Hi all,
I'm trying to get a conceptual understanding of what a ChangeSummary is
and what you can do with it. I hope this is a good place to discuss this.
This is what I think.
/// fairly sure about this
1. A DataGraph is a structured graph of DataObjects
2. A ChangeSummary gives me a list of all DataObjects from my DataGraph
that have changed (including created & deleted)
3. For each DataObject that has changed, I can see what properties have
changed and can access the old and new value
/// less sure
4. In case non-datatype properties have changed, the old value is the
reference the object had before change tracking started. The contents of
the DataObject that is referred to can have changed.
For instance suppose I have the graph containing three data objects (for
simplicity all of the same type):
A(name=a) -> B(name=b) -> C(name = c)
where arrows indicate non-datatype properties and name is a string
property. If this graph is changed into
A(name=a) -> C(name=cc) -> B(name = bb)
Then all three objects will have changed. For object A, one property has
changed: the reference (B -> C). If I ask the changesummary for the old
value of the reference I get a reference to B whose name is equal to bb.
This might seem a bit strange because in the old days, A referred to B
with name=b.
/// even less sure
5. Suppose I now want to make an update service that uses the
ChangeSummary to update my back-end datastore.
Then, the only way I can think of that makes ChangeSummary useful is
either when
1. I have implementation specific identifier properties are
associated with each type [for instance by giving each of my DataObject
types a URI property]
or
2. The structure of my DataGraph (i.e. the links between the
various DataObjects) can't change
Am I off track? Any comments welcome,
Bert
PS: I'm not always as clear as I want to be... so if I need to clarify
something, I'll be happy to!
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