23rd December, 2008 - Posted by rafael.chaves - 5 Comments
No tool is an island. That is even more important when we are talking about highly focused single-purpose tools such as the TextUML Toolkit. As you probably know, the TextUML Toolkit is a tool for UML modeling using a textual notation, but that is about it. The TextUML Toolkit itself won’t help if you need features such as code generation, reverse engineering or graphical modeling/visualization. That might look as a negative thing to some, but that is by design. I am a strong believer of separation of concerns, component-based software and using the best tool for the job, and that is reflected in the design of the Toolkit.
This post will describe how to use models created by other UML2-compatible modeling tools from models you create using the TextUML Toolkit. I plan to cover other areas of integration in future posts.
Reading models created by other UML tools using the TextUML notation
If you have the TextUML Toolkit installed, one of the editors available for UML files is the TextUML Viewer. As the name implies, it is not really an editor, i.e., you cannot edit models with it, just visualize them using the TextUML notation. But it is an useful tool for reading UML models you don’t have the source for, i.e. models created by other UML2 modeling tools.
Using models created by other tools…
There are a few different ways of using models created by other UML modeling tools from your models created in TextUML.
…by co-location
In this method, you just drop the UML model you want to use to at the root of your TextUML (i.e. MDD) project. All models at the root of the same MDD project are considered to be in the same repository and thus you can make cross-model references by either using qualified names or importing the package and using simple names.
This method is dirty simple, but it forces you to keep the foreign model at a specific location, potentially forcing you to keep multiple copies of the model.
…with project references
In this method (available starting in version 1.2), the UML model you want to use is in a different project than the one you want to refer it from. You just open the properties dialog for your TextUML (MDD) project and add the project providing the UML model you want to use to the list of referenced projects. Now models at the root of that project will also be visible from your TextUML (MDD) project, in other words, they are also seen as part of the same repository.
This method is more powerful than the previous one, as now models can be shared by reference instead of by copying. There is a limitation still: the models you use ought to be part of some project in the workspace, so you cannot refer to models stored at arbitrary locations in the file system or models that are contributed by Eclipse bundles.
…by explicitly loading them
For this method, you use the load directive to load an external model located by a URI.
This method allows you to load any model, provided its location can be represented as a resolvable URI. That is the case of any file system path, or Eclipse platform URLs. The caveat is that some URIs such as file system URIs are not portable, so they are are bound to be invalid on other machines.
The entire truth…
…is that even if you are using only the TextUML Toolkit for building UML models, these are the same mechanisms for creating models that make cross-package references (see also the TextUML Guide). For the TextUML Toolkit, all UML2-compatible models are equal, no matter how they were created.
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2nd December, 2008 - Posted by rafael.chaves - No Comments
Yesterday I checked in support for UML primitive types in the TextUML Toolkit. As an example of the syntax, here is the UMLPrimitiveTypes model, shipped in Eclipse UML2, rendered by the TextUML Source viewer:
[Standard::ModelLibrary]
model UMLPrimitiveTypes;
apply Standard;
primitive Boolean;
primitive Integer;
primitive String;
primitive UnlimitedNatural;
end.
As you can see, primitive types are declared using the keyword ‘primitive’, and cannot specialize other types or have structural features (thus there is no ‘end’ terminating the type declaration). To be honest, I am not sure this is the intended semantics, as the UML specification does not seem to explicitly disallow that.
Here is the breakdown of the change sets (r188-191):
- automated tests (r190)
- parser and model generation (r191)
- textual renderer (r189)
- editor (r188)
To be frank, the only test case added was quite trivial:
public void testPrimitiveType() throws CoreException {
String source = "";
source += "model someModel;\n";
source += "primitive Primitive1;\n";
source += "end.";
parseAndCheck(source);
PrimitiveType found = (PrimitiveType) getRepository().findNamedElement(
"someModel::Primitive1", IRepository.PACKAGE.getPrimitiveType(), null
);
assertNotNull(found);
}
But it is a good start. It ensures parsing works, and the model generated has the intended element created under the right parent package.
Any suggestions of what UML feature to cover next? And what is your take? Can UML primitive types have structural features or specialize other types/implement interfaces?
