Re: gEDA-user: Light? Heavy? Reuse...

[DJ Delorie <dj@xxxxxxxxxxx>]

> It seems to me you're arguing for a plugin mechanism for gnetlist,  
> too.

Perhaps, or something more global.  I.e. it would be nice if you
*could* query these extra databases from within gschem or gattrib, for
example, to see what the inferred attributes are, or to see what the
options are so you can explicitly set something.  For example, if you
specify a 1k resistor, it may give you a choice of 0603 or 0805
footprints.  By choosing one of those, you've helped direct gnetlist
towards a specific part and the extra attributes that go with it.

So the two types of "plug-ins" would answer these questions:

1. Given the attributes the user has already specified, what other
   attributes may be set and to what values?

2. Given a set of specified attributes, what other attributes are
   needed, and can we infer the values of those attributes, either by
   process of elimination or by project-specific defaults or rules?

The second needs the first, of course, but both should be available to
more than just gnetlist.

> Right now, gnetlist merges netlists and attributes extracted  
> from gschem schematics, and then passes that information to a "back  
> end". But why not allow multiple front ends? Merge information from  
> multiple formats into the data structures. Then allow "filters" to  
> work it over: that's where one might implement a "requirement to BOM"  
> process. Finally, pass that to the back end as now.

Certainly a good idea, except that it doesn't offer a way to feed-back
to gschem for things that the user *must* (in their opinion) select.
For example, what resistor values are available?  In what tolerances?
If you pick a 10uF capacitor at 10v, what's the smallest package it
comes in?  Like I've said before, the schematic is more than topology
- it's design.  Some attributes are intrinsic to the design, like
resistor/capacitor values, and should (according to some folks at
least) be included with the schematic.

The extra database contains (or could contain) all this information.
It's up to the user to specify *enough* attributes to uniquely
identify a specific physical part (in the pcb case at least), or in
combination with a BOM tool or preferences ruleset, at least be able
to pick something appropriate.  However, IMHO the user needs access to
these attribute options in gschem.  They may not always use gschem for
this; there's no reason why the choices or rulesets can't go
elsewhere, but a goodly chunk of our userspace will want a way to
choose such things right in gschem.  Especially if one of the
attributes is "value" :-)

The key to heavification is that some of the inferred attributes
include the pin name-to-number mapping.  This lets you use really
light symbols without the "transistor problem" we currently have.  But
even then, users may want to direct this slotting from within gschem.


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