I decided it was time to start using Eclipse 3.5 before it went RC or else if I find any blockers there won’t be time left for them to get fixed before the next release this Summer. I have been on the other side of the fence and know how frustrating it is when people only really start reporting bugs at the very end of the release cycle.

After I installed the 3.5 M6 SDK, I decided to install the TextUML Toolkit 1.2…

Nothing to install?

First surprise: no features would show on the update site! WTH? Well, turns out I had the Update UI to show available features grouped by category, but the TextUML Toolkit update site does not use categories. Unchecking the option to group by categories shows the four features in the TextUML Toolkit update site as it was usual in 3.4. Phew… I was just about to enter a bug report against the Eclipse update component (a.k.a. p2), when I found out that that unintuitive UI behavior has been recently addressed and the next milestone won’t show this problem any longer.

A roadblock

I managed to install the TextUML Toolkit, and that brought along EMF and UML2, which are required features. Since, at this time, the TextUML Toolkit does not specify version range for its dependencies, the latest versions of EMF and UML2 were automatically installed by Eclipse. That should be fine, I thought, as one of the Eclipse development key mandates has always been backward compatibility. But this time around that was not the case: the TextUML builder was failing to compile a TextUML source file that was making use of template parameters. Turns out the UML2 API around templates has changed in its version 3.0. Before (in UML2 2.2), a template parameter substitution could have multiple formal and actual parameters. Now it can have only one of each, and thus the TextUML Toolkit is (partially) broken in 3.5.

So much for core values, you might be thinking? Well, to be fair, this is a bit of a fringe case. The UML2 API is an Eclipse component, and as such should strive for backward compatibility too. However, it is also a high-fidelity rendition of the UML specification published by the OMG. In this case, the OMG fixed a bug (#9838) in the spec, and as often is the case with UML, that resulted in a change that was not backward compatible. If the OMG promotes changes that are not backward compatible, the UML2 team does not have much of a choice: in order to continue to closely implement the spec, it has to break the Eclipse guidelines.

And neither do I. For the TextUML Toolkit 1.2, I will have to issue a maintenance release (1.2.1) that will explicitly depend on UML2 2.2, thus avoiding the new version, and probably becoming incompatible with other UML modeling packages that only run on Galileo and UML2 3.0. For the next release of the TextUML Toolkit (1.3), I will have to adopt the new API and explicitly depend on UML 2 3.0.

That is how life goes… for some reason, I kind of feel like a flea crawling on the back of an elephant.

I strongly believe queries are an essential part of a domain model. As such, in our quest to have (UML) models that can fully (yet abstractly) describe object models for the common enterprise applications, we cannot leave out first class support for queries.

But how do you do queries in UML? The obvious answer seems to be OCL, but that is not the approach I am taking as OCL and UML have serious interoperability/duplication issues. Instead, I took the  middleweight extension approach.

First, we model a protocol for manipulating collections of objects (showing only a subset here):

class Collection specializes Basic
  operation includes(object : T) : Boolean;
  operation isEmpty() : Boolean;
  operation size() : Integer;
  operation exists(predicate : {(:T) : Boolean}) : Boolean;
  operation \any(predicate : {(:T) : Boolean}) : T;
  operation select(filter : {(:T) : Boolean}) : T[*];
  operation collect(mapping : {(:T) : any}) : any[*];
  operation forEach(predicate : {(:T)});
  operation union(another : T[*]) : T[*];
  (…)
end;

That protocol is available against any collection of objects, which in UML can be obtained by navigating an association, reading an attribute, invoking an operation, obtaining the extent of a class (remember Smalltalk’s allInstances), anything where the resulting value has multiplicity greater than one.

Note most of the operations in the Collection protocol take blocks/closures as arguments. Closures are used in this context to define the filtering criterion for a select, or the mapping function for a collect.

For instance, for obtaining all accounts that currently do not have sufficient funds, this method would do it:

static operation findNSFAccounts() : Account[*];
begin
    return Account extent.select(
        (a : Account) : Boolean {return a.balance < 0}
    );
end;

Note the starting collection is the extent of the Account class. That is very similar to what is done in the context of query languages for object-oriented databases, such as OQL or JDOQL. We then filter the class extent by selecting only those accounts that have a negative balance, by passing a block to the select operation.

When mapping that behavior to SQL, we could end up with a query like this:

select _account_.* from Account _account_ where _account_.balance < 0

Another example: we want to obtain all customers with a balance above a given amount, let’s say, to send them a letter to thank them for their business. The following method specifies that logic:

static operation findBestCustomers(minBalance : Real) : Customer[*];
begin
    return (Account extent.select(
          (a : Account) : Boolean { return a.balance >= minBalance }
    ).collect(
          (a : Account) : Customer { return a->AccountOwner->owner }
    ) as Customer);
end;

Note that we start off with the extent of Account class, filter it down to the accounts with good balance using select, and then map from that collection to a collection with the respective account owners by traversing an association using collect.

If that was going to be mapped to SQL, one possible mapping would be:

select _customer_.* from Account _account_
    inner join Customer _customer_
        on  _account_._accountID_ = _customer_._customerID_
    where _account_.balance >= ?

Much of this can be already modeled if you try it out with the TextUML Toolkit 1.2. But, you might ask, once you model that, what can you do with UML models containing queries like the ones shown here?

Since the models are complete (include structure and behavior), you can:

1. Execute them. Imagine writing automated tests against your models, or letting your customer play with them before you actually start working on the implementation.
2. Generate complete code. The generated code will include even your custom queries, not only those basic ones (findAll, findByPK) code generators can usually produce for you.

If you would like to see tools that support that vision, keep watching this blog.