(By the way, if you want to understand how the TextUML Toolkit is implemented, feature posts like this are a good starting point)
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28th November, 2008 - Posted by rafael.chaves - 2 Comments
Just checked in a new feature in the TextUML Toolkit: support for data types (a.k.a. structs). This is an example of a data type declaration:
datatype UserName
attribute firstName : String;
attribute lastName : String;
end;
You can declare operations and specialize other classifiers as usual.
Change set
Here are the individual changes per plug-in (r177-r186):
There, nice and easy. Well, actually, I ended up doing a second commit because I forgot to ensure a data type specializes only other data types. But now that has been taken care of.
As usual, suggestions of UML features to support in the TextUML Toolkit are most welcome.
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11th November, 2008 - Posted by rafael.chaves - 1 Comment
Just checked in a new feature in the TextUML Toolkit: required extensions for stereotypes (honestly, I didn’t know about that feature in UML until I read this post on the Eclipse UML2 newsgroup).
The following is a stereotype extending two metaclasses (uml::Class and uml::Operation):
profile my_profile;
import uml;
stereotype foo extends Class, Operation required
end;
end.
In the example above, the extension of Operation is required, the extension of Class is not.
Change set
The change set to implement required extensions in the TextUML Toolkit (issue #2266268) was quite small (btw, kudos to the UML2 project for providing the best API for UML out there).
Here are the individual changes per plug-in (r153-r156):
Any other UML feature you would like to see exposed in the TextUML notation? Suggestions are welcome.
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7th November, 2008 - Posted by rafael.chaves - 1 Comment
The first milestone build of the next TextUML Toolkit release is now available from the milestone update site. This preview build is the first to include support for modeling behavior using action semantics. I hinted at this capability here before, and I plan to cover action semantics in the TextUML notation in following posts. But most people will get the gist of the notation from the examples below:
Here is an example of a UML model of an Account class represented in TextUML:
model bank;
import base;
class Account
attribute accountNumber : String;
attribute balance : Integer;
operation withdraw(amount : Integer);
begin
self.balance := self.balance - amount;
end;
operation deposit(amount : Integer);
begin
self.balance := self.balance + amount;
end;
static operation newAccount(number : String,owner : Client): Account;
begin
var newAccount : Account;
newAccount := new Account;
newAccount.accountNumber := number;
newAccount.balance := 0;
link ClientAccount(owner := owner, accounts := newAccount);
return newAccount;
end;
end;
class Client specializes Object
attribute name : String;
static operation newClient(name : String): Client;
begin
var newClient : Client;
newClient := new Client;
newClient.name := name;
return newClient;
end;
end;
association ClientAccount
navigable role owner : Client[1];
navigable role accounts : Account[0, *];
end;
end.
And here an example of a test driver ‘program’ (note the use of a closure for looping through a collection of objects):
package test;
apply base_profile;
import bank;
import base;
class TestDriver
[entryPoint]
static operation run();
begin
var john : Client, mary : Client,
account1 : Account, account2 : Account, account3 : Account;
john := Client#newClient("John Doe");
mary := Client#newClient("Mary Doe");
Console#writeln("Created: ".concat(john.name));
account1 := Account#newAccount("1234-1", john);
account2 := Account#newAccount("1238-2", mary);
account3 := Account#newAccount("2231-7", john);
Console#writeln("account owner: ".concat(account1->ClientAccount->owner.name));
Console#writeln("account number: ".concat(account1.accountNumber));
Console#writeln("initial balance is: ".concat(account1.balance.toString()));
account1.deposit(2000);
Console#writeln("after deposit, balance is: ".concat(account1.balance.toString()));
account1.withdraw(500);
Console#writeln("after withdrawal, balance is: ".concat(account1.balance.toString()));
/* Now show information for all accounts. */
Account extent.forEach(
(a : Account) {
Console#writeln("*******");
Console#writeln("Owner: ".concat(a->ClientAccount->owner.name));
Console#writeln("Number: ".concat(a.accountNumber));
Console#writeln("Balance: ".concat(a.balance.toString()));
}
);
end;
end;
end.
