[xacml] 0092: [Polar] PH09: New section 7.4.2 Attributes

[Anne Anderson <Anne.Anderson@Sun.com>]

---------Forwarded from Seth Proctor (with mods by Anne)--------
TEXT LOCATION: 7.4.2.1 Attribute Retrieval (new per #92)

TEXT CHANGE: Replace

    7.4.2.1 Attribute Retrieval

    The PDP SHALL retrieve the values of attributes that match
    the particular attribute designator or attribute selector and
    form them into a bag of values with the specified
    DataType. If no attributes from the request context match,
    the attribute shall be considered missing, and an empty bag
    is said to be retrieved.

 with:

    7.4.2.1 Attribute Retrieval

    The PDP SHALL retrieve the values of attributes that match
    the particular attribute designator or attribute selector and
    form them into a bag of values with the specified DataType.
    A bag containing one value is treated as semantically
    equivalent to a single value of the specified bag type.  If
    no attributes from the request context match, the attribute
    shall be considered missing, and an empty bag is said to be
    retrieved.

DISCUSSION:
    
Given the original text quoted above, an AD/AS will always return
a bag, which is always an error to most of the standard
functions, unless a bag with only one element is considered to be
the same as a single instance of just the element inside the
bag.  The text change clarifies this.