The Hello World sample is a nice starting point to show the syntax and capabilities of every new language. This test is also useful for code generators and Domain Specific Languages (DSLs) also as a proof of concept.

Following this honorable tradition, I have created a video showing the capabilities of Essential: the tool I am working on for doing agile Model Driven Development.

In this 10 minutes video you will get a general idea of the DSL the language provides to create:

• metamodels
• models
• templates
• and control transformations

In order to see the details, jump to Vimeo, activate the High Definition mode (HD) and set full screen (sorry embebed version is not good enough).

Essential IDE – Hello World sample from Pedro J. Molina on Vimeo.

More info about it and 12 usage scenarios in the last Code Generation 2010 presentation about Tailored Code Generators.

Share your impressions!

It also was the public presentation of Essential: the tooling supporting my approach for applying MDD. I got a very good feedback from the audience and receive many request to test the tool.

People interested in beta testing it can still enroll here.

Essential

To celebrate this milestone and give the chance to have more people trying it, an early version is going to be released for the people interested in.

If this is your case, please enroll yourself using the evaluation request form.

After presenting the metamodel DSL, today is the turn for the modelling DSL.

As commented previously, Martin Thiede has a nice prototype called Concrete of a Web editor for model and metamodels. Such work and video also helps to understand the modelling and metamodelling duality.

Coming back to Essential, our tool is also providing a DSL to instantiate a metamodel. But a sample will probably be more illustrative:

Suppose the following simple metamodel:

namespace Core.Class
{
    class ClassModel
    {
        composition List<Class> Classes opposite Model;
    }
    class  Class
    {
        string Name;
        composition List<Attribute> Attributes;
    }
    class Attribute
    {
         string name;
         string Type;
    }
}

You could consider it as a very basic OO model. Intentionally I haven’t added too many details to keep it simple.

If you continue building it; adding operations, arguments, association support and more… at the end, you can have a metamodel comprising a full class diagram of UML, for example. The complexity of the metamodel you want to use is up to you. Having the control of the concepts inside the metamodel you can always add or remove features.

Modelling tools focused in UML, for example, provides this metamodel closed. You can’t change it, it’s a hard-wired standard and you are not allowed to change the core directly (only by extensions points like stereotypes and profiles).

Modelling Language

Now, let’s see how we can create a model using the previous metamodel:

using Core.Class;
namespace MyModel
{
    ClassModel  myClassModel
    {
        Classes = [Customer, Invoice];
    }
    Class Customer
    {
        Name = "Customer";
        Attributes = [Name, Surname];
    }
    Attribute Name
    {
        Name= "Name";
        Type= "string";
    }
    Attribute Surname
    {
        Name= "Name";
        Type= "string";
    }
    Class Invoice
    {
        Name = "Invoice";
        Attributes = [
            Attribute Amount
            {
                Name= "Amount";
                Type= "decimal";
            },
            Attribute InvoiceDate
            {
                Name= "InvoiceDate";
                Type= "date";
            }
        ];
     }
}

In the sample, a basic declaration of two classes (Customer and Invoice) has been instantiated using the concept Class defined in the metamodel. Each metamodel concept is instantiated using it as you would be using a class in Java, C# or C++. Properties are assigned in the natural way one would expect in such languages.

As expected, the using operator imports the metamodel to be employed.

In the lines 26-37 you can see how properties can be also defined inline for list contexts.

Under the curtains, the tool is providing code completion, syntax colorization, error management and real-time parsing as you could expect from a modern IDE.

Essential uses DSL text for serialization but also XML can be derived. This XML document is conformant with an XSD derived from the corresponding metamodel.

Intended usage

Consider now, a basic DB metamodel:

namespace Meta.Database
{
    class Schema
    {
		string Name;
		composition List<Table> Tables;
    }
    class Table
    {
		string Name;
		composition List<Column> Columns;
    }
    class Column
    {
		string Name;
		string SqlType;
    }
}

With this base in mind, you can define a business model containing (Customers, Invoices, etc.) based on a class metamodel and then, look for ways to transform your class model in, for example, a DB model representation. This is called, a M2M transformation (Model to Model). Essential will provide specialized languages to do that.

After that, your derived DB model can again be generated to final code, for example SQL DDL scripts in a given certain dialect. This is generally called a M2T transformation (Model to Text) and again Essential provides tools to describe the transformations.

Basically, to complete all this stuff, we need to introduce two more specialized languages: one for applying transformations, and another one for templates to be converted to final text.