And here is the output of the test driver program, produced by running it on the Libra UML runtime (not part of the TextUML Toolkit):
Created: John Doe
account owner: John Doe
account number: 1234-1
initial balance is: 0
after deposit, balance is: 2000
after withdrawal, balance is: 1500
*******
Owner: Mary Doe
Number: 1238-2
Balance: 0
*******
Owner: John Doe
Number: 1234-1
Balance: 1500
*******
Owner: John Doe
Number: 2231-7
Balance: 0
Alternatively, one could have generated 100% of the code for a target platform of choice, given that all the information necessary for that is in the model. Note that code generation is not part of the TextUML Toolkit.
Do you want to give it a try? Install M1 from the milestone update site. You can also fetch the example projects from here.
It is certainly a rough stone. I am counting on the community feedback to figure out what areas need to be smoothed first. Please provide your feedback or ask questions on the TextUML Toolkit forums.
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2nd November, 2008 - Posted by rafael.chaves - 6 Comments
Do you know what UML can do for you? I mean, did you know that UML models can actually do things?
One of the least known features of UML is that you can model detailed imperative behavior. The UML “instruction set” can do things like:
- create and destroy objects
- create and destroy links (associations) between objects
- read and write attributes and local variables
- invoke operations and functions
- throw and catch exceptions
- conditional statements
- loops
That is quite amazing, isn’t? And all that while still preserving a high level of abstraction. Such capability is generally referred to as ‘action semantics’. Action semantics provides the basic framework for executability in UML and has been there for quite a while now. It was originally added to the spec, first as patch, in UML 1.5 (2003), and then more seamlessly integrated into UML 2.0 and following spec releases.
Action Semantics and TextUML
An even more well-kept secret is that the TextUML notation supports UML action semantics and thus the creation of fully executable UML models. This support is not yet shipped as part of the TextUML Toolkit, but will be in the next release. Meanwhile, if you want to give it a try or take a closer look, you will have to grab the source from the SVN repository.
I plan to go into more details in the near future, but just to wet your appetite, here is one example of an executable UML model described in the TextUML notation:
package hello;
apply base_profile;
import base;
class HelloWorld
[entryPoint]
static operation hello();
begin
Console#writeln("Hello, World");
end;
end;
end.
Cool, isn’t? If you had a UML runtime, this model could be executed even before you made a decision about what platform to target. Also, if your code generator were action semantics aware, you could trigger code generation for the target platform(s) of choice, with the key difference that you could achieve (or get very close) to full code generation, as the model now also describes behavior. No more of that monkey business of having to edit the generated code and manually fill in all those /* IMPLEMENT ME! */ methods.
Do you think this has value? Would you want to work with a tool that supported that? I am really keen on knowing your opinion.
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15th October, 2008 - Posted by rafael.chaves - 4 Comments
This is actually old news for many people, but recently I learned (by pure chance) that the OMG issued a RFP for a “Concrete Syntax for a UML Action Language”. Letters of intent are due on December 8th. Submissions, one year after. OMG members only need apply (Aww…). I wonder if anyone in the Eclipse Modeling project is involved in submitting a proposal. Anyone?
Soapbox: since version 1.5, UML has had support for algorithmic behavior specification, commonly called action semantics. It is still hardly used, and most people that consider they know a lot of UML have never noticed it. Some people believe that the lack of an official concrete syntax for action semantics is a barrier to adoption. You see, the OMG defined the semantics and an abstract syntax, but left concrete syntax as an exercise for tool vendors.
As I wrote here before, I don’t really see the value in the OMG godfathering one concrete syntax over all others. Of course, we are talking here about a syntax for human beings, not for tools. Tools certainly don’t need a human-readable concrete syntax, a standard binary or XML format will do. The problem is: we all have our own preferences for what makes a good syntax, and there is no single syntax that will make everybody happy, so we are bound to have multiple concrete syntaxes anyway. We all like interoperability between tools, but when it comes to sugar, we like choice.
