[news.eclipse.modeling.mdt.uml2.ocl] Re: Built-in validation for read-on

["Christian W. Damus" <cdamus@xxxxxxxxxx>]

Interestingly, the spec also has this to say (p. 129) on the subject of
read-only properties:

    If a navigable property is marked as readOnly, then it
    cannot be updated once it has been assigned an initial
    value.

This allows the possibility of non-derived read-only properties.  These
would usually be initialized, I except, by an "init:" expression specified
in OCL.

Cheers,

Christian


Christian W. Damus wrote:

> 
> Hi, Andy,
> 
> This is Property constraint [6] on p. 127 of the UML2 2.1 specification.
> 
> The specification doesn't discuss the reason for this at all, but I would
> guess that the reason is that it isn't possible to read a non-navigable
> property (that is why it isn't navigable), so it would not make sense to
> indicate that it can only be read.  A non-navigable property wouldn't be
> writable, either.
> 
> isReadOnly in UML means that the property "may only be read, not written"
> (p. 125).  It does not necessarily indicate that the value is derived
> (which I think is what you mean by volatile).
> 
> HTH,
> 
> Christian
> 
> 
> Andreas Maier wrote:
> 
>> Hi,
>> in our CIM mapping to UML, we are mapping the Write qualifier in CIM to
>> the isReadOnly UML attribute. In CIM, associations have ends that do not
>> have the Write qualifier set. This consequently results in UML
>> association ends that have isReadOnly set to true.
>> 
>> When I run model validation, the following built-in validation rule pops
>> up due to this:
>> 
>> Non-navigable property '<<property_Constraints, cIM_Reference>>
>> <Property> UserOfService : CIM_LogicalFile [0..*]' is marked as
>> read-only.
>> 
>> It may be that the semantics of writeability is slightly different
>> between CIM and UML. In CIM, it means that a client application should
>> expect to be able to modify the property value.
>> 
>> My questions are:
>> 
>> - What is the purpose of this built-in validation rule ?
>> 
>> - What is the exact semantics of isReadOnly in UML ? (i.e. unmodifiable
>>    vs. not volatile)
>> 
>> Andy