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Subject: Re: [sdo] Re: Comments on Blaises Proposal


Hi Frank,
 
I have responded to your comments below:
 
[Frank] For your Example #2, below:

> Y --containment--> ADDRESS --containment --> EMPLOYEE

This would not be possible with your model because the EMPLOYEE -> ADDRESS
reference is also containment, so you could not have the Y-containment
reference also pointing to the ADDRESS (it breaks the
exclusivity/ownership rule of containment).
[Blaise]  The three examples from my previous email were meant to be seperate and distinct from each other.  The following rule always applies:  Types A & B may have containment properties to Type C, but instances of Type A & B may not share a reference to an instance of Type C through those containment properties.

[Frank]Also, you say:

> Your argument is that the Address type can not have the opposite
property to Employee be containment.  With this restriction in the
resulting XML employee data could not be nested within address data.

Why not? This is exactly how your algorithm serializes the non-containment
"contact" reference (from PhoneNumber to Employee) in Example #3 of your
proposal document. Your algorithm consolidates non-conainment references
and orphans. What's different about this case?
[Blaise]  The only place where non-containment and orphans can be consolidated is in the complex type corresponding to the root type (during schema generation).  I added the types X & Y into the example in an attempt to clarify this point.  The examples in the email below do not correspond to a different algorithm, they just have different root types. 
 
-Blaise
 
----- Original Message -----
From: "Frank Budinsky" <frankb@ca.ibm.com>
To: <sdo@lists.oasis-open.org>
Sent: Thursday, April 10, 2008 10:26 AM
Subject: Re: [sdo] Re: Comments on Blaises Proposal

Hi Blaise,

Maybe the light just hasn't gone on yet, but my head is really starting to
hurt :-)

For your Example #2, below:

> Y --containment--> ADDRESS --containment --> EMPLOYEE

This would not be possible with your model because the EMPLOYEE -> ADDRESS
reference is also containment, so you could not have the Y-containment
reference also pointing to the ADDRESS (it breaks the
exclusivity/ownership rule of containment).

Also, you say:

> Your argument is that the Address type can not have the opposite
property to Employee be containment.  With this restriction in the
resulting XML employee data could not be nested within address data.

Why not? This is exactly how your algorithm serializes the non-containment
"contact" reference (from PhoneNumber to Employee) in Example #3 of your
proposal document. Your algorithm consolidates non-conainment references
and orphans. What's different about this case?

Frank




"Blaise Doughan" <
blaise.doughan@oracle.com>
04/09/2008 04:52 PM

To
<
sdo@lists.oasis-open.org>
cc

Subject
Re: [sdo] Re: Comments on Blaises Proposal






Hi Frank.
 
To be clear my proposal asks that the following existing API all be
allowed to return true wrt the example model:
 
employeeType.getProperty("residence").isContainment() == true;
employeeType.getProperty("residence").getOpposite().isContainment() ==
true;
addressType.getProperty("resident").isContainment() == true;
addressType.getProperty("resident").getOpposite().isContainment() == true;
 
The above truly reflects the data sharing rules.  The data sharing rules
are very useful for determing how data can be written to XML, I will
demonstrate with the following examples.
 
Example #1
 
We all agree on employee having a containment relationship to address.
 
X --containment--> EMPLOYEE  --containment--> ADDRESS
 
<x>
    <employee>
        <address>...</address>
    </employee>
</x>
 
 
Example #2
 
My proposal allows the opposite property from Address to Employee to also
be containment.  Again containment refers to the data sharing rules. Using
the data sharing rules an Address object can be marshalled as follows.
 
Y --containment--> ADDRESS --containment --> EMPLOYEE
 
<y>
    <address>
        <employee>...</employee>
    </address>
</y>
 
 
Example #3
 
Your argument is that the Address type can not have the opposite property
to Employee be containment.  With this restriction in the resulting XML
employee data could not be nested within address data.  This also forces
employee to have a key that address can make use of to represent the
non-containment relationship.
 
Y --containment--> ADDRESS --non-containment --> EMPLOYEE
 
<y>
    <address employee="1">...</address>
    <employee id="1">...</employee>
</y>
 
 
The reason I am proposing that a property and its opposite property can be
containment is because it reflects the data sharing rules.  Data sharing
rules are useful because they allow a better XML representation.   Example
#2 is better than example #3 (as example #3 requires a key that truly
isn't necessary).
 
