Re: gEDA-user: multiple attributes (was: [Patches] GTK Recent-file-manager)

[John Doty <jpd@xxxxxxxxx>]

On Jan 4, 2011, at 6:04 PM, Peter TB Brett wrote:

> On Wednesday 05 January 2011 00:42:07 John Doty wrote:
>> On Jan 4, 2011, at 5:22 PM, Matthew Wilkins wrote:
>>> What are typical use cases for having multiple same-named attributes in a
>>> symbol?
>> 
>> A slotted symbol generally needs multiple slotdef attributes.
>> 
>> A hierarchical symbol will have multiple source attributes if its
>> underlying schematic has multiple pages.
>> 
>> And nobody knows what other use cases there are, or may be in the future.
>> You should make as few assumptions about how people will use attributes as
>> practical.
> 
> One of the problems we have at the moment is that sometimes attributes in the 
> schematic override attributes in the symbol, and sometimes they don't.
> 
> Example 1.  Suppose I have a "refdes=A?" attribute in a symbol. I instantiate 
> the symbol in a schematic, and attach a "refdes=A1" attribute to the 
> instantiated symbol.  gnetlist (etc) will use "refdes=A1".  This is overriding 
> behaviour.
> 
> Example 2.  Suppose I have a "net=Vcc:1" attribute in a symbol. I instantiate 
> the symbol in a schematic, and attach a "net=Vdd:1" attribute to the 
> instantiated symbol.  gnetlist will short Vcc to Vdd and connect pin 1 to the 
> shorted net.  This is aggregation behaviour.
> 
> The problem with this is inconsistency.  IMHO it would be better to have 
> overriding behaviour *only*, because in the longer term being able to reliably 
> override attributes would particularly be helpful in doing things like 
> hierarchical back-annotation and parameterised subcircuits (the latter would 
> be awesome for ASIC design applications, for instance).  As far as I can tell, 
> everything that can be achieved with aggregation behaviour can be achieved 
> with overriding behaviour, but not the other way around.

This sort of inconsistent behavior is a serious barrier to extension of capability. I agree with this diagnosis.

---
John Doty              Noqsi Aerospace, Ltd.

This message contains technical discussion involving difficult issues. No personal disrespect or malice is intended. If you perceive such, your perception is simply wrong. I'm a busy person, and in my business "go along to get along" causes mission failures and sometimes kills people, so I tend to be a bit blunt.



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