required vs optional

James Bonfield jkb at
Thu Feb 8 12:43:49 UTC 2001

On Thu, Feb 08, 2001 at 12:19:26PM +0000, Peter Rice wrote:
> If both are N, EMBOSS will not prompt. The application will always receive a
> value, and it can always be set through the command line.

I think this is where the confusion comes from. ACD is designed for command
lines where each question is presented one at a time, whereas I'm dealing in
GUIs where the questions need to be shown all at once. For added complexity
the users may answer questions out of order.

> > Can you please spell out for me exactly when we can be sure (during
> > processing, not just at the time of producing help) when we know a question
> > will be ignored (ie changing it's value has no effect)?
> You can't be sure - only the application code can tell you that.

So this is getting back to my original proposal. I'd come to the conclusion
that the required and optional attributes where not enough to indicate whether 
an application needs a value for an option. Hence the suggestion of an extra
attribute that indicates this (via an expression).

Without this I basically have to have all options permanently available to the 
user even though I know many are useless (eg the user has selected not to
perform a plot in pepwheel, but they are still asked to provide information
about how the plot should look). I know on a web-form there's nothing that can 
be done about such matters, but most real windows of unix applications do make 
use of greying out unneeded options so that the complexity to the user is

Would you have any objections to me making use of a needed: attribute?

> But you can be sure that the command line version will process everything in
> one pass so all the information is in the ACD file.

But above you indicated that some information is known only by the application 
and so it isn't in the ACD file.

> > (I have been wondering about an "optional" tab so that the option values are
> > automatically put into a separate area of the dialogue.)
> That is what we rather expected GUI developers to do.

The main problem is that the natural grouping is separated. Eg pepwheel -h
indicates that the options tab would contain how to plot the wheel, but
whether to perform the plot is in a different tab (advanced).

Also for syco -graph and -outfile are both listed as mandatory, and yet the
program will only ever use one or the other and never both (depending on the
advanced parameter -plot). This would be rather confusing to the user.


James Bonfield (jkb at   Tel: 01223 402499   Fax: 01223 213556
Medical Research Council - Laboratory of Molecular Biology,
Hills Road, Cambridge, CB2 2QH, England.
Also see Staden Package WWW site at

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