subjectScheme and extension

Here is the normative content from the DITA 1.2 spec
    (Language Reference):

      

      3.1.5.1.2 schemeref

    A <schemeref> element provides a reference to another scheme.
    Typically, the referenced scheme defines a base set of controlled
    values extended by the current scheme. The values in the referenced
    scheme are merged with the current scheme; the result is equivalent
    to specifying all of the values in a single map.

    

    All the specific content about extending the subjectScheme (whether
    upwards or downwards) then is laid out in the examples.

    

    Here is the normative ontent from the draft DITA 1.3 spec (Architectural
    Specification and Language Reference):

    

    2.2.3.5 Extending subject schemes

    The <schemeref> element provides a mechanism for extending a
    subject scheme. This makes it possible to add new relationships to
    existing subjects and extend enumerations of controlled values.

    

    The <schemeref> element provides a reference to another
    subject scheme map. Typically, the referenced subject-scheme map
    defines a base set of controlled values that are extended by the
    current subject-scheme map. The values in the referenced
    subject-scheme map are merged with the values in the current
    subjectscheme map; the result is equivalent to specifying all of the
    values in a single subject scheme map.

    

    3.6.1.2 <schemeref>

    A <schemeref> element references another subject scheme map.
    Typically, the referenced subject scheme defines a base set of
    controlled values; the referencing map then extends the base set of
    controlled values. The values specified in the subject scheme maps
    are merged; the result is equivalent to specifying all of the values
    in a single map.

    

    My inclination is to leave this as-is.

    

    
-- 

      Best,

      Kris

      

      Kristen James Eberlein

      Chair, OASIS DITA Technical Committee

      Principal consultant, Eberlein Consulting

      www.eberleinconsulting.com

      +1 919 682-2290; kriseberlein (skype)