Re: sppi EXTENDS and AUGMENTS clause

["Andreas Polyrakis" <apolyr@cs.toronto.edu>]

Ravi, 

thank you so much, everything seems much clearer now!
I will have a look at TagId and TagInstance, as you propose.

Thanks again!

Andreas




> Andreas,
> You would need to use EXTENDS in this case, since your 
> requirement is that, an instance of class A could be of 
> a part of an instance of class B OR C,
> ie B, C EXTENDS A.
> 
> You use AUGMENTS when you want to add attributes,
> to a previously defined class(A), such that for every 
> instance in A(the AUGMENTED class) you would have a 
> corresponding instance in B and vice versae(1-1 mapping). 
> In the EXTENDS relationship, an extended class(B) instance 
> would have a corresponding instance in the Base class(A),
> but the reverse doesnt hold true, since A may be EXTENDED
> to form another derived class.
> 
> Regarding your other question,
> when using EXTENDS, the index is controlled by the base 
> class. So, you can install/update an extended PRC instance,
> by sending instances of the extended PRC's with the
> index of the base instance as shown,
> < <base table entry OID>.X > < Encoding of base attributes >
> < <Extended table entry OID>.X > < Encoding of derived attributes >
> (X is an InstanceId )
> 
> Regarding your last question, The EXTENDS semantics do not
> allow more than one row in the extension class to be associated
> with a row in the base class. But This sort of grouping
> semantics IS allowed by the TagId and TagInstance Textual 
> Conventions, see section 8.11 in the SPPI. 
> 
> Ravi
>