Rational & Eclipse UML2 Tools – Flawed UML Component Connections

Connecting UML Components with the Ball and Socket notation in Rational Software Modeler (RSM/RSA) and Eclipse UML2 Tools is not fully implemented or flawed. Too fully understand my point you have to keep in mind that these tools are for modeling, not just drawing a picture/diagram. Thus the internal model representation of what you diagram must be correct and complete.

The Need:
I discovered this issue while trying to design a suitable domain specific language/model for architects to talk about systems and what interfaces/data connections they had between them. The users understand components, so our systems were components. Additionally, interfaces at a high level make sense for being an “agreed upon” contract of interaction between systems. So, the components will realize the interfaces or <> them to show providing and consumption between the systems. The figure below shows two examples of this.

If you look closely at the diagram you will note that the ball and socket do not really connect, which is the first indication that there is a problem. RSM will not let you connect the ball and socket visually or in the model. The Eclipse UML2 Tools will let you connect them, but it fails to model them correctly, though it is still in the early phases of open source development so it kind of gets a pass for most of this discussion.
UML Defines:
So what does UML say should be possible, both from a visual representation (syntax) and model structure (more semantics)? The UML specification 2.2 (Superstructure) says on pg 151 in section 8.1 at a high level that:
“As a result, components and subsystems can be flexibly reused and replaced by
connecting (“wiring”) them together via their provided and required interfaces….
In addition, the BasicComponents package defines specialized connectors for ‘wiring’ components together based on interface compatibility.”
The Assembly kind of Connector
At the syntax and semantics level however there are a few details to understand. The major construct to support “wiring” are Connectors. The ComponentBase extends the Connector definition allowing for two kinds of Component specific Connectors, Delegation and Assembly. Also, you “wire” both components and component parts/ports which can make the spec hard to read. It states on page 155 in section 8.3.3:
“The connector concept is extended in the Com ponents package to include interface based constraints and notation.
A delegation connector is a connector that links the external contract of a component (as specified by its ports) to the internal realization of that behavior by the component’s parts. It represents the forwarding of signals (operation requests and events): a signal that arrives at a port that has a delegation connector to a part or to another port will be passed on to that target for handling.
An assembly connector is a connector between two components that defines that one component provides the services that another component requires. An assembly connector is a connector that is defined from a required interface or port to a provided interface or port.”
Notice that for assembly it does not say compo nent part, but components and uses the word between. To make things confusing the major examples (pg 153 Figure 8.15) are on Component Instances that are Parts, not between components so to be sure I also found the following on page 156 under constraints:
“[5] An assembly connector must only be defined from a required Interface or Ports to a provided Interface or Port.”
An interesting note, but I will go no deeper is that the table 8.2 makes it sound like connecting the ball and socket by a usage/dependency would be equivalent, especially when you factor in
Figure 8.14. Table 8.2 from page 160:
So, the assembly connector defined in UML supports connecting the ball and socket between components, which should be reflected in the model as an Assembly kind of Connector.

Ecore/EMF Provides:
It turns out that the Ecore/EMF model of UML which Rational and Eclipse UML2 Tools leverage support the Assembly Connector per the UML spec. The below two figures show from Eclipse the construction of a component required interface connecting via an Assembly Connector to the same interface provided/realized by a component. The properties could be set and the selector filtered the options correctly given that the interface type had to match.


How Rational (RSM) FAILs gracefully:
In Rational you cannot even create an assembly connector between two components either visually or in the model. The diagram canvas will not allow you to select a component that is not an instance nor will it let you specify it when you are drawing a new (yet to be typed) line. In the model if you try to add a new relationship between two components it will not give you the assembly connector option.
Even worse if you try to connect the ball and socket in Rational with a use or depends you will actually be connecting the interface to itself, see below. Basically the ball and the socket are representations of the interface, not the provided or required ones.