But maybe I am wrong. Maybe an OMG-blessed C-like concrete syntax for UML is all that is missing for Executable UML to become mainstream in the software development community. Go figure, we are an amusing bunch. Personally, I don’t care that much. I have been a Java developer for around 12 years now, so I can certainly stand another C-like syntax. We are not talking about a language anyway, it is just a syntax for an existing language, and syntax, a bit like UI, is inherently disposable, if you take it away, the real stuff is still there.
One clear positive outcome of the RFP is that submitters must provide, along with the proposal for a concrete syntax, any changes to fUML* that would be required to support such action language. That will probably help closing some gaps in the UML specification that make it hard to execute if you are stuck with the standard.
There are many other interesting bits in the proposal, but I will leave a more detailed analysis to a future post.
* the Executable UML Foundation Submission says:“Foundational UML Subset (fUML) is that subset of UML required to write ‘programs’ in UML”
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14th October, 2008 - Posted by rafael.chaves - No Comments
I posted this earlier this week on the UML2 newsgroup, thought I would share it here too…
I published a TextUML rendition of the UML 2.1 metamodel that is shipped by Eclipse UML2 here (warning: 5.9k lines, 370Kb of text). It starts like this:
(...)
model uml;
apply Ecore;
apply Standard;
import ecore;
(* A comment is a textual annotation that can be attached to a set of elements. *)
[Standard::Metaclass]
class Comment specializes Element
(* Specifies a string that is the comment. *)
[Ecore::EAttribute(isID=false,isTransient=false,isVolatile=false,isUnsettable=true,annotations=[])]
public attribute body : String;
(* References the Element(s) being commented. *)
public attribute annotatedElement : Element[0, *];
end;
(...)
Thought it could be useful to anyone wanting to have a quick look at the UML metamodel. The TextUML renderer does not support all UML element types, so some elements might be missing/incomplete.
I think that is a nice demo of the textual browsing capabilities in the TextUML Toolkit. Of course, much more could be done in that area. If you feel like lending a hand, any help (bug reports included) will be much appreciated.
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16th September, 2008 - Posted by rafael.chaves - No Comments
Shorthand notation for both composite and aggregate associations has just been checked in (r99-r100). It follows the same spirit as the existing shorthand for plain associations (a.k.a. references).
composition <end-name> : <referenced-type-name>;
or
aggregation <end-name> : <referenced-type-name>;
That will result in a new unnamed association with two member ends, one named, owned by the declaring classifier, with composite or shared aggregation type, and another unnamed, owned by the association itself.
Change set explained
When adding a new feature to the notation, the typical change set contains:
- updates to the affected grammar production rules
- implementation of the corresponding model generation handling code
- a few test cases.
In the case of the features presented in this post, the grammar change was quite simple (nicer view):
--- trunk/plugins/com.abstratt.mdd.frontend.textuml.core/textuml.scc 2008/09/16 05:47:13 99
+++ trunk/plugins/com.abstratt.mdd.frontend.textuml.core/textuml.scc 2008/09/16 05:47:20 100
@@ -341,7 +341,9 @@
attribute_decl = attribute identifier colon type_identifier optional_subsetting semicolon ;
- reference_decl = reference identifier colon type_identifier optional_subsetting semicolon ;
+ reference_decl = reference_type identifier colon type_identifier optional_subsetting semicolon ;
+
+ reference_type = {association} reference | {composition} composition | {aggregation} aggregation ;
optional_subsetting = subsets qualified_identifier | {empty} ;
In other words, where one could declare a reference, one can now declare also a composition or an aggregation (gotta love the readability of SableCC grammars…).
The corresponding model generator (a.k.a. compiler) changes were quite trivial as well, even more so if you consider I inadvertently checked in a fix to an unrelated bug around comments (just ignore the changes in lines not in the 300′s).
In terms of lines of code, the bulk of the changes were in the test class for associations, where I added three test cases. I had postponed writing tests for the reference shorthand notation, so I took this opportunity to write a test for it too.
As most test cases in the TextUML Toolkit test suite, the new test cases in AssociationTests have the following layout:
- one or more compilation units with TextUML source code are declared
- source code is compiled and the resulting errors verified (most test cases won’t expect errors)
- the resulting model is checked – were the expected elements created? Do they have the expected features?
