Re: [boost] Feature Model Diagrams in text and HTML

From: Beman Dawes (bdawes_at_[hidden])
Date: 2001-06-06 14:49:00

At 05:07 PM 5/30/2001, Vesa Karvonen wrote:

 >I like the idea of expressing feature models using a language that is 
more
 >suitable for textual representation. Unfortunately I find it difficult to
 >express some feature models using the grammar described on the Boost site
 >http://www.boost.org/more/feature_model_diagrams.htm).
 >
 >What is the recommended way to represent a node with both mandatory and
 >optional features? For example:
 >
 >    concept
 >        |
 >        +---* mandatory_feature_a
 >        |
 >        +---* mandatory_feature_b
 >        |
 >        +---o optional_feature_a
 >        |
 >        +---o optional_feature_b
 >
 >Assuming that I understand the grammar correctly, the closest that I can
 >come to is:
 >
 >    concept
 >        ( mandatory_feature_a
 >        , mandatory_feature_b
 >        , optional_features
 >        )
 >
 >
 >    optional_features
 >        [ optional_feature_a
 >        + optional_feature_b
 >        ]
 >
 >As you can see, I had to introduce a dummy "optional_features" node. The
 >above two feature models are no longer technically the same.
 >
 >Have I misunderstood the grammar or is this a weakness of the grammar?

Perhaps you misunderstood the grammar.  In particular, note that "element" 
is allowed to be "details" which in turn may be an optional "feature-list".

The example you give should thus already be valid:

     concept
         ( mandatory_feature_a
         , mandatory_feature_b
         , [optional_feature_a]
         , [optional_feature_b]
         )

Perhaps it is confusing that the following are equivalent:

     concept [ feature_a, feature_b ]
     concept ( [feature_a], [feature_b] )
     concept ( [feature_a, feature_b] )
     concept ( [feature_a] + [feature_b] )
     concept ( [feature_a + feature_b] )

The first form would be eliminated if the second line of the grammar was 
changed to:

     feature  ::= feature-name [ "(" feature-list ")" ]

But I'm not sure it really matters.  In theory it would be nice if there 
was a single canonical form.  Any ideas?

Thanks for the interest.  Feature models are really useful, and having a 
language that allows them to be expressed as text still seems worthwhile to 
me.

--Beman