-Blaise
 
 
----- Original Message -----
From: "Frank Budinsky" <
frankb@ca.ibm.com>
To: <
sdo@lists.oasis-open.org>
Sent: Tuesday, April 08, 2008 9:14 PM
Subject: Re: [sdo] Re: Comments on Blaises Proposal

Hi Blaise,

You said:

> In the relational database example two tables that related to one
another because the primary key is also the foreign key would result in a
bidirectional containment relationship.

Absolutely, I agree, but a bidirectional containment relationship is a
containment reference in only one direction. The inverse of the
containment reference is NOT also a containment reference, it's an
explicit (named) "container" reference. Looking at your EMPLOYEE and
ADDRESS tables, it seems clear to me that the containment reference is
from Employee to Address. The ADDRESS table has a FK to the EMPLOYEE table

which says there is a 1-1 relationship where ADDRESSES can't exist without

a corresponding EMPLOYEE. Therefore, Employees would own Addresses in the
logical model. The "residence" containment reference is exactly what I
would expect, and that's even what you say on page 20. Now, I understand
that you can take this a step further (especially when you bring JPA into
the picture) to say that the logical model's reference is bidirectional
with an explicit inverse named "resident". But, that should be the end of
story - you've defined a bidirectional containment reference. What I don't

understand is why you need to take this a step further and also say that
you need a new kind of special relationship where both ends are
containment - "bi-containment" as opposed to "bi-directional containment".

That's the part I just don't understand, and it sounds like maybe others
are also confused by?

Frank




"Blaise Doughan" <
blaise.doughan@oracle.com>
04/08/2008 05:02 PM

To
<
sdo@lists.oasis-open.org>
cc

Subject
Re: [sdo] Re: Comments on Blaises Proposal






Hi Frank,
 
The proposal is based on the premise that it is a worthy endeavor to
derive SDO metadata from sources like (relational databases and JPA
entities) in addition to XML schema.  At this point I'm not 100% sure we
agree on this premise.
 
My document demonstrates that bi-directional containment relationships
exist in the world (atleast in relational databases and JPA), as such the
proposal introduces bi-directional containment to SDO.
 
I have responded to your points below:
 
[Frank]The EMOF definition is exactly the same except for the part about
bidirectional composition, which I think is conceptual nonsense and needs
to be removed from the proposal.
[Blaise] I do not agree that SDO containment equals the EMOF definition of

composition.  In my examples I have demonstrated that containment relates
to things like the JPA OneToOne and OneToMany mappings.  The JPA OneToOne
mapping is allowed to be bidirectional and is very useful.  I have also
demonstrated that the underlying database structure represents
bi-directional containment.  We can continue to debate the definition, but

I am more interested in what metadata you would like to see derived from
the examples I've provided in my proposal.
 
As soon as you allow containment on both
ends of an association, you're guaranteeing containment cycles. By
definition, A1.getContainer().getContainer() == A1. Are you proposing that


we remove the restriction about containment cycles?
[Blaise] Cycles between two objects should be allowed.
 
[Frank]Assuming A1 references
E1, what would A1.getRootObject() return - A1 or E1? What about
E1.getRootObject()? Why would introducing this kind of complexity be good
for SDO?
[Blaise] Assuming a bi-directional containment relationship between A1 and

E1, then E1.getRootObject() would return A1, and A1.getRootObject() would
return E1.  The benefit for SDO would be to represent metadata that came
from sources other that XML Schema.  Also the ability to generate per type

XML messages (That all conform to the same data sharing rules). Again
assuming that it is a worth while goal to generate SDO metadata from
sources like relational databases and JPA entities (useful for a DAS),
what metadata would you like to see generated?  Note that metadata derived

from XML schema would not result in any containment cycles.

[Frank]All this aside, I can't even see what criteria one would use for
deciding
to define such an association.
[Blaise] There are two examples in the document that demonstrate when this

applies.  In the relational database example two tables that related to
one another because the primary key is also the foreign key would result
in a bidirectional containment relationship.  Also in the JPA entity
example a bidirectional OneToOne relationship results in a bidirectional
containment relationship in SDO.
 