Talking about tests
The TextUML Toolkit has a modestly sized test suite (~130 test cases) at this time. It could use dozens, probably hundreds more, but most features are covered to so some extent.
However, as important as coverage, is how much one can learn about the piece of software being tested by reading its test suite. And here is where I believe the TextUML Toolkit’s test suite shines. For example, by reading the test classes, one could (maybe more effectively than by reading the notation guide), learn how the following UML features are exposed by the TextUML notation:
Trivia: can you find out from the test suite the difference between a private and a public package import? Give it a try and let me know if I am lying… by the way, the notation guide does not cover that yet, although the UML specification, of course, does.
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10th September, 2008 - Posted by rafael.chaves - 5 Comments
I often see the TextUML Toolkit being compared to tools that produce UML diagrams from textual descriptions. Examples of tools like that are ModSL, MetaUML and UMLGraph. But that doesn’t really make sense, and here is why: these tools produce diagrams from text. The TextUML Toolkit produces models from text. But what is the difference between models and diagrams?
According to Wikipedia:
- A diagram is a 2D geometric symbolic representation of information according to some visualization technique.
- A model is a pattern, plan, representation (especially in miniature), or description designed to show the main object or workings of an object, system, or concept.
Note that even though both terms are defined around the word “representation”, the term “diagram” implies graphical visualization, whereas the term “model” admits any kind of media, basically because models have no concrete form per se.
Now, please, if you are not convinced yet, read aloud 5 times: MODELS ARE NOT DIAGRAMS!
If that didn’t work, well, maybe the facts below will help:
- models, not diagrams, are the subject matter of model-driven development.
- models, not diagrams, can be validated.
- models, not diagrams, can serve as input to code generation.
- models, not diagrams, can be automatically generated from reverse engineering source code.
- models, not diagrams, can be executed.
Even though diagrams are commonly used for representing models, they are not the only way, and non rare not the most appropriate one (yes, I am talking again about the virtues of textual notations, but I won’t repeat myself).
P.S. Maybe it helps adding to the confusion the fact that the TextUML Toolkit has an optional feature that will generate class diagrams automatically from the UML models created with it. However, that is just an optional, loosely integrated feature, and it is definitely not the Toolkit’s thing. Weirdly enough, from my observation, that feature is the main reason most people become interested in the TextUML Toolkit. Well, go figure.
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21st August, 2008 - Posted by rafael.chaves - No Comments
I just completed the code for supporting parameter direction modifiers. When this feature makes into the next build, modelers will be able to choose for named parameters any of the standard parameter direction kinds: out, inout, or (the default) in. By the way, the syntax for specifying return types remains the same. Here is an example:
operation op1(in p1 : String, out p2 : String);
Java developers might consider this feature unnecessary as there is only one way of passing parameters in Java, but for distributed applications (such as those using CORBA or web services) these modifiers are quite relevant.
The corresponding support for rendering operation parameter direction kind modifiers has been added to the TextUML model viewer (decompiler) and EclipseGraphviz graphical rendering component.
This is the first new feature since version 1.0 was released. The impact of implementing it was quite minimal to the code base, so I am looking forward to implementing the next notation feature. The question is: what feature? Any suggestions?
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6th August, 2008 - Posted by rafael.chaves - 6 Comments
One potential downside people often point out about using TextUML as a notation for UML is that it is yet another language to learn. But that is not really a well founded argument. TextUML is not a full-blown language, it is just an alternative notation for UML, the de facto standard language for modeling. The language semantics of UML are defined in terms of an abstract syntax, and even though the specification includes sections about the graphical notation, it clearly supports the idea of alternate concrete syntaxes.
Moreover, we really shouldn’t care much about the actual notation being used, be it the standard graphical notation, TextUML or any other textual notation. I surely don’t. Regardless what notation you use for creating UML models, in the end there is only one language. All you know about the semantics of UML model elements is still true no matter what syntax you choose (for instance, if you know your UML, you should easily become productive with the TextUML Toolkit by just glancing over the notation guide now and then). In fact, I predict a time where people will want to move between different notations across tasks and time. Also, in the same team, different people will be collaboratively creating UML models using different notations.