I will focus on templates side on the next post.

The first one is related to Enterprise Architecture. The second one is a tool for applying MDD. Both projects are not related in any way. But it’s curious how we collide choosing the same name.

I don’t want to confuse people and fortunately the name is not the key part of our work. So, probably, a rename for our side (as the newcomers) would be gentle an a good choice. I’m open to suggestions for a new name.

In my previous post, I introduced Essential, a custom-developed tool for doing Model Driven Development.

As promised, in this post I will describe the primitives of the first language of the tool: Essential.Meta. This meta-language is helpful to describe the structural aspects of a metamodel.

The input requirements for the language are:

1. Usable for meta-structure description
2. Human readable/maintainable
3. Concise as possible
4. Easy to understand
5. Object oriented
6. Technology agnostic
7. Textual
8. Extensible
9. Scalable
10. Reusable definitions

Ok, that was the initial wish list. Now, let’s review how we can cope with it and show a short example of how it looks like:

namespace Meta.TownModel
{
    enum Sex  {  Male, Female }

    class Town
    {
        string Name;
        List<Person> Habitants;
        composition List<House> Houses;
    }

    class Person
    {
        string Name;
        string? MiddleName;
        string Surname;
        Sex Sex;
        int? Age;
        List<Person> Children;
        House Home;
    }

    class House
    {
        string Address;
        composition List<Room>0..* Rooms opposite 1..1 House;
    }

    class Room
    {
        string Name;
        decimal? Dimensions;   //In square meters
    }
}

The sample describes a meta-model for describing a town, with its buildings (houses) and inhabitants (persons). Nothing complex, nothing weird if assuming I am using a C/C++/Java/C# syntax and this doesn’t suppose a problem for you. I selected a C-like syntax instead a Pascal or VB flavour due to its less verbosity and a probably biased to what we used get to.

The namespace defines a scope for naming. All of our definitions are enclosed in a namespace. Therefore names of concepts should not collide inside a namespace. Same names are allowed in different namespaces.

As you can see, the main concepts in this language are classes and enumerations.

Enumerations define closed sets of named values helpful to describe domains. Classes on the other hand, have the classical meaning and properties or attributes can be defined for each class.

As usual in object languages each property has a type that could be primitive, an enum, a class type or a composed type.

The primitive data types supported are: string, bool, int, long, decimal, char, date, time & datetime. That should be more than enough, for the moment.

A note to readers: data types here are platform neutral, they are not java string for example, neither a C# string. It was horrible for me to see in a lot of diagramming UML tools whose names I will not cite, early mapping types to implementation languages like java:string and similar things… I sure you understand me. Such feature could be nice if you are doing reverse engineering or documenting code (a bit late BTW). But definitely horrible to see when doing conceptual modelling and haven’t chosen yet the final implementation platform.

Another relevant feature of the language is the cardinality operators. Each property has a cardinality attached to it. Following a Convention over Configuration approach, simple properties like string Name; has an implicit cardinality 1..1. You can also write to make it explicit in the language: string 1..1 Name;

List of things, on the contrary has an implicit cardinality of 0..* (zero to many). However you can further constraint it to 1..* (compulsory multi-valued) or arbitrarily to any pair of minimal and maximal values List<Holes> 18..24 GolfCampHoles;

The next feature to review is the composition keyword. A composition indicates that the property can’t exist alone, without its container. If the container is destroyed, the composed children will disappear also. Containment should be unique for each object; it cannot be contained in two direct containers at the same time. However, transitive containment it’s allowed.

There are some times, when we will be interested not only in one side of the relation between two classes, but also in the others’ end. That’s the case of the Children property. How about reaching the parents? To express it, the language introduces the opposite keyword. In our small sample it can be fully expressed (cardinalities included) as:

List<Person>0..* Children opposite 0:2 Parents;

Make sense, isn’t it? A person can have 0 or many children and let’s say zero, one or two well known parents.

I am still considering if the keyword List<T> could be also removed from the language. One can argue that cardinalities can be more than enough to express the same. However, I am still considering including other composed ADTs (abstract data types) in the future like Set<T> or Stack<T> to cite some of them. So, doors are still open to reconsider it.

Another feature we wanted to add is extensibility: If you are using this metamodel but needs to extend it for your own needs, the language is prepared to allow it. Just add another definition like this in another file and you got it:

namespace Meta.TownModel
{
    class Town
    {
        Person Mayor;
    }
    class Person
    {
        List<Person>0..* Friends opposite 0..* Friends;
    }
    class City : Town   //<--Inheritance sample
    {
        //extra city properties…
    }
}

Now, your town must have a mayor and persons can have friends!

