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Date:	Tue, 22 Dec 2015 13:30:15 +0000
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Subject:	Re: [geda-user] Cross project collaboration on data models
From:	"Peter Clifton (petercjclifton AT googlemail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To:	gEDA User Mailing List <geda-user AT delorie DOT com>
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Hi Nicklas,

What you appreciate about gEDA is one of its fundamental early design
choices (way back before my involvement in the project), and one of
the strongest aspects which makes gEDA what it is. I am not trying to
change this - and it would be an aspect of any cross-tool open EDA
data-model we would have to ensure was represented in order to fit
gEDA's needs.

I'm perhaps focusing a more on the PCB side (where our existing
data-models and file format most often causes problems),

PCB often bumps into limitations with its file-format not expressing
certain design aspects / concepts, and often needs to be extended in
an ad-hoc way. One key aspect I need to get in at some point - is that
of a mechanical outline.. which is one of the key missing pieces
holding back my 3D board export code from moving upstream. (My
test-code takes a guess based on some heuristics, after looking at the
outline layer, but this non-semantic data is a "bad idea", and not one
I'm prepared to push upstream).


One distinction to draw, is that data-model and file-format are two
distinct topics. They are very much related, but - for example, one
could have multiple file format which all represented information
according to a common model. In the case of my mechanical outline,
this is very easily modelled by the software (as a polygon
representing the board shape), but no file-format to load/save it
exists yet.

A more complete treatment of board shape might require a more complex
models.. take for example a flex circuit - where the board can have
different shapes per layer. There are a lot of situations to handle
correctly - and ideally, in a forward compatible way (or get it right
first time!).


To take another PCB example - lets say pad-stacks. Some CAD systems
define these explicitly, and reference those from the board design,
footprints etc.. gEDA/PCB does not, it stores (rather limited)
information about pad geometry in-situ, for each pad instance, for
each component instance in the design. Our data-model has no concept
of a referenced pad-stack, which means it is not convenient to make
mass changes to all instances of a particular type of pin/pad/... on
the board. (Software would need to pattern-match / guess which pads
are supposed to be the same - no semantic information exists).


Peter



On 22 December 2015 at 13:03, Nicklas Karlsson
(nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]
<geda-user AT delorie DOT com> wrote:
>> I think this is of critical importance to allowing a (currently) smaller
>> player like gEDA to survive amongst more successful / active projects.
>
> Only reason I used gEDA is because of thin bindings which allow to start with a simple sketch without all details and fill in more information then needed. Start of a new circuit is usually a simple sketch or block diagram altough some components only have one order number others like capacitors,resistor have diferrent values,sizes and order number may be the last step or may even change after board have been delivered.
>
> If it is possible to use fileformat from other software I however think it is a good idea. To copy some other software I think is rather pointless because in such I would be better of start using it directly.

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