Sadly, Rational provides the Assembly connector and even renders it fine when you are using instances of components (Parts) in the structural view inside a component. So, in my estimation the just mis-understood the specification or they did not keep up with the changes to UML as this was added as part of 2.0 from what I can tell.
A bug will be logged with IBM for the Rational Software Modeler (RSA/RSM) tools, and the ID/Link to it is TDB.
January 1, 2010 | No Comments »

Buried in the depths of Eclipse Team (Sync), it can support UML Models after all.

The short lesson: When looking at eclipse features dig deep and work off the website and examples. Books are outdated quickly and are often written to just the major usage of a package or feature. Never be to proud to use the eclipse project specific mailing list.

The story: Whenever I take time off work, I invariably take on creating some new thing or read a technical book, basically just go down a rabbit hole of some kind as much of my day to day work requires abstraction from the details and hands on coding.

The Christmas 2009 break is no different. This time I dug a little deeper than I normally do with eclipse and plug-ins. I have been creating an eclipse plug-in to import UML objects from an outside server which houses use cases, requirements, and test cases. I figure why copy and paste or manually sync them which you can have a wizard done. Great so after a COM Bridge, EMF Transactions, UML Profile, and a shovel I have an import working. I did not do this in a vacuum, but instead have been going off, eclipse books, the eclipse.org dev websites etc. I had checked into Eclipse Team about 8 months back and found it was decidedly IResource (File/Folder/Project/WorkspaceRoot) limited as all of the methods seem to require IResource to operate. This lead me to just drop the “Syncronization” and Team approach to integrating UML models with outside data sources. Heck I figure even IBMs Rational suite has to do all the sub-file (UML object) comparisons with a comparitor, that must be it.

As I completed a workable Alpha of the importing plug-in and began to lust after the export, update, and delta features one expects when collaborating, I decided to double check that the Eclipse Team (CVS,SVN, etc) really would not work. Into the rabbit hole I went. This time as I went to the website and played with examples. They all showed promise as features had been added in recent releases. The org.eclipse.team.examples code is helpful for understanding this seriously complex package/feature. But more importantly there had been additions since 3.2 and how there seemed to be support for Logical Models. Great models are what I am doing.

So I really dig in. The trouble was that I cannot find a good example to how this would be done in a non trivial way. The example Logical Model code was trivial as each “Model Element” was still a IResource, so it did not show that this could be done. Even though they had in the API/Eclipse documentation mentioned Ecore models it all seemed to be still focused on IResources. Finally, however, I am convinced that the Logical Model Team feature set will meet the need of Syncing non-IResource model components, ie sub-file detail level representation. The wiki page about the team logical model objective said it most clearly.

The following paragraph, taken from the Eclipse 3.2 plan, describes the motivation for the logical model integration support that was added in Eclipse 3.2.

The Eclipse Platform supports a strong physical view of projects, files, and folders in the workspace. However, there are many situations where a physical view is not the most salient or useful for many purposes. In some cases, multiple distinct objects happen to be stored in a single file, like an archive. Conversely, in other cases, something that is logically a single object is stored across multiple files. This discrepancy between logical and physical creates problems for common operations such as searching, comparing, and versioning, which need to work in the physical realm. Eclipse should support some way of mapping between a logical view and the physical organization of files on disk.
At the beginning of the 3.2 development cycle, we captured the requirements from several clients in a requirements document.

And while I was writing this post I found THE emf example that has not been merged in with the other org.eclipse.team.examples, seriously, I can’t even find an email dev list to post about this issue. Also, the link on that page is dead, I found the code in the CVS archive however.

So, hours of playing with the examples, running them in the debugger trying to figure out the slight of hand and object types being used, and reading pages of seemingly contradictory documentation, nearly giving up assuming that it must not work, only to search or dig just a little bit more and find out it is supported. I know way more about the Team feature set now then I actually need to know for writing the plug-in. Hopefully next time I will navigate the eclipse web a little more efficiently, or I am find a mailing list and enlist the help of others rather than just digging deeper into my rabbit hole alone, and even Google Search failed me.

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