SXFM is for Simple XML Feature Model format.

The major advantage of this format is that one can create feature models using a simple text editor. As a consequence, SXFM models can be typed in pretty quickly. For instance, we created an SXFM file for a feature model containing 287 features in about 10-15 minutes without a single mouse click.

The SXFM format also refrains from using tags for describing features thus keeping the size of typed XML files small.

<feature_model name="My feature model">     <-- feature model start tag and name attribute (mandatory)
  <meta>                                                                  <-- Optional
  <data name="description">Model description</data>                 <-- Optional
  <data name="creator">Model's creator</data>                       <-- Optional
  <data name="email">Model creator's email</data>                   <-- Optional
  <data name="date">Model creation date</data>                      <-- Optional
  <data name="department">Model creator's department</data>         <-- Optional
  <data name="organization">Model creator's organization</data>     <-- Optional
  <data name="address">Model creator's address</data>               <-- Optional
  <data name="phone">Model creator's phone</data>                   <-- Optional
  <data name="website">Model creator's website</data>               <-- Optional
  <data name="reference">Model's related publication</data>         <-- Optional
  </meta>
  <feature_tree>                <-- feature tree start tag
    :r root (root_id)                 <-- root feature named 'root' with unique ID 'root_id'   						
      :o opt1 (id_opt1)               <-- an optional feature named opt1 with unique id id_opt1
      :o opt2 (id_opt2)               <-- an optional feature named opt2, child of opt1 with unique id id_opt2
      :m man1                         <-- an mandatory feature named man1 with unique id id_man1
        :g [1,*]                      <-- an inclusive-OR feature group with cardinality [1..*] ([1..3] also allowed)
          : a (id_a)                  <-- a grouped feature name a with ID id_a
          : b (id_b)                  <-- a grouped feature name b with ID id_b
            :o opt3 (id_opt3)         <-- an optional feature opt3 child of b with unique id id_opt3
          : c (id_c)                  <-- a grouped feature name c with ID id_c
        :g [1,1]                      <-- an exclusive-OR feature group with cardinality [1..1]
          : d (id_d)                  <-- a grouped feature name d with ID id_d
          : e (id_e)                  <-- a grouped feature name e with ID id_e
            :g [2,3]                      <-- a feature group with cardinality [2..3] children of feature e
              : f (id_f)                  <-- a grouped feature name f with ID id_f
              : g (id_g)                  <-- a grouped feature name g with ID id_g
              : h (id_h)                  <-- a grouped feature name h with ID id_h
  </feature_tree>               <-- feature tree end tag (mandatory)
  <constraints>                 <-- extra constraints start tag (mandatory)
    c1: ~id_a or id_opt2        <-- extra constraint named c1: id_a implies id_opt2 (must be a CNF clause)
    c2: ~id_c or ~id_e          <-- extra constraint named c2: id_c excludes id_e (must be a CNF clause)
  </constraints>                <-- extra constraint end tag (mandatory)
</feature_model>                <-- feature model end tag  (mandatory)

Important:

• Tags <data> are optional but encouraged
• Feature tree must have at least one feature, i.e., the root node
• Extra constraints are optional
• Each extra constraint must be a CNF clause (any arity)
• Use feature IDs (as opposed to names) to write extra constraints
• Don not use parantheses to write extra constraints

The levels in the feature tree are distinguished by tabulations (\t). So the file exemplified above has hidden tabulations like this:

...
:r root (root_id)
\t:o opt1 (id_opt1)
\t:o opt2 (id_opt2)
\t:m man1        
\t\t:g [1,*]
\t\t\t: a (id_a)
\t\t\t: b (id_b)
\t\t\t\t:o opt3 (id_opt3)
\t\t\t: c (id_c)
...

Here you will find a Java parser library for reading SXFM files and a sample file to use the parser.