Re: OCL: dealing with exceptions



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From: Anneke Kleppe (A.Kleppe@klasse.nl)
Date: Wed 29 May 2002 - 08:36:43 BST


I understand the wish the express that exceptions are raised and under 
which conditions that occurs, and I'll do my best to get it in OCL. But 
again, we can not specify such a construct until the UML 2.0 and MOF 2.0 
Core packages are stabilized. It makes a lot of difference whether an 
exception is considered to be a classifier or not, and what raising an 
exception means in terms of the metamodel (is a new Exception object 
created, or are the attributes of an existing Exception object changed, is 
it an operation call on a metamodel object?), etc. etc.

I personaly find it very frustrating to have to wait so long before the 
core concepts are finalized, specially because the OCL 2.0 is finished but 
for the parts that need to be aligned. But there's nothing we can do. Maybe 
next week we'll know more.

Anneke

At 12:08 PM 28-05-2002 -0500, you wrote:
>Anneke Kleppe wrote:
>
>>The current status of OCL 2.0 is that it is aligned with the UML 1.4. As 
>>soon as the UML 2.0 submissions stabilize, we will align OCL 2.0 with UML 
>>2.0. As the core of the UML 2.0 is to be the core of the MOF 2.0 also, 
>>the alignment of OCL with MOF follows.
>>
>>Now to answer your question: no there is currently no explicit support in 
>>OCL 2.0 for these MOF exceptions. There might be later on, if during the 
>>alignment this proves to be an important issue.
>>
>>BTW, you say you are expecting it, but there have not been any requests 
>>to the OCL submission team to include this. Please tell us, if you want 
>>something in. We are only human, you know. :-)
>
>Well, I think it seems useful to be able to specify directly, in the 
>postcondition for an operation, what exceptions will be thrown under what 
>circumstances. In particular, I think that you would want to be able to 
>type-check something like this:
>    context Bank:deposit(x : int)
>    post: if x > 0 then balance = balance@pre + x else raised 
> DepositException end if
>
>The type-checker would type this postcondition as "boolean" since, if it 
>returns anything at all, it will return a boolean (like in ML). Your 
>examples type-check to boolean too. But, what if you want to say this 
>(admittedly, a contrived example):
>
>    context Bank::deposit(x : int)
>    post: let with-interest = if x >= 0 then x * sqrt(x) else raised 
> DepositException end if in
>            balance = balance@pre + with-interest
>
>Now, interest(x) has to type-check to a rational number. But, it isn't 
>clear to me how, using any approach, how I can express with-interest in a 
>type-safe manner.
>
>Even without the above, the examples cited still seem very awkward to use 
>in practice, compared to something like "raised" above. I think users of 
>UML/OCL would want a "raised" facility in OCL, especially for languages 
>like Java where exceptions are as much a part of the postconditions as 
>normal returns (i.e. you want to distingush between "undefined behavior" 
>and "exception XXX raised"). Perhaps the specifics of such a construct are 
>difficult to specify though?
>
>Thanks,
>Brian
>
>
>
>
>
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