In fact, it seems to me that your algorithm
would produce the same results if only the residence reference was
containment (i.e., resident was non-containment). Your step #6 seems to be


the key. Couldn't a slightly different version of step #5 even do the same


thing if neither end of the association were containment, that is, if you
say that 1-1 non-containment references to orphans should serialize in
place? Even as it is, I think the algorithm would produce resonable
serializations, even if the residence-resident association was completely
non-containment.
[Blaise] It may be confusing because the object model is shallow and the
complex type for the root type is converting the reference relationships
to nested relationships, adding another object to the model might make
things clearer.
 
[Frank] I really can't see why we need to invent a new modeling
concept (bidirectional composition) for SDO - that would seem pretty
extreme to me.
[Blaise] I do not see the extreme aspect to this proposal.  None of the
APIs change, it simply allows the back pointer of a containment
relationship to be containment.  It's not a new modeling concept (JPA has
this), it's just new to SDO.
-Blaise
 
----- Original Message -----
From: "Frank Budinsky" <
frankb@ca.ibm.com>
To: <
sdo@lists.oasis-open.org>
Sent: Tuesday, April 08, 2008 3:51 PM
Subject: Re: [sdo] Re: Comments on Blaises Proposal

Hi Blaise,

The EMOF definition is exactly the same except for the part about
bidirectional composition, which I think is conceptual nonsense and needs
to be removed from the proposal. As soon as you allow containment on both
ends of an association, you're guaranteeing containment cycles. By
definition, A1.getContainer().getContainer() == A1. Are you proposing that


we remove the restriction about containment cycles? Assuming A1 references


E1, what would A1.getRootObject() return - A1 or E1? What about
E1.getRootObject()? Why would introducing this kind of complexity be good
for SDO?

All this aside, I can't even see what criteria one would use for deciding
to define such an association. In fact, it seems to me that your algorithm


would produce the same results if only the residence reference was
containment (i.e., resident was non-containment). Your step #6 seems to be


the key. Couldn't a slightly different version of step #5 even do the same


thing if neither end of the association were containment, that is, if you
say that 1-1 non-containment references to orphans should serialize in
place? Even as it is, I think the algorithm would produce resonable
serializations, even if the residence-resident association was completely
non-containment. I really can't see why we need to invent a new modeling
concept (bidirectional composition) for SDO - that would seem pretty
extreme to me.

Frank




"Blaise Doughan" <
blaise.doughan@Oracle.com>
04/08/2008 09:45 AM

To
<
sdo@lists.oasis-open.org>
cc

Subject
Re: [sdo] Re: Comments on Blaises Proposal






Hi Frank,

If the definition I'm proposing for containment matches the one in EMOF
that
is great.  Containment is referred to many times in the SDO spec and
factors
into many aspects, so I feel there is value in defining it in the SDO
spec.
If the EMOF definition of composition implies a "part-of" relationship in
which a bidirectional composition relationship is not allowed then my
definition is new and different since it would allow this.

You are correct in that the only possible bi-directional relationship with



containment in both directions is a 1-1. This type of relationship is not
uncommon in relational databases and is well supported by JPA.

-Blaise

----- Original Message -----
From: "Frank Budinsky" <
frankb@ca.ibm.com>
To: <
sdo@lists.oasis-open.org>
Sent: Monday, April 07, 2008 5:14 PM
Subject: Re: [sdo] Re: Comments on Blaises Proposal


Hi Blaise,

> 1.  A clear definition of what containment is:

I think the definition is very clear already. As you pointed out, the spec
currently says that containment is the same as EMOF composition. This is a
well known concept, the same concept as UML bi-value aggregation, as I
said below. Your clarification isn't saying anything new or different.

> 3.  Allowing both properties involved in a bidirectional relationship to
be containment=true.

Unless I've missed something, this doesn't work for anything but 1-1
relationships. Assume you have A1 with "resident" (containment) references
to E1 and E2. If you also say the E1 to A1 reference ("residence") is a
containment reference, rule #1 is already broken (because E2 is also
pointing at A1).

What am I missing here?

