Question

So here is an entry in rdf format. I’d like to understand why some parts of it seem so convoluted.

<pgterms:file rdf:about="&f;dirs/3/1/9/0/31900/31900-8.zip">
  <dc:format><dcterms:IMT><rdf:value>text/plain; charset="iso-8859-1"</rdf:value></dcterms:IMT></dc:format>
  <dc:format><dcterms:IMT><rdf:value>application/zip</rdf:value></dcterms:IMT></dc:format>
  <dcterms:extent>193120</dcterms:extent>
  <dcterms:modified><dcterms:W3CDTF><rdf:value>2010-04-06</rdf:value></dcterms:W3CDTF></dcterms:modified>
  <dcterms:isFormatOf rdf:resource="#etext31900" />
</pgterms:file>

In particular, this value:

<dc:format><dcterms:IMT><rdf:value>text/plain; charset="iso-8859-1"</rdf:value></dcterms:IMT></dc:format>

Why does it need both a dcterms:IMT AND an rdf:value portion? This just seems like a lot of bloat for what appears to be little practical benefit. Since it is already using MIME types, it just doesn’t make sense to me.

Answer 1

Why does xml have so many angle brackets my eyes hurt….because it was meant to be read by a parser not by humans.

Your sample is not rdf (rdf is the framework), it is rdf/xml, one possible serialzation of a graph in the framework. Turtle/n3 is much prettier serialization. N-Triples is super simple.

Some very small examples that don’t cover any real details but…

RDF/XML:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/">
  <rdf:Description rdf:about="http://www.w3.org/2001/sw/RDFCore/ntriples/">
    <dc:creator>Art Barstow</dc:creator>
    <dc:creator>Dave Beckett</dc:creator>
    <dc:publisher rdf:resource="http://www.w3.org/"/>
  </rdf:Description>
</rdf:RDF>

N-Triples

<http://www.w3.org/2001/sw/RDFCore/ntriples/> <http://purl.org/dc/elements/1.1/creator> "Dave Beckett" .
<http://www.w3.org/2001/sw/RDFCore/ntriples/> <http://purl.org/dc/elements/1.1/creator> "Art Barstow" .
<http://www.w3.org/2001/sw/RDFCore/ntriples/> <http://purl.org/dc/elements/1.1/publisher> <http://www.w3.org/> .

N3

@prefix dc: <http://purl.org/