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[ECore] How to reference fixed Ecore classes as well as model instances [message #659353]

Sat, 12 March 2011 17:04

Glenview Jeff

Messages: 79
Registered: September 2010

Member

I ran into what I believe may be a limitation of Ecore. I want to be able to define a metamodel with fixed set of datatypes as well as a reference datatype that references existing classes. My metamodel would look like this ideally (hopefully my pseudocode is readable.)

Metamodel:
  RootEClass: EClass
    xClass: 0..* Containment=yes
  
  xClass: EClass, xType
    xField: 0..* Containment=yes

  xField: EClass
    xType: 1 Containment =no

  xType: EClass

  StringType: xType
  IntType: xType

The problem with the above strategy is that in the model, I can't set a field's type to StringType or IntType since they haven't been instantiated in the model. I can only set a field type to whatever xClasses have been instantiated in the model.

I of course could do it as they do in the xpand sample project, where you create types in your model, but I think this is a poor design choice. I think that the data types should be fixed in the meta-model, not in the model.

The other way I thought to do it is to have an enumeration to refer to the fixed types, int, bool, etc., and one special enumeration that's called a reference. Then I'd have to have a separate field in the xType that's actually a reference. This is also quite ugly.

It is possible to accomplish this in Jetbrains MPS (see this tutorial.) Is there a similar mechanism I might be missing available in Ecore?

Thanks!
Jeff

[Updated on: Sat, 12 March 2011 17:05]

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Re: [ECore] How to reference fixed Ecore classes as well as model instances [message #727419 is a reply to message #659353]

Wed, 21 September 2011 09:04

Peter Saunders

Messages: 30
Registered: July 2009

Member

glenviewjeff wrote on Sat, 12 March 2011 12:04

I ran into what I believe may be a limitation of Ecore. I want to be able to define a metamodel with fixed set of datatypes as well as a reference datatype that references existing classes. My metamodel would look like this ideally (hopefully my pseudocode is readable.)
Metamodel:
  RootEClass: EClass
    xClass: 0..* Containment=yes
  
  xClass: EClass, xType
    xField: 0..* Containment=yes

  xField: EClass
    xType: 1 Containment =no

  xType: EClass

  StringType: xType
  IntType: xType
The problem with the above strategy is that in the model, I can't set a field's type to StringType or IntType since they haven't been instantiated in the model. I can only set a field type to whatever xClasses have been instantiated in the model

I'm looking at a similar problem at present. As an example, consider a model that describes books and colors. Each book has exactly one color. Some common colors must be pre-defined ("red", "blue", ...), but some colors will be defined by the user.

Is is possible to use ECore to specify a class that will be instantiated at the time that the root class is instantiated? If not, what is the best way to define this sort of model using ECore?

Peter

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Re: [ECore] How to reference fixed Ecore classes as well as model instances [message #761425 is a reply to message #727419]

Tue, 06 December 2011 13:14

Algar fr

Messages: 19
Registered: December 2011

Junior Member

Any solutions to this problem?

It seems exactly the same as the problem I have commented in this other post:
eclipse.org/forums/index.php/t/263531/

I will really appreciate any help about it.

PS: Sorry for the relative link. I cannot use URLs as I haven't reach 5 messages... Sad