Frank.




"Blaise Doughan" <
blaise.doughan@oracle.com>
04/07/2008 11:19 AM

To
<
sdo@lists.oasis-open.org>
cc

Subject
Re: [sdo] Re: Comments on Blaises Proposal






Hi Frank,

My proposal contains small changes with a big impact:
Clear means of deriving metadata from sources such as relational databases
and JPA entities.
Multiple compatible XML representations for SDO DataObjects:  If you
exposed your DAS through a web service you could define your underlying
model once and have per type XML messages (see the proposal for examples
of this).
Full backwards compatibility.

What is being proposed is the following:

1.  A clear definition of what containment is:
"For a property representing a relationship between two types A and B,
then the property is considered containment if instances of Type A may not
share instances of Type B.  In addition Type C may have a containment
relationship to Type B, but an instance of A and an instance of C may not
both reference the same instance of B through containment relationships."
2.  Removing the restriction that each data object must be reachable by
containment.  This requirement is directly related to the XML
representation and this is why the proposal contains a modified algorithm
for converting DataObjects to XML.
3.  Allowing both properties involved in a bi-directional relationship to
be containment=true.  This is required when deriving metadata from sources
other than XML schema.


Below are my responses to your email:

[SAP1] How does this differ from the UML concept of aggregation.
[Blaise-08/04/03] I guess this depends on your definition of aggregation
in UML.  The following is the important concept:
    Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can never be true
    Non-Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can be true
[Frank] My ("the") definition of UML aggregation is "a has-a (whole/part)
relationship".
[Blaise-08/04/07] My hope was to just use a UML word like aggregation or
composition and found it to imprecise.  Martin Fowler once wrote,
"Aggregation is a part-of relationship.  It's like saying that a car has
an engine and wheels as its parts.  This sounds good, but the difficult
thing is considering what the difference is between aggregation and
association".  And according to Martin Fowler, Jim Rumbaugh has the
following to say about aggregation, "Think of it as a modeling placebo".

[Frank]Aggregations can either be shared (i.e., a part can be used in more
than one aggregations) or exclusive (also known as by-value aggregation or
composition). SDO containment is the latter (exclusive aggregation); a
part can be used in only one aggregation/container - which is returned by
the getContainer() method. Blaise's definition, above, seems to be the
same thing. If so, what exactly is the proposed containment change?
[Blaise-08/04/07] The SDO 2.1 spec does not clearly define what a
containment relationship means.  In section "3.6.3 Containment" it comes
close by stating the corresponding term in EMOF is called "composite". See
my proposed definition of containment at the beginning of this email.

[Frank]The only thing that seems different (and very strange, in fact) is
the example of an association where both ends have containment=true.
Allowing this seems to be fundamentally at odds with the concept - i.e., a
part cannot contain its whole.
[Blaise-08/04/07]  According to my definition above both ends of a
containment relationship may have containment=true.  I could not find the
following requirement related to containment in the SDO 2.1 specification:
"a part cannot contain its whole".

[Frank]How would we know which is the whole and which is the part, given
both can be either according to the metadata?
[Blaise-08/04/07] My proposal includes an example of deriving metadata
from a relational database.  There is a relationship formed between the
EMPLOYEE and ADDRESS tables, since they relate to each other by having the
same primary key values.  In this example we know for each employee there
is a unique address, and for each address there is a unique employee.
There is no way to know which one is the whole and which is the part.

Sounds like you want some new kind of bidirectional relationship that says
one end or the other is containment, but the metadata won't say which end.
Is that it? If so, how would the DataObject.getContainer() method work?
[Blaise-08/04/07]  There is no need for a new kind of bidirectional
relationship, my proposal is to allow the opposite property to be a
containment relationship.  getContainer() continues to work as it does
today.  In my particular example for the relationship between Employee and
Address:  getContainer for instances of Employee would return an instance
of Address, and getContainer for instances of Address would return an
instance of Employee:
DataObject anAddressDO = anEmployee.get("residence");
anAddress == anEmployee.getContainer();  // return true
anEmployee == anAddress.getContainer();  // return true

