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In “RDFa in XHTML: Syntax and Processing,” Section 5.5, Step 4, the specifications say “if the element is the head or body element then act as if there is an empty @about present, and process it according to the rule for @about, above.” However, I can’t find any mention of how an “empty” about should be processed, nor exactly what constitutes an “empty” @about.

First, would an “empty @about consist of about=””?

Second, does it merely create an explicit bNode that has no author specified identifier? (Something that has sometimes been referred to as an “anonymous bNode” within the RDFa documentation.)

Paul Sweatte
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GrantRobertson
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1 Answers1

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A string with no characters is defined as an empty attribute value. The RDF Semantics spec defines the resulting node as follows:

Blank nodes are treated as simply indicating the existence of a thing, without using, or saying anything about, the name of that thing.

Some features are based on the existence of blank nodes:

  • automation relabelling, since the strings used to label blank-nodes (implicit positions) do not matter so long as they do not collide with other such labels

  • shortcuts for RDF lists

For example, an ordered list of Tennis Grand Slam names:

the Turtle shortcut:

:GrandSlam :order (:AustralianOpen :FrenchOpen
:Wimbledon :USOpen)

square-bracket syntax:

:GrandSlam :order
[ rdf:first :AustralianOpen ; rdf:rest
[ rdf:first :FrenchOpen ; rdf:rest
[ rdf:first :Wimbledon ; rdf:rest
[ rdf:first :USOpen ; rdf:rest rdf:nil ]]]]

the triple-form

GrandSlam :order _:b1 .
_:b1 rdf:first :AustralianOpen . _:b1 rdf:rest _:b2 .
_:b2 rdf:first :FrenchOpen . _:b2 rdf:rest _:b3 
_:b3 rdf:first :Wimbledon . _:b3 rdf:rest _:b4 .
_:b4 rdf:first :USOpen . _:b4 rdf:rest rdf:nil

References

Paul Sweatte
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