This will only be possible because supporting a new concrete syntax is much simpler than supporting a whole new language (by the way, that is the same reason why I believe UML-based DSLs to be a better option than homegrown proprietary DSLs, but I digress). Any reasonably good programmer armed with a parser generator and knowledge of the metamodel should be able to write a compiler for a textual notation for UML, and Eclipse makes it really easy to provide basic IDE features such as those you see in the TextUML Toolkit. Also, there are tools in the horizon such as IMP and TMF that will make these tasks really a breeze.
Meanwhile, you can stick with what is here today. 
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11th June, 2008 - Posted by rafael.chaves - No Comments
Contrary to my original intention of working this week on code generation and the sample application, I have been doing some improvements in the graphical visualization of UML models in EclipseGraphviz. EclipseGraphviz (a spin-off of the TextUML Toolkit) is an open source component (EPL) that integrates Graphviz into Eclipse, and among other things, can generate UML class diagrams from Eclipse UML2 models on the fly.
After fixing a couple of bugs, I decided to add a preference page to give some level of control over the way the diagrams are laid out. Here is what it looks like:
You can now turn on or off several adornments such as association end names, multiplicities and membership. For example, this diagram was rendered using the options shown above:
Whereas the following one was rendered for the same model while having only the “Create constraints for association navigability” option checked:
As you can see, enabling constraints based on association navigability can significantly alter the diagram layout. One good reason for enabling that option is to avoid diagrams that grow too much horizontally (as Graphviz will put all nodes of the same rank on the same row), but I personally prefer the former layout.
Side note: I considered dropping the graphical visualization feature altogether for 1.0, as I see it as just a nice to have, and am not totally happy with the quality of the diagrams generated by Graphviz. But every bit of feedback I got for the TextUML Toolkit was that the graphical visualization was really nice, so I changed my mind. But unless serious bugs are found in this area, I have no plans of touching the EclipseGraphviz code again until after I complete the 30-day challenge.
Side note #2: I expanded the FAQ to cover the issue of notation choice and the role of EclipseGraphviz in the TextUML Toolkit.
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2nd June, 2008 - Posted by rafael.chaves - 11 Comments
There was a recent thread about UML on Slashdot, as a reaction to this blog post . The headline: “Is UML Really Dead, Or Only Cataleptic?“. Many posters are clearly bitter towards UML. There seems to be a strong preference for using UML as a communication tool as opposed to as a basis for partial or full code generation (see post on UML modes). Many also complain that the graphical notation is cumbersome and that it hurts productivity (+1!). A few actually like UML; however, it is said that the UML specification is vast and complex and that you should pick the parts of UML that make sense for your case/goals (+1 here too).
Lots of interesting points, but the most negative posts are just misinformed. But that is Slashdot, what should I expect? Java and Eclipse have, in general, a poor receptivity on Slashdot, so I guess UML is in good company.
Of course, while I disagree with those that ditch UML because it was not properly employed in some project they worked, I strongly agree with the complaints about UML (graphical) diagrams being cumbersome and hard to deal with, as I have written here before. But that is not a problem with UML per se, but with the fact most still see it as a graphical language.
UML certainly has its share of problems (design by committee, no reference implementation), but I strongly believe it is very useful and that there isn’t anything out there (I am talking to you, home grown DSLs) that can replace it as the lingua franca for model-driven development.
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5th May, 2008 - Posted by rafael.chaves - 4 Comments
TextUML is a textual notation for UML. The TextUML Toolkit is an Eclipse-based IDE-like tool for creating UML models using the TextUML notation.
Other tools follow the same approach. Emfatic (now an EMFT subproject) has been doing the same for EMF Ecore for a long time; the TMF project aims to be for textual modeling what GMF is for graphical modeling, and will be based on GMT‘s TCS and xText components.
Still, people are often puzzled when I explain what the TextUML Toolkit is. A common question is: “if I am going to write code (sic), why do I need UML anyway?“.
