Re: [Cbor] CDDL Module Design

[Michael Richardson <[e-mail]>]

Jim Schaad <[e-mail]> wrote:
    > 1.  What is the naming scheme to be used?  Both XML Schema and ASN.1 use
    > unique identifiers for a module.  The problem with this approach is that a
    > revised module has a new identifier even if all of the changes were
    > preserving of the old module.  This can also present problems if two
    > different versions of the same module are used as it can be difficult to
    > know which version of a module is being provided.

Doesn't the version problem also include the "DLL hell" problem?
That is:
     module A includes module B.1 which includes C.1
            A includes module D.1 which includes C.2

and who knows if C.1 and C.2 can be used at the same time?

So I totally agree that this is a problem.

    > I think therefore it
    > would be nice to have a naming system that recognizes version numbers, but
    > can be used with a "latest version" mode.  One possible way to do this would
    > be to use a query parameter to get a specific version of a module while
    > without the query parameter the compiler grabs the most recent version it
    > has.

I think that this is probably a very elegant solution.

    > 2.  Do want the naming scheme to be used to access a module name from the
    > web, and to create a server to host all of the IETF based CDDL modules?

A think that I dislike about the ENTITY stuff in XML is that the URLs are way
too specific.   Do you want avoid that?  Will it be some URN space?

    > 3.  For any number of reasons we need to be able to state that some symbols
    > are going to be imported from a different module.  There are some issues
    > around doing a couple of other things:
    > *  If all symbols are imported then you either need to have a module based
    > naming system or you need to ensure that there are no collisions.
    > *  If only specific symbols are imported, then they could either be a) made
    > to be unique by renaming or b) made to be unique in the current module
    > simply by how the module is written

Can you give an example of (b)?
I think that Python mostly got this process right.

    > 4.  ASN.1 has a method to say that only specific symbols can be exported
    > from a module.  I have never used this capability and I am not clear that it
    > would be useful to have here.  Should we support it anyway?

No. It just leads to stupid work arounds.
_ for things that should not be exported, but not enforced.

    > 5.  How should the system be setup to be able to recognize this capability.
    > The suggestion in the freezer document currently is to use a pragma system.
    > Introducing a pragma system can easily be seen as a step to allow for
    > compilers of CDDL to be written.   The A2C compiler that I wrote used --#
    > and #-- as the start and stop delimiters for pragmas as "--" is the
    > start/stop comment character.  (ASN.1 is not line based so there is no
    > comment till a return.)  A similar approach can easily be used here.

I prefer that the statement not be a pre-processor-like hack.

    > 6.  If we use a pragma naming system, do we want to setup in advance for it
    > to have namespaces so that a single module could be used with different
    > compilers.  I ended up using a different string  than the OSS compiler did
    > ("--<" ">--") to be able to do this but having a namespace could also
    > support this.

I don't understand.

    > 7.  What set of pragmas are we looking at to start with.  XML Schema has
    > some attributes that can be used for controlling the compiler.  One of this
    > is a location hint attribute which can be used for giving alternate
    > locations to use for finding a module (such as a location on my machine).
    > There might be some other pragmas that might be useful to specify as well.
    > It might be easier to specify co-occurrence constraints using pragmas rather
    > than trying to put it directly into the language.

This is useful at the top-level file.
Particularly for a group of people who are working together.
For "location on my machine", I think that I'd rather be providing a command
flag, but I don't object to having ../.. paths or
https://my.little.server.example/ in a file.

--
Michael Richardson <[e-mail]>, Sandelman Software Works
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