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Re: Some additional obscure questions...Forward Refs



At 2/3/2003:04:10 PM, David T. Perkins wrote:

Hi Dave,

I didn't mean to pick a fight with you, Dave.
I'm just looking for some answers.

>1)Is support for forward references required in the MIB module language?
>The answer is "OF COURSE".

The question was
"Where is the requirement in the SMI to support forward references?"

[My copy of "Understanding SNMP MIBs" (1997) only shows one
entry in the Index for forward references and that is in the
part of the SMIC Appendix (C.12.7) that explains that SMIC
does not use a library of previously compiled MIBs to resolve
certain kinds of references.]

>2)Can a rule be made such that all OID values defined in a MIB
>module are "under" the OID value specified in the MODULE-IDENTITY?
>The answer is "OF COURSE NOT".

No need to worry about that.  The IMPORTS statement safely
handles any such requirements.

>3)Could a new language be specified that doesn't allow forward references?
>The answer is "OF COURSE".

The question was whether the current MIB module language
specifies a requirement for forward references?  To the best
of my (possibly faulty) knowledge, it does not and, furthermore,
does not need to.  So, there is certainly no need to define a
new language that specifically does not allow them.

>This is really old stuff. REALLY OLD.

Yeah, so am I...but I'm still trying to learn.

Thanks again for taking the time to give this query some
consideration.

Cheers,

BobN
- - - - -
>At 04:02 PM 2/3/2003 -0500, Bob Natale wrote:
>>At 2/3/2003:03:35 PM, David T. Perkins wrote:
>>
>>Hi Dave,
>>
>>>I think you are trying to change the point,
>>
>>You're right -- in an attempt to learn something
>>from you (and anyone else who cares to comment --
>>so I've modified the Subject header to reflect the
>>current focus.
>>
>>>which is that examples to demonstrate conformance are more powerful
>>>when they check all aspects of the conformance instead of the trivial
>>>case.
>>
>>True...but examples which demonstrate arcane scenarios
>>and/or non-standard/non-required features might contribute
>>more to confusion than to elucidation.
>>
>>>Of course,
>>>examples to "teach" about functionality would be written differently.
>>>And examples to show common practice would be different.
>>
>>True.
>>
>>>On the forward reference issue....
>>>First, forward references are a feature of ASN.1, and one that is
>>>carried forward to the MIB module language.
>>
>>Where is the requirement in the SMI to support forward references?
>>
>>>(And yes, supporting or not supporting forward references makes a BIG
>>>difference in MIB compiler design, including data structures and error
>>>detection and reporting!)
>>
>>Yes, supporting fwd refs complicates those aspects significantly.
>>Hence, one would want to be certain that doing so is required
>>by the applicable standards.
>>
>>>Second, someone would have to do all the work to determine if
>>>eliminating all forward references would create an undue hardship
>>>on writing (and reading) MIB modules.
>>
>>Are you suggesting none of the MIBs with fwd refs can be
>>compiled by any of the MIB compilers that don't support
>>fwd refs?  Or, would you say that those MIBs can normally
>>be compiled by such compilers with relatively modest editing
>>to the MIB source file?  Answering "yes" to the first question
>>seems impossible, given existence proofs.  Answering "yes" to
>>the second question indicates clearly that fwd refs are not
>>required in practice.
>>
>>>There is one place (not in the imports) that MIB compilers not
>>>supporting forward references results in pretty ugly MIB module
>>>specification. That is the OID value that is used for the value
>>>of a MODULE-IDENTITY construct.
>>
>>Given some standard root starting point(s) -- which we have --
>>there is no MODULE-IDENTITY value that could not be specified
>>directly as a successor to an IMPORTed value, I believe.  Am
>>I wrong about that?  Furthermore, IMHO, every MODULE-IDENTITY
>>value *ought* to be so constructed...first as a matter of
>>good design and second as a requirement (since I am currently
>>unaware of the SMI requirement to support fwd refs).
>>
>>As I said, I suspect I'll learn something from this thread!
>>(And thanks for taking the time.)
>>
>>Cheers,
>>
>>BobN
>/david t. perkins