Issue 3735: MOF rules should disallow certain composition relationships (uml2-superstructure-ftf) Source: (, ) Nature: Uncategorized Issue Severity: Summary: MOF rules should disallow composition relationships in instance metamodels where the container is in one MOF Package and the contained item is in another MOF Package and a dependency of the first package on the second is not allowed by the physical version of the metamodel due to MOF-imposed IDL generation rules. Reason for the issue: In the process of implementing an XMI-based interchange for UML 1.3, I have encountered a serious problem. This problem has to do with a divergence between the "Logical" and "Physical" model for UML 1.3 caused by rules imposed by MOF. In particular, in section 5.5 of the MOF 1.3 specification (27 Sep 99 version), "Preconditions for IDL Generation", requires that there be no cyclical dependencies between ModelElements in a meta-model. However, the UML 1.3 specification (June 1999) has a cyclical dependency between the Core and the Extension Mechanisms packages in the metamodel (See Figure 2-4). This cyclical dependency is explicitly disallowed by the precondition cited above. This circular dependency was removed from the "Physical Model" for UML 1.3 in order to allow CORBA IDL and XMI DTD declarations in conformance with the precondition. As a result of the removal of this dependency, there are tremendous difficulties expressing the composition relationship between the UML ModelElement and the UML Tagged Value (see figure 2-10). In fact, the TaggedValue XML elements cannot even be in the exported UML Package element -- they must be placed outside of it. This greatly complicates the export and import of UML 1.3 model files. Resolution: Revised Text: This is a UML 1.3-only issue and was resolved at UML 1.4. Actions taken: June 30, 2000: received issue March 9, 2005: closed issue Discussion: Better UML/MOF alignment is explicit goal of the UML 2.0 RFP. End of Annotations:===== From: "Mutschler, Gene O" To: issues@omg.org Cc: "Baisley, Donald E" , "Iyengar, Sridhar" Subject: Issue for UML RTF Date: Fri, 30 Jun 2000 19:23:52 -0500 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset="iso-8859-1" X-UIDL: 4`2e9[I7!!:[7e9C)3e9 Issue: MOF rules should disallow composition relationships in instance metamodels where the container is in one MOF Package and the contained item is in another MOF Package and a dependency of the first package on the second is not allowed by the physical version of the metamodel due to MOF-imposed IDL generation rules. Reason for the issue: In the process of implementing an XMI-based interchange for UML 1.3, I have encountered a serious problem. This problem has to do with a divergence between the "Logical" and "Physical" model for UML 1.3 caused by rules imposed by MOF. In particular, in section 5.5 of the MOF 1.3 specification (27 Sep 99 version), "Preconditions for IDL Generation", requires that there be no cyclical dependencies between ModelElements in a meta-model. However, the UML 1.3 specification (June 1999) has a cyclical dependency between the Core and the Extension Mechanisms packages in the metamodel (See Figure 2-4). This cyclical dependency is explicitly disallowed by the precondition cited above. This circular dependency was removed from the "Physical Model" for UML 1.3 in order to allow CORBA IDL and XMI DTD declarations in conformance with the precondition. As a result of the removal of this dependency, there are tremendous difficulties expressing the composition relationship between the UML ModelElement and the UML Tagged Value (see figure 2-10). In fact, the TaggedValue XML elements cannot even be in the exported UML Package element -- they must be placed outside of it. This greatly complicates the export and import of UML 1.3 model files. Additional material: In UML 1.3, the Extension Mechanisms package defines a composition relationship between ModelElement and TaggedValue, with the ModelElement as the owner (Figure 2-10). The ModelElement is in the Core package of UML, and the TaggedValue is in the Extension Mechanisms package. This is allowed by the existence of the a Dependency between the Core and the Extension Mechanisms package (Figure 2-4). There is also a Dependency between the Extension Mechanisms package and the Core package. Thus, a circular dependency relationship exists. This does not present a problem until it comes time to define the DTD necessary to export a UML 1.3-based model using XMI. Before such a DTD can be developed, XMI requires that a MOF-conformant realization of the published UML Metamodel be created. The published description of the metamodel is not MOF-conformant. (It makes use of AssociationClasses, for example, which are not MOF constructs.) The UML 1.3 RTF has created such a realization, calling it a "physical metamodel" (section 6.1). The key feature of this physical model is that, in accordance with the Precondition cited above, the Dependency of the Core package on the Extension Mechanisms package has been removed. The TaggedValue, although composed into the ModelElement, cannot be exported as part of the content model of the ModelElement, since MOF allows no Reference in the ModelElement that refers to the TaggedValue. The rules of XMI provide that, in this case, the Tagged Value be exported separately from the rest of the contents of the ModelElement. Indeed, it cannot even be exported as part of the Package containing the ModelElement. If the composition relationship between the ModelElement and Tagged value did not exist (by virtue of having been disallowed by a MOF rule forbidding compositions where the Package of the owner is not the same as or dependent on the owned Package), then other means could be used to assign ownership of TaggedValues, and they could presumably be exported as part of a Package, thus avoiding considerable difficulties in both export and import. Dr. Gene Mutschler Unisys Corp -- IMG 25725 Jeronimo Rd Mission Viejo, CA 92691 +1 949 380 6617 Sender: zmower Message-ID: <3A1461E8.C8FBB57B@btinternet.com> Date: Thu, 16 Nov 2000 22:38:33 +0000 From: Chris Moore X-Mailer: Mozilla 4.7 [en] (X11; U; Linux 2.2.14 i686) X-Accept-Language: en MIME-Version: 1.0 To: uml-rtf@omg.org Subject: [Issue 3735] MOF rules should disallow certain composition relationships Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii X-UIDL: c(Je9p@O!!O\Q!!MP\!! Hi, I'm trying to implement a UML repository based on the UML v1.3 IDL. I'd just like to reiterate Gene's point from a different perspective and extend it. There are no methods of ModelElement in the IDL for manipulating sets of TaggedValues or the reference to Stereotype on Fig 2.10 Extension Mechanisms. I can work around these by only using the references to ModelElement in TaggedValue and Stereotype but it sure is ugly. Unfortunately things get worse in the UML v1.4 beta R1 doc I've just read. The ModelElement to Stereotype association is now only navigable from the ModelElement end. If the IDL generation is the same as UML v1.3, I expect there to be no way to manipulate this association via the IDL. Yours Respectfully, Chris Moore http://sourceforge.net/projects/kuml/ http://www.freecase.seul.org/