Dean Wampler from Object Mentor wrote on his blog a while ago a post entitled “Why we write code and don’t just draw diagrams“. It is a short post, but he presents very good points on why a graphical notation is usually not suficient and is bound to be less productive than a textual one when it comes to modeling details. For instance, on the saying “a picture is worth a thousand words“, Dean wrote:
“What that phrase really means is that we get the ‘gist’ or the ‘gestalt’ of a situation when we look at a picture, but nothing expresses the intricate details like text, the 1000 words. Since computers are literal-minded and don’t ‘do gist’, they require those details spelled out explicitly.”
Couldn’t have said it better.
I strongly advise you to read the original post in its entirety, but I will leave you with another pearl from Dean’s post (emphasis is mine):
“I came to this realization a few years ago when I worked for a Well Known Company developing UML-based tools for Java developers. The tool’s UI could have been more efficient, but there was no way to beat the speed of typing text.”
Enough said.
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7th February, 2008 - Posted by rafael.chaves - No Comments
One common misconception is that UML is a graphical language and that any tools adopting alternative notations (such as a textual one) are inherently non-compliant. That can’t be farther from the truth. Read on to understand.
The fact is that the UML specification clearly separates abstract syntax (the kinds of elements and how they relate) and semantics (what they mean) from concrete syntax (what they look like), and states that there are two types of compliance:
- abstract syntax compliance
- concrete syntax compliance
Concrete syntax compliance means that users can continue to use a notation they are familiar with across different tools. This is important when UML is used as a communication tool in a team environment. Architects, designers, programmers and even many business analysts speak the same language.
Abstract syntax compliance means that users can move models across different tools, even if they use different notations. This is essential when UML is used as a basis for model-driven development. You might want to use tool A for creating the model, tool B for validating the model, tool C for somehow transforming/enhancing the model and tool D for generating code from it (a common form of MDD tool chain).
The TextUML Toolkit uses a textual notation that strictly exposes the UML semantics, but it is not compliant with the language concrete syntax by any means. On the other hand, the toolkit uses Eclipse UML2′s XMI flavor for persisting models and thus is fully compliant regarding the abstract syntax. That is consistent with the vision for the product: a tool from developers for developers that want to build software in a more sane way: the model-driven way. Developers can create models using a notation they are more productive with. Models can then be used as input for code generation using many of the tools available in the market. If non-developers might frown upon a textual modeling notation, they will always have the option of using their favorite graphical-notation based tools for reading the models. I mean, if their tool of choice is abstract syntax compliant as well.
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18th December, 2007 - Posted by rafael.chaves - 4 Comments
Andreas Awenius, from Empowertec, was kind enough to devote not only one, but two blog postings on the TextUML Toolkit. While his first post was just a paragraph or two acknowledging the use of a textual notation for UML modeling in the TextUML Toolkit, his second post was a very detailed and balanced analysis on the whether using textual notations is a good idea. Even though the conclusion of his posting is that a graphical notation is superior to a textual one, I still agree with many points Andreas has made in his analysis:
- the presentation notation and the persistence format are completely unrelated concerns (exactly, see my previous comment on this).
- diagrams are views for models, focused on a specific aspect, and as such must show only what is needed and omit anything that is not essential. (perfect)
- there are “multiple ways to manipulate the repository, e.g. the conventional – graphical – way or a textual notation”. (yes!)
These are the very same facts that justify the existence of a tool such as the TextUML Toolkit.
- since user-oriented notation and persistence format are completely different things, you can please users with the most appropriate syntax for their needs (and that is text for many developers), without affecting interoperability with other tools, as tools interoperate at the level of the persistence format. The TextUML Toolkit achieves that by producing UML2 models as the native object file format.
- the graphical notation is great for creating views, but it is not that suitable for exposing all the details in a model. A textual notation has no problem doing that. The graphical notation is still useful, and this is why TextUML Toolkit will include a read-only graphical view for browsing the repository. And here is the first point I disagree with Andreas. He says: “a diagram must carefully be crafted manually, leaving out all irrelevant detail”. I say: automatically generated diagrams can still obey a set of preferences defined by the user (level of detail, color, font, etc). UMLGraph has been doing this for a long time (albeit by breaking some basic rules of separation of concerns, but I digress). The TextUML Toolkit will embed an upcoming version of UMLGraph in its next milestone.