The language allows partial definitions in the same or different files. If the namespace and class name matches, the properties of the Town class and Person class are extended by merging partial definitions.

From the cardinality point of view, Friends is a curious symmetric relation. It is a many-to-many relation but both ends  (the roles) are normally called Friends and not: MyFriends and OthersGuysConsideringMeAFriend but how knows! }:)

As briefly seen, this language is useful to impose rules over data. It constrains the objects/concepts we can describe and the allowed properties.

Intended usage

OK. Some of you are probably thinking: and what in hell it this useful for?

The mail goal is to use the language to describe the domain in which we are planning to apply MDD. With this description, we will describe the concepts, properties and relations of the problem domain we are interested in.

If you are really, really pragmatic, and the analysis and design of the domain for the joy of it doesn’t satisfy you, well, consider then that we can derive (manually or better 100% generated if you prefer) some other interesting and more earthly artefacts:

1. UML class models (structure), XMI, etc.
2. XML Schema (XSD),
3. SQL Schema (relational tables to persist the data),
4. Classes in Java (POJOs), C# (POCOs), or any other language implementing a pure Domain Model
5. XML de/serialization code to read/save XML documents been conformant with (2)
6. Data Access code (DAO) to connect (3) with (4).
7. Maps to your favorite ORM tool to connect again (3) & (4)
8. Etcetera, see Domain Driven Design and other approaches.

That’s all for today! This was the first DSL implemented in Essential targeting metamodeling. For more details, a full reference of the Essential.Meta language is described here.

On the next post, we will talk about a second DSL in Essential: the model (object level) language used to instantiate the concepts we just have created.

Thanks for reading! And please share your thoughts about it!

A title like this could sound utopian and probably it is in the extreme, but at the same time provides two advantages:

1. a suggestive title brings more blogs readers , and
2. these kind of Quests keep me active developing and testing my ideas about MDD.

Sorry for 1, the joke. But Let me explain 2 a little further if you are interested:

Some months ago, I started to develop a new tool for doing Model Driven Development. I always start new developments with contained expectatives. I consider most of them throw away propotypes just to test a new way of doing the same thing, but luckily, with less effort and better productivity. But when you found the way, you follow it again whenever you need it, isn’t it?

So, this time is one of those moments: I am quite happy with the results, and I will continue building on the top of it to make it grow.

Today (almost?) everyone agrees on code generation can make your life notably easier as long as you have:

1. a stable domain,
2. a clear knowledge of your domain (domain expert) and,
3. tools: modelling editors, model checkers, and code generator adapted to your domain and your chosen target architecture and language.

The trickiest one to get is, not surprisingly, the third one. And this issue: the quality and the applicability of the MDD tools is the main stopper when considering applying MDD for a software development project.

So, my motivation during years is not only to create code generators one more time, but do it in a way that it will be cheaper to obtain results in next projects. Therefore, reducing the requirements for the entry level will help the MDD adoption to gain speed.

Ok, wait a minute, are you reinventing the wheel again? Building another meta-code-generator?

Yes I know, there are very good and mature tools for doing MDD: such as EMF/GMF, XText, ATL, TextUml, Metacase, MS DSL Tools, etc.

However, guided by my intuition and the experiences in the domains I have worked in, I have a strong opinion on of how some things should be done and for the moment I didn’t found the perfect tool to satisfy my needs.

But, instead of complain, I decided to take to the action and add my two cents implementing my view about MDD tool support: taking the good ideas of the standards available and reinventing the parts that don’t fit.

The tool

After this introduction, the name of the tool is not going to surprise you. It is named Essential.

The goals of the project are following ones:

• to declaratively describe metamodels, models, templates, and transformations using textual DSLs
• to provide a comfortable editor for each of these four pillars,
• to provide model checkers to assure the integrity of the four, and
• to build code generators and transformation interpreters to achieve the output we are looking for.

In the next posts I will depict the DSLs used in Essential and some architectural choices. This will help us to discuss the essence of the problems found in MDD.

I want to thanks Javier Hernandez for his constant help, good discussions and counterpoints about choosing design alternatives for Essential. And also to Nicolas Cornaglia and Ángel Marín for their active beta testing as early adopters and providing good test fields.