Re: RFC: ppath(3): property list paths library

[David Young <dyoung%pobox.com@localhost>]

On Wed, Nov 03, 2010 at 05:57:39AM +0000, David Holland wrote:
> On Mon, Nov 01, 2010 at 08:00:09PM -0500, David Young wrote:
>  > I'm working on a library called ppath(3) for making property lists more
>  > convenient to use in the kernel.  With ppath(3), you refer to a property
>  > to read/write/delete in a property list by the path from the list's
>  > outermost container.  Comments welcome.
> 
> Speaking from the POV of someone who's been working on querying
> semistructured data for several years now... I have a pile of
> high-level questions: (1) can you articulate the expressive power you
> intend for your path expressions, and why that's a logical stopping
> point vs. more expressive things;

I want to index individual elements in a property list using succinct
and reliable C code.  Ideally, I would be able to treat a property
dictionary/array as a C struct/array and use an expression such as
"a[i].b.c.d[j]".

It's a logical stopping point because it meets my needs.

(2) what if any facilities do you
> envision for checking paths against proplist schemas when/if we ever
> manage to sort out a system for that;

None.

> (3) what model do you have for
> dealing with cases when the values found at the paths provided are not
> what the user is expecting; and

ppath(3) routines return EFTYPE if the application code tries to read
one type (e.g., bool) from a path and ppath(3) finds another (e.g.,
number) at that path.  Beyond that, it's up to the application.

> (4) what model do you have for dealing
> with cases where the path does not name a single unique value or
> position, if that's possible?

That's not possible.

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 278-3933