- this is basically a conundrum of points #1 and #2. The model created will be the same (from the point of view of tools) regardless the user-facing notation. If users say they would rather use a textual notation, why forcing them to use a graphical one when there are no technical reasons to do so? Here is where Andreas makes several points to back his opinion based on technical and strategical reasons, most of which I (strongly to moderately) disagree. Instead of trying to refute each of those arguments (that is not how you encourage people to provide elaborate feedback), I will use them as an opportunity for driving awareness efforts around the Toolkit, the notation and our future offerings in upcoming posts to this blog.
The ‘raison d’être‘ for this blog is to establish connections with the modeling community at large, users and tool providers. I really appreciate the time and energy that Andreas committed to sharing his views on the TextUML Toolkit and the textual notation approach and am both grateful and honored for that. Thanks a lot, Andreas. Stay in touch. I hope at some point I can convince you that you are wrong!
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8th December, 2007 - Posted by rafael.chaves - 11 Comments
Last Thursday happened the 1st Eclipse DemoCamp in Vancouver. It was a very dynamic event, with nine short talks packed into little more than one and a half hours. Attendance was high, I was really amazed to see such a great turnaround. The audience saw a diverse range of interesting Eclipse-based projects being developed in Vancouver/Victoria.
I demoed the TextUML Toolkit and got good feedback and some very interesting questions. The idea of a using a textual notation for creating UML models is still not a very easy sell, and that continues to surprise me. Being a developer, I find working with a textual notation so much more natural than a graphical one that it makes it hard for me to see things from other people’s shoes. I plan to go over the issue of textual versus graphical notations on a future post.
All in all, it was a great event. Many thanks to Tasktop‘s Robert Elves and Mik Kersten for organizing it, to the Eclipse Foundation for sponsoring the event, and congrats to all presenters.
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1st December, 2007 - Posted by rafael.chaves - 5 Comments
In a recent thread on the EMF newsgroup, I came to realize that there are (at least) two EMFs, each belonging to a different class of product, and attending completely distinct requirements.
EMF’s native metamodel, Ecore, is a generic, lean object-oriented metamodel based on a subset of UML.
EMF’s runtime framework provides Java applications with runtime support for object models “including change notification, persistence support with default XMI serialization, and a very efficient reflective API for manipulating EMF objects generically” (source).
I am a happy user of EMF’s Ecore metamodel as a poor man’s UML (EMF team, please take that as a compliment). From Ecore-based models, using a compatible template engine, I can generate all code/artifacts that are prone to automation, be they Java code or not.
The runtime aspect of EMF is certainly useful to many applications, but certainly not to all or maybe even most. That is not to say that the EMF runtime does not provide a lot of value, as it clearly does given its popularity. Nor does it imply that the EMF runtime API has design flaws that prevent its use to be more widespread. The fact is that frameworks, while designed for extension, always impose a certain set of architectural decisions in order to provide value out-of-the-box. Those decisions are bound to make its use more suitable to some scenarios and applications than others. The goal is to make as many people happy as possible. It is clear that the EMF team has pulled off that trick. But that does not mean that using EMF-generated model code is appropriate for every Java application out there.
Model driven development maximizes reuse via a complete separation between problem domain and technological concerns. This separation is critical to allow us to build software in an obsolescence-proof way. EMF’s Ecore provides a good foundation for MDD in this sense, regardless the technology choices for the software being developed. The EMF runtime framework, albeit a valuable tool for a significant range of applications, brings with it a specific set of choices in terms of design and implementation decisions, and as such has a less universal applicability.
However, time and again I read comments in the EMF newsgroup that lead me to believe that this duality might have been accidental, and that the sole reason Ecore was created was to support the generation of Java applications based on the EMF runtime. If that is really the case, this is something that both amuses and worries me. My concern is that if the EMF team does not acknowledge the importance of Ecore as an independently useful product, technical decisions in the evolution of EMF might break the use of Ecore in contexts other than EMF-based Java applications.
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