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Subject: TR: [sdo] Containment discussion
Hi, Due to OASIS membership issues, Xcalia members are temporarily unable to post messages on the SDO3 mailing list (and also unable to use their @xcalia.com on the SDO comment mailing list). Here the reply to the last mail from Blaise we've received. Thanks and sorry for the inconvenience, --François De : François Huaulmé Envoyé : jeudi 24 avril 2008 15:18 À : sdo@lists.oasis-open.org Objet : RE: [sdo] Containment discussion Hi, Here are some thoughts following last Blaise's mail. First, I'd like to ensure we're all talking about the same use case: • Containment is EMOF/UML aggregation • We have 2 types: A and B. • We have a "A –contains-> B" relationship • We'd like to see an instance of B (B1) as the "root" element of the serialized datagraph. • B1 is contained by an instance of A (A1). In this use case, B1 needs A1 somewhere in the serialized datagraph. Speaking from a DAS point of view, B1 might not have any "identity" but its container (A1). If a DAS wants to update values of B1, it needs A1 because there might be no way to find B1 without its container, A1. A simple way to express aggregation using XML is to nest the aggregated object/elements as children of another element/object. So, if I follow the Oracle's proposal and if I start from B1 then I'll get a XML that would look like this: <B name="B1"> <A name="A1"></A> </B> The generated schema will inform that the nested A1 is the actual container of B1 using a "sdo:oppositeProperty" (Blaise: I'm having trouble with the Oasis web site so I could not download the last version of your proposal… so please correct me if I'm wrong). Blaise, you said "Here we are sending a message that may or may not be received by an SDO client.". If a non-SDO client (e.g. a client not able to understand the sdo:oppositeProperty) receive this XML document, I am wondering how this client will be able to get a sense that A1 is the actual container of B1 (if A1 is contained by B1 element in the XML document). In the current version of technical root, I would agree that it seems hard to use B1 as the "root" of the datagraph. But technical root only fails here because we're trying to serialize an object that has a container. If a B instance is created without any container, it can (hopefully ) be serialized to XML. Now, more generally speaking, if containment is used as aggregation, does it make sense to use a contained object as root object of the datagraph? Again, from an Xcalia point of view, a contained object might have no existence without its container and the XML structure directly reflects the Container/Contained relationship. Thanks, François. De : Blaise Doughan [mailto:blaise.doughan@oracle.com] Envoyé : mercredi 23 avril 2008 18:10 À : sdo@lists.oasis-open.org Objet : Spam detected by the Fortinet Antispam Re: AW: [sdo] Containment discussion Hello All, XML serialization refers to two concepts in SDO: 1. The XML representation used when a data object goes through Java serialization (see SDO 2.1 section 6 "Java Serialization of DataObjects"). Here we are sending data objects from one SDO environment to another SDO environment. In this arena we can focus on making the transfer of data as efficient and portable as possible (which may require Xcalia's technical root). 2. The XML representation used when a data object is marshalled by XMLHelper. Here we are sending a message that may or may not be received by an SDO client. This is the compelling use case, as it relates to how SDO interacts with other technologies (Web Services, Java EE, .Net, etc.). In this case if we marshal/save an employee data object it would be unexpected to have the result wrapped in a technical root. Here is where the Oracle proposal (SDO-124) fits. Oracle Proposal (SDO-124) and SDO 2.1 SDO 2.1 allows the current metadata: Department --containment --> Address Department --containment --> Employee Employee --non-containment --> Address With this SDO 2.1 compliant metadata it is possible to create a graph that can not be serialized. All you need to do is to specify an instance of Address on an instance of Employee that is not containment by an instance of Department. The algorithm in the SDO 2.1 spec requires that you specify enough containment relationships (and obey them). The Oracle algorithm (SDO-124) makes the assumption that if you specify containment relationships you are specifying enough (just like SDO 2.1), in addition if no containment relationships are specified then there is special treatment for them. Comparing the Containment Proposals Oracle Proposal (SDO-124) One of the interesting aspects of the Oracle proposal (SDO-124) is that XML messages can be sent relative to a particular SDO type. This is very useful for DAS implementations that want to have per type find operations and then send this as an XML message. If the underlying metamodel had a containment relationship between Department and Address then the Oracle proposal (SDO-124) could produce an XML message wrt Department and another XML message wrt Employee. Xcalia Proposal The above use case is not addressed by the Xcalia proposal. SAP's proposal (SDO-66) The SAP proposal (SDO-66) does address this use case, my understanding of that proposal is that a set of metadata would need to be defined per root type and stored in its own instance of HelperContext. DAS would realize data in a HelperContext, and then project that data into another HelperContext that corresponds to the root type of the query. The onus would be on the user to ensure that the types between the HelperContexts are compatible. -Blaise Barack, Ron wrote: Hi, I'd like to revive this mail thread. I think the first question has been answered in Xcalia's document. To me, the compelling use-case is that we have two SDO based applications that want to communicated. Neither cares about specifying an XSD to which the message should conform, they just want to send SDOs over an XML wire. That leaves the second question... now, the question is specifically to Oracle. Technical Root can transform *any* graph to XML. I think there is no tuning that can be done to the Oracle proposal to achive this, because Oracle's proposal tries to do something that is impossible: it tries to add properties to the basic structure to achieve closure *based on examining the metadata*. TechRoot does something else... it works directly with the data in the graph, not with the metadata. That being the case, what are the reasons for preferring Oracle's algorithm over TechRoot? Ron ________________________________________ Von: Barack, Ron [mailto:ron.barack@sap.com] Gesendet: Mittwoch, 9. April 2008 00:33 An: sdo@lists.oasis-open.org Betreff: [sdo] Containment discussion Hi Blaise and Xcalia Two questions... 1. Before we embark on a long discussion of this (or any other) proposal for dealing with containment, I think it's first important to get our use-cases straight. Which use cases are you aiming at here, and why is the functionality provided by issue 66, and in particular the convenience methods based on it, not the best means to deal with it. As I understand your use-case, it seems to fit very well indeed to issue-66. 2. This propoal does not generate a closed XML document from an arbitrary SDO data graph. There are other algorithms that do, for instance, Xcalia's TechnicalRoot proposal. I would think that the main requirement of such an approach to containing is that it can produce XML out of any data graph. What is the advantage of prefering this approach to Technical Root? Best Regards, Ron --------------------------------------------------------------------- To unsubscribe from this mail list, you must leave the OASIS TC that generates this mail. You may a link to this group and all your TCs in OASIS at: https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php
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