[Frank]Thanks, Frank.
-Blaise


----- Original Message -----
From: "Frank Budinsky" <
frankb@ca.ibm.com>
To: <
sdo@lists.oasis-open.org>
Sent: Monday, April 07, 2008 12:00 AM
Subject: Re: [sdo] Re: Comments on Blaises Proposal

Hi Guys,

I like the proposed mapping to XSD for models that don't have containment
references. However, that said, I really don't understand what change is
being proposed for containment here. I think I need a better answer to
Ron's question from below:

[SAP1] How does this differ from the UML concept of aggregation.
[Blaise] I guess this depends on your definition of aggregation in UML.
The following is the important concept:
    Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can never be true
    Non-Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can be true
[Frank] My ("the") definition of UML aggregation is "a has-a (whole/part)
relationship". Aggregations can either be shared (i.e., a part can be used

in more than one aggregations) or exclusive (also known as by-value
aggregation or composition). SDO containment is the latter (exclusive
aggregation); a part can be used in only one aggregation/container - which

is returned by the getContainer() method. Blaise's definition, above,
seems to be the same thing. If so, what exactly is the proposed
containment change? The only thing that seems different (and very strange,

in fact) is the example of an association where both ends have
containment=true. Allowing this seems to be fundamentally at odds with the

concept - i.e., a part cannot contain its whole. How would we know which
is the whole and which is the part, given both can be either according to
the metadata? Sounds like you want some new kind of bidirectional
relationship that says one end or the other is containment, but the
metadata won't say which end. Is that it? If so, how would the
DataObject.getContainer() method work?
Thanks, Frank.




"Blaise Doughan" <
blaise.doughan@oracle.com>
04/04/2008 11:14 AM

To
<
sdo@lists.oasis-open.org>
cc

Subject
[sdo] Re: Comments on Blaises Proposal






Hello All,

I think this is going to turn out to be a very good discussion on
containment :),


There are some points in the proposal I would like to draw attention to:

1. Full Backwards Compatibility
A number of TC members have made strong cases for backwards compatibility
and my proposal supports this.  A user defining SDO 2.1 compatible
metadata will not see any change in behaviour wrt my proposed changes.

2.  Relaxed Containment Requirements
The proposal allows for a data graph to have no containment relationships.

 This reflects the case where SDO metadata is derived from unannotated
Java classes/interfaces.  Since XML handling is a core part of the spec
(XMLHelper, XSDHelper, DataObject serialization), the proposal provides an

algorithm to keep these concepts valid.  Ron has pointed out that the
algorithm can fail, but it fails in the same way as all other XML binding
tools.  The alternative is to not allow the XML serialization of
DataObjects without all the necessary containment which is difficult to
determine and is unnecessarily restrictive.

3.  DAS
The proposal contains an example of deriving SDO metadata from a
relational database.  XML schemas are then derived wrt different SDO
types.  I am excited about the idea that the data source metadata could be

defined once, and then per type XML messages (one for findAddress, another

for findEmployee) could be used each of which reflects the core metadata.


Below are my responses to the points raised by Ron's email:

[Ron] Much as I like aspects of this proposal, there are several
fundamental problems with it.  In particular, Blaise's claim that "makes
use of containment properties when they are present and handles things
when they are not" is false.  The fundemtental problem is that what Blaise

calls "orphans" can not be determined by analysing the metadata, you have
to look at the actual instances.  Using the proposed algorithm, it is
still possible to generate documents with unresolved references.
[Blaise] I do not believe the claim is false.  Solving the object-to-XML
impedance mismatch requires that each object be reachable by containment,
the onus is always on the user to ensure enough containment relationships
are in place (this is true in both SDO 2.1 and JAXB 2.0).  The algorithm
could prevent all broken references by allowing remaining orphan instances

to be adopted by the complex type corresponding to the root type.  The
algorithm borrows from the "technical root" originally proposed by Xcalia,

but instead of requiring an additional object, the algorithm gives a place

for non-contained data to go.

[Ron] I want to point out that this, or any other proposal regarding
containment within a context is somewhat orthogonal to the issue 66. Issue

66 solves the more general problem of moving data between contexts in
which the definition of the types varies slightly.  Both containment and
instance class are our first targets, but certainly we believe this to be
a a way in which other problems, such as versioning, can be addressed.

