For each PDF/A-1 validation issue we try to explain what it means and, if possible how to resolve it. For a more technical explanation of the issue we quote the related section of the ISO 19005-1 PDF/A Specification.
The RDF Syntax Specification [7] mandates in section 6.1.4 “Attribute Event”:
"Several RDF attributes, including about, parseType, and a few others can be written without any namespace prefix. ... New documents SHOULD NOT use these unqualified attributes and applications MAY choose to warn when the unqualified form is seen in a document."
For example, the following construct is considered deprecated, and should not be used:
rdf:Description about=""
The following variant is preferred over the above since it avoids the deprecated use of an unqualified about attribute:
rdf:Description rdf:about="""
While Acrobat 8 accepts unqualified about attributes, the W3C Validator warns as follows:
Error: W102 unqualified use of rdf:about is deprecated.
Unqualified about attributes are occasionally used in examples in the XMP Specification [4], but should generally be avoided in XMP for PDF/A-1.