So, what is your opinion?
Do you see value in being able to specify queries in your models? Is this the right direction? What would you do differently?

The TextUML Toolkit 1.2 is now available, 5 months after 1.1, when it first became an open source project. If you already got RC2 (1.2.0.200902011417), it is the same build, no need to upgrade again. Otherwise, just point the Eclipse update mechanism to:

http://abstratt.com/update/

Please see the feature page for a summary of the evolution of the TextUML Toolkit in terms of features across releases.

As usual, bug reports and feature requests are dearly appreciated. And if you need help, make sure to ask on the forum.

A new RC build of the TextUML Toolkit is now available. It has one bug fix since RC1. Basically, when rendering stereotypes, the metaclasses extended by the stereotype were not being shown. Not really critical, but isolated and safe enough to be fixed now. Pending any last minute bug reports by the community, it is likely this build will be promoted to 1.2 release early this week.

Also, while testing, I noticed that the Pet Store example was triggering a known Graphviz issue with associations navigable both ends, so I updated the petstore_models project so the relationship between Title and Payment was navigable only in one direction (Title -> Payment). I recaptured the class diagram images showing on that page using the Image Viewer “Save to File” function instead of screenshot sections.

Just trigger a software update for the TextUML Toolkit to get RC2.

Yikes, it happened again. A user reported that the TextUML Toolkit 1.2 RC0 build announced earlier this week wouldn’t run on Java 5 VMs (Mac users would be the most affected). This has just been fixed (one bundle was being compiled against Java 6) and a new release candidate is now available from the update site. If you too were seeing “java.lang.UnsupportedClassVersionErrors” running RC0, just go ahead and update to RC1.

The third milestone build and first release candidate of the TextUML Toolkit, the IDE for textual UML  modeling, is now available from the update site.

The feature page shows all the new features in this new release, but here they are:

• primitive types
• data types (a.k.a. structs)
• required extensions for prototypes
• behaviour modeling (a.k.a. action semantics)
• shorthand notation for aggregation and composition
• abstract stereotypes
• cross-project references

As you can tell, most of the work in the 1.2 release cycle was towards extending the TextUML notation with support for UML.

There were also several bug fixes, one of them being the first to be addressed by an external contributor (thanks, Massimiliano!).

If no serious issues are found with this milestone build, it will be promoted to 1.2 final by the next weekend. So, if you are using a 1.1.* build, make sure you upgrade it to a 1.2 release candidate build and start smoke testing with your usual workflows, and report any bugs you find.

UML is known to be a huge language, and that has two problems: it is too complex, having way more features than most applications will ever need, and can still be insufficient, as no single language will ever cover everybody’s needs.

In the article “Customizing UML: Which Technique is Right for You?”, James Bruck and Kenn Hussey (both from the UML2 team) do a great job at covering the several options for extending (or restricting) UML (James also made a related presentation at last year’s EclipseCon, together with Christian Damus, of Eclipse OCL fame). Cutting to the chase, these are the options they identify:

• using keywords (featherweight extensions)
• using profiles, stereotypes and properties/tagged values (lightweight extensions)
• extending the metamodel by specializing the existing metaclasses (middleweight extensions)
• using package merges to select the parts of UML you need (heavyweight extensions)

Each option has its own strengths and weaknesses, as you can see in the referred article/presentation. At this time, the TextUML notation supports two of those approaches: profiles and metamodel extensions.

Adding closures to UML

Even though profiles are the most popular (and recommended) mechanism for extending UML, it is not enough in some cases/applications. That has been the case in the TextUML Toolkit, for instance, when implementing closures in the TextUML action language (yes, the Toolkit eats its own dog food).

According to the wikipedia entry, “a closure is a function that is evaluated in an environment containing one or more bound variables. When called, the function can access these variables. ”

It really makes sense to (meta) model a closure as some kind of UML activity, which is basically a piece of behavior that can be fully specified in UML. Methods, for instance, are better modeled in UML as activities. Activities are composed of activity nodes and actions, which are similar to blocks of code and instructions, respectively.

The only thing that is missing in the standard Activity metaclass is the ability for a closure to have an activity node from another activity as context, so it can access context’s local variables. So here is a possible (meta) modeling of closures in UML using the TextUML syntax:

[Standard::Metamodel]
model meta;

apply Standard;

(*
  A closure is a special kind of activity that has another
  activity’s activity node as context. A closure might
  reference variables declared in the context activity node.
*)
[Standard::Metaclass]
class Closure specializes uml::Activity
  (* The activity node that provides context to this closure. *)
  reference contextNode : uml::StructuredActivityNode;
end;

end.

Or, for those of you who prefer a class diagram (courtesy of the EclipseGraphviz integration):

Note a model contributing language extensions must be applied the Standard::Metamodel stereotype, and each metaclass must be assigned the stereotype Standard::Metaclass.

Of course, there is no point in being able to metamodel closures, if there is no way to refer to them. We need a kind of type that we can use to declare variables and parameters that can hold references to closures. That also means we need to be able to invoke/dereference a closure reference, and there is no support for referring to metamodel elements in the UML action language. That means we need more language extensions. But I will leave that to another post. My goal here was to show how simple it is to create a simple UML metamodel extension with the TextUML Toolkit.

What about you, have you ever needed to extend UML using a metamodel extension? What for?

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)

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):

• automated tests (180 and 185)
• parser and model generation (181, 184 and 186)
• textual renderer
• editor

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.

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):

• automated tests
• parser and model generation
• textual renderer
• editor

Any other UML feature you would like to see exposed in the TextUML notation? Suggestions are welcome.

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.

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.

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:

• classes and structural features
  
• packages, imports, profiles
• associations
• multiplicity
• template classes

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.