[Ron] Nonetheless, let's compare, at a very high level, the approach to
containment of the two approaches.

[Ron] One of the problems we've got when dealing with different
application using different sources of metadata is that the definition
have to sync-up.  In standard SDO 2.1, metadata comes basically from XSD.
The standard defines how to convert this to Java, and it's expected that
the users of the java interfaces take what they get.

[Ron]Blaise's proposal at least allows a second route.  It allows the data

to be defined from Java, and any XML clients have to take what they get.
[Blaise] My proposal involves a reinterpretation of what containment
means.  In SDO 2.1 containment represented a nested relationship between
DataObjects.  A DataObject of Type A can be nested within a DataObject of
Type B in the resulting XML if an instance of Type A cannot be shared
between instances of Type B.  Containment in SDO 3.0 should not simply
represent nesting, but the underlying concept that enables nesting.  This
does not simply allow a "second route", but makes it easier to derive an
SDO metadata from multiple sources.  It is more useful for containment to
model the data sharing rules from a relational database or JPA entities,
then to be an artificial mapping of these sources to an XML schema.

[Ron]That we've tried to achieve with Issue 66 is to "meet-in-the-middle".

 That is, for instance, some aspects of the model can be defined in Java,
the things that effect XML can be defined in XSD.  Both sides can be kept
a little happy.
[Blaise]  The issue 66 proposal works well when the SDO model being
projected has no containment relationships and is projected into a context

with containment relationships.  This is a well proven approach
demonstrated by technologies such as JAXB and JPA.  It becomes more
difficult when projecting a model with containment to a model with
containment.

[Ron]In other words, the project method allows the XML structure to be
added in after the Properties are already defined, without touching the
application that is defining the properties.  None the less, the XML
client has a large degree of flexibility in defining the document he
wants.
[Blaise] A common TopLink/EclipseLink use case is the following.  A
programmer is creating an application to access relational data and expose

it as a web service (XML).  They create an object model and apply JPA
metadata in the form of annotations to map the objects to the database.
Now in order to map these same objects to XML the user needs to apply JAXB

annotations.  When I do this I always look at the JPA annotations to find
out the data sharing rules so I can apply containment/nesting
relationships.  There are N ways to map an object model to an XML schema,
when I take into account the data sharing rules from the JPA annotations
there are always <N ways to map the annotated object model to an XML
schema.  If SDO metadata evolves to represent real relationships between
data it can ease the transition from one form to another.


[Ron]Please find my detailed comments to Blaise's proposal in the attached

document.


Best Regards,
Ron


Responses to document comments:

[SAP1] How does this differ from the UML concept of aggregation.
[Blaise] I guess this depends on your definition of aggregation in UML.
The following is the important concept:
    Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can never be true
    Non-Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can be true

[SAP2] Address has ?eId?, is that because there is a 1:1 relationship
between employee and address.  But if that?s the case, I wouldn?t expect
an SDO representation to give them both keys, the reference to the ?main?
object should be enough?
[Blaise] The domain model used in this example was derived from a
relational database so I brought in all the primary keys.  If Address is
never used as a root type, and is only referenced through containment
relationships then it would not need an ID (to satisfy SDO).

[SAP3[You have a bi-directional relationship, that is containment in both
directions.  In 2.1 this is not allowed (since it would result in an
endless loop when serializing).  How would we ever find the ?root? of a
datagraph?  Would we have to check for cycles?
[Blaise] When generating an XML schema if the value of containment
property is being converted then the property representing the back
pointer to the parent must not generate an XML element.  Instead the XML
schema should be annotated to indicate that this relationship exists.

[SAP4]Wouldn?t it be possible to take the document structure you define
later and apply it here?  What would be the effect?  Would this be
equivalent to the transitive closure?  I?m asking because when we?re
coming from unannotated classes, there is default no containment, and
therefore no meaningful change summary.  It would be good if we could
apply your algorithm to solve this problem.
[Blaise]If the scope of ChangeSummary was changed from containment to the
datagraph itself then the document structure in the document would apply.

[SAP5]I like this.  But it?s rather besides the point for the containment
proposal, isn?t it.  Unless you require that all non-containment
properties have keys, which you?re not doing, right?
[Blaise] It is not the non-containment properties that keys but their
values.  This is particulary useful for SDO Types with composite keys.

