[news.eclipse.modeling.mdt.ocl] Re: custom operators and functions using

[Ed Merks <Ed.Merks@xxxxxxxxx>]

Guys,

Comments below.


Ed Willink wrote:
> Hi Elio, Ed
>
> [Ed: you may be able to provide a simple solution for b).]
>
> a) parser modification
>
> The parser is intended to be extended rather than modified. Be very 
> wary of modifying; you will have te re-engineer each time MDT-OCL 
> improves. That said we are in the process of migrating from LPG 1 to 
> LPG 2,
> https://bugs.eclipse.org/bugs/show_bug.cgi?id=242153, which will 
> require about four trivial edit procedures to existing extensions.
>
> b) operators
>
> In your Ecore model of custom data types (EClass not EDataType) you 
> can add operations such as "+", which you can then use them naturally 
> in OCL. Unfortunately these give a validation error in EMF so you 
> cannot genModel them.
>
> I'm not sure if the situation is any better for a UML model.
>
> This is a spelling problem I've been considering already: For OCL it 
> must be "+" for Java it must be perhaps "_plus". (OMG) OCL needs to 
> specify an encoding scheme for awkward characters and to specify a 
> concrete syntax access scheme. MDT-OCL supports access via double 
> quotes e.g:
>
> def: "+"(d : Date) ...
>
> I'm afraid I don't know of any solution to making Date + Date work today.
>
> The XSD support for EMF provides a form of renaming. I've copied this 
> to Ed Merks who may be able to explain how it could be exploited.
I'm not sure most of these types make sense to support addition.  I 
think it makes sense to add a duration to a time or a date, but not to 
add two times or two dates.  I imagine the support for such things would 
be done in the same way one would support BigDecimal or BigInteger.  I'm 
not sure how OCL supports operators on custom EDataTypes or even if it 
supports all the EDataTypes in XMLTypePackage; supporting all those 
would provide support for all schema-based models...
> c) call path
>
> I'm not very familiar with the EvaluationEnvironment, so nearly all of 
> what I'm about to suggest may already be the current MDT-OCL 
> functionality.
>
> You can introduce a derived LOTREnvironment which is created at each 
> stage of evaluation, with a reference to its outer context. At any 
> point these references give you the call path. You can then add custom 
> methods to evaluate any function of the call path that you like. 
> Perhaps you encapsulate these all in a richer Environment object and 
> implement just a single .oclEnvironment() method to access it. If you 
> get this working it might make for a useful contribution to MDT-OCL 
> and a submission for a future OCL specification.
>
>     Regards
>
>         Ed Willink
>
> Elio Damaggio wrote:
> > Hi all,
> >
> > I am modifying the OCL parser/evaluator in order to (besides other 
> > things):
> >
> > * include a series of time related datatypes (Date, Time, Duration, 
> > Timestamp). These datatypes should have standard infix operators (+, 
> > -, ..) like integers and so on... I think I have to modify the 
> > EvaluationVisitor. Is this the best course of action?
> >
> > * include predefined methods that, if applied on an attribute, have 
> > access to the model information of that attribute (i.e. which class 
> > they belong, in addition to the actual instance).
> > For instance, lets assume book have an attribute called author. And 
> > the "LOTR" book instance has "Tolkien" as its author attribute. Then 
> > the predefined method LOTR.author.info() should be able to know that 
> > it is invoked on the "author" attribute of a "book" class.
> > Do you have any idea on how to implement these methods?
> >
> > Thank you all,
> >
> > Elio