IBM-DM-016: Problems with attribute node, typed-value accessor

Data Model Section 6.3.2 (Attribute Nodes--Accessors): The dm:typed-value 
accessor claims to return the "atomic value that is determined from its 
tuple representation." But (as in the case of element nodes), the 
properties of an attribute node do not include any such "tuple 
representation". The typed-value accessor should be defined in terms of 
the properties of the node, and these properties should be extended if 
necessary to support the accessor.