[SAP6]It?s interesting that you have non-containment as the default case,
exactly the opposite of what JAXB does.  How does this proposal relate to
the topic of JAXB alignment.  Are we defining new annotations?
[Blaise] For the purpose of this document I kept the annotations strongly
linked to the Property metadata.  Since Property had a property called
"containment" I introduced an annotation called "Containment".  The
specifics of the annotations can be worked out as part of a seperate
discussion.

[SAP7]In your definition of containment, Address is exclusively owned by
employee, right?
[Blaise] Yes see my response to [SAP2].

[SAP8]In your example the traversal path is always clear, but I don?t
believe this is generally true.  Especially if we are coming from Java
interfaces, where the order of the properties is undefined.
[Blaise] The order of properties is unrelated to the traversal path.

[SAP9]I believe there is a conceptual problem here.  It is not Types that
are ?orphaned?, but objects.  A type could still have some containment
relationship to another type, but instances of that type used someplace
else, in a non-containment relationship.
[Blaise] In the SDO Type to XML Schema algorithm containment relationships

in SDO translate to nesting relationships in XML schema.  As such types
can definitely be orphaned, the solution to this is to have the complex
type corresponding to the root type "adopt them"  although this
relationship is represented in the XML schema it is never realized as a
property on the root type.  Instances can also be orphaned, the algorithm
makes the same assumption as SDO 2.1 and JAXB that all the necessary
containment relationships are in place, if this is not sufficient then the

root complex type will need to be adapted to always expect orphans.

[SAP10]I?m trying to imagine your use-case.  Is it something like this?
You have something like a DAS with methods like getAddress(),
getEmployee(), etc.  And even though the SDO representation of the results

are the same, you want to have a different schemas for each result type.
Is that correct?  This is an extremely cool idea!
[Blaise] That is the exact use case we have in mind. The core data model
is derived from the data source, then data is requested based on a
particular SDO type.  The XML representation of this data should have the
queried type as the root type.

[SAP11]Traversal path is not sufficiently defined.  It seems to mean, if
I?ve already seen the type, I don?t generate the element.  Is this right?
In your examples, every time a reference is thrown out based on this rule
it happens to be the back-pointer to a containment relation.  I agree that

in this case, we can throw the data out of the XML.  However, this does
not hold in general.
[Blaise] If the SDO type has already been seen and an XML complex type has

already been generated then don't generate another XML complex type for
it.  When converting properties to elements then if the property is
containment create a nested element, otherwise create an element
representing a FK.

Imagine a node that has a containment relationship to itself (say,
Person.children).  That?s of course, a trivial example, but you could have

more complex models, where this would be impossible to analyse.
[Blaise]Not sure if the answer to the above point addresses this, but a
SDO type can have a containment property of the same type as the owning
type.

I think this algorithm makes the fundamental mistake of thinking that
containment is a feature of the metadata, where it?s really a part of the
data.
[Blaise]  Can you comment further on containment being part of the data?

See also the following comments.
[SAP12]Lets imagine adding ?Department? to this model.  Department has a
relationship to Employee, and has a non-containement relationship to
address.
The type ?Address? won?t be an orphan, but the XML would contain
unresolved references.
[Blaise] See my response to [SAP13]

Maybe there should be a property ?orphans? that has type ?Object?, rather
than a set of elements?
[Blaise] During the marshalling process "orphans" can be determined, there

is no need to explicity track them as a property value.  Also the orphans
change depending on the type of the root object.

[SAP13]Same problem.  In a general case, the list of employees that is
property of this object might not be the complete list that you want to
have in your orphans.  In such cases, this  is broken.
[Blaise]  This algorithm does make the assumption that if there are
containment relationships defined for a SDO type then they will hold all
the instances that will be referenced by non-containment relationships.
This is assumption is also made by SDO 2.1 and JAXB 2.0.  This assumption
could be removed by adding elements to the root complex type to hold onto
all orphaned instances.

[SAP14]How do we know when to apply this algorithm, and when to apply the
algorithm specified in SDO 2.1?  I think there might be backwards
compatibility issues here.  Maybe we need a flag to determine this.
[Blaise] I do not see the algorithm specified here as being a second
algorithm.  Instead it is an ammendment to the 2.1 algorithm.  When
converting SDO 2.1 compliant metadata to XML schema the algorithm will
produce the same XML schema.  Of course the algorithm also supports the
proposed metadata.


 -Blaise

----- Original Message -----
From: "Barack, Ron" <
ron.barack@sap.com>
To: <
blaise.doughan@oracle.com>; <sdo@lists.oasis-open.org>
Sent: Thursday, April 03, 2008 6:22 PM
Subject: Comments on Blaises Proposal

Hi Everyone,

Much as I like aspects of this proposal, there are several fundamental
problems with it.  In particular, Blaise's claim that "makes use of
containment properties when they are present and handles things when they
are not" is false.  The fundemtental problem is that what Blaise calls
"orphans" can not be determined by analysing the metadata, you have to
look at the actual instances.  Using the proposed algorithm, it is still
possible to generate documents with unresolved references.

I want to point out that this, or any other proposal regarding containment

within a context is somewhat orthogonal to the issue 66.  Issue 66 solves
the more general problem of moving data between contexts in which the
definition of the types varies slightly.  Both containment and instance
class are our first targets, but certainly we believe this to be a a way
in which other problems, such as versioning, can be addressed.

Nonetheless, let's compare, at a very high level, the approach to
containment of the two approaches.

One of the problems we've got when dealing with different application
using different sources of metadata is that the definition have to
sync-up.  In standard SDO 2.1, metadata comes basically from XSD.  The
standard defines how to convert this to Java, and it's expected that the
users of the java interfaces take what they get.

Blaise's proposal at least allows a second route.  It allows the data to
be defined from Java, and any XML clients have to take what they get.

That we've tried to achieve with Issue 66 is to "meet-in-the-middle". That

is, for instance, some aspects of the model can be defined in Java, the
things that effect XML can be defined in XSD.  Both sides can be kept a
little happy.

In other words, the project method allows the XML structure to be added in

after the Properties are already defined, without touching the application

that is defining the properties.  None the less, the XML client has a
large degree of flexibility in defining the document he wants.

Please find my detailed comments to Blaise's proposal in the attached
document.


Best Regards,
Ron


-----Ursprüngliche Nachricht-----
Von:
blaise.doughan@oracle.com [mailto:blaise.doughan@oracle.com]
Gesendet: Donnerstag, 3. April 2008 22:05
An:
sdo@lists.oasis-open.org
Betreff: [sdo] Groups - Proposal - Containment and Enterprise Data Models
(SDO-EnterpriseDataModel.doc) uploaded

This is the containment proposal I mentioned during the conference call on
April 1, 2008.

 -- Mr. Blaise Doughan

The document named Proposal - Containment and Enterprise Data Models
(SDO-EnterpriseDataModel.doc) has been submitted by Mr. Blaise Doughan to
the OASIS Service Data Objects (SDO) TC document repository.

Document Description:
The SDO spec to date has primarily concerned itself with deriving SDO
metadata from XML schema.  As such containment has come to represent the
concept of nesting as it relates to XML elements.  We prefer to think of
containment as a type of "privately owned" concept.  For the association
"residence" between types "Employee" and "Address" if instances of
"Employee" may not share references to instances of "Address" then it is a
containment relationship:

Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");
 // This can never be true
Non-Containment:  employeeDO1.get("residence") ==
employeeDO2.get("residence");  // This can be true

Using the above interpretation of containment it becomes easy to derive
SDO
metadata from other sources, such as JPA entities, JAXB objects,
relational
databases, etc. (the doc provides an example of deriving SDO metadata from
a relational database).  These sources may not have a concept of nesting,
but they are aware of data sharing rules.  Of course DataObjects require
an
XML representation, and containment has been an important part of that.
The attached proposal contains an algorithm that makes use of containment
properties when they are present and handles things when they are not.

View Document Details:
http://www.oasis-open.org/apps/org/workgroup/sdo/document.php?document_id=27848






Download Document:
http://www.oasis-open.org/apps/org/workgroup/sdo/download.php/27848/SDO-EnterpriseDataModel.doc







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