.
Let's use some sample code
to talk about it:
IDigitalSubject
mySubject1 = myContext.getSubject("subject1");
IDigitalSubject mySubject2 =
myContext.getSubject("subject2");
IAttribute myAttribute =
mySubject1.getAttribute("eyeColor", null);
// At this point, is
myAttribute associated with MySubject1 in terms of
updates?
// In other
words what happens here, does it only affect the in-memory copy,
or does
it also affect mySubject1?
// I think you're opinion is that this should
affect
mySubject1.
myAttribute.setValue(buildSimpleValue("http://www.w3.org/2001/XMLSchema/normalizedString","blue"));
//
Next, I assume all would agree that this would add the entire myAttribute
to mySubject2
Vector v = new Vector();
v.add(myAttribute);
String
s = myContext.addSubject("http://...#person", "mySubject2", v,
null);
// Here's where I'm confused. Does this affect mySubject1,
mySubjet2, both,
or
neither?
myAttribute.setValue(buildSimpleValue("http://www.w3.org/2001/XMLSchema/normalizedString","brown"));
Jim
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