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Re: [emft-dev] [EMFatic] Alignment with OCLinEcore

Hi Sven

On 27/03/2010 22:52, Sven Efftinge wrote:
cool that you're implementing OCL in Xtext. We have similar plans for EMFatic. We're working on a base language for Xtext (called Xbase) which allows people to create new languages which extends and reused parts (or everything) of it. We want to implement an EMFatic editor based on it.

I find Xbase an interesting source of ideas, but not directly useful for MDT/OCL and I'm temporarily bypassing the generic types that Xtypes would solve. [I'm likely to have a GSoC student doing direct Java code generation from OCL. It would be good to align this to support an interchange point for alternate 'action' languages such as Xexpr.]

I find that OCLinEcore at the model level is OCL in Emfatic at the concrete syntax level so there will be duplication between the editor I'm committed to providing as an Example in Helios and Emfatic in Iona. Long term it presumably makes better sense for OCL to depend on Emfatic rather than Emfatic on OCL, so the functionality, if not the implementation, should migrate. However I'm not sure there is really any point in confusing users with both a traditional Ecore/Emfatic editor and an enhanced Ecore/OCLinEcore editor. So perhaps Emfatic should provide the combined editor exploiting EssentialOCL.xtext to provide the semantic validation of OCL expressions.

The OCL embedded in EAnnotation is persisted in concrete syntax form. The editor parses an OCL expression to a tree but has to fight Xtext to revert it to a String again. Xtext does not allow a non-trivial rule to return a String!

What persistent representation do you plan for Emfatic? Xtext does a very good job of hiding the XML representation, but the use of *.ecore is very entrenched, so I'm not sure that all *.ecore will migrate to *.emfatic.

I'm finding it not too hard to provide a variant DocumentProvider so that *.ecore is the persistent representation for OCL in Ecore. On load, the Document InputStream starts as the Ecore XML that is loaded as an Ecore AST and is then transformed to a similar CST which is serialised to provide the OCLinEcore InputSteam for conventional editing. On save, the CST is transformed back to the Ecore AST which is saved.

The 'similar' CST is needed to make the serialiser work on Ecore. It solves simple problems such as:
'readonly' is inverted from EStructuralFeature.changeable
'ordered' is default not-ordered in CS but default ordered in Ecore
multiplicity has '*' representation for upperBound -1, and also '?' short forms
embedded OCL annotations need first class representation
other annotations need a representation

[The serialiser seems quite slow. A direct Java implementation seems attractive if the XML input is common and would not have such struct exact-serialisability constraints.]

Since both *.emfatic and *.ecore may co exist, the editor needs to support either on input, which is relatively easy with a "<xml?" peak. On save, the input format should be the default output, but the alternate should be selectable. More generally perhaps Xtext should always offer a SaveAs XML option.

In summary:

How would you like to progress the Emfatic-OCL dependency?

What persistent representations do you envisage for Emfatic?

[And how do you plan to persist Emfatic comments in a *.ecore?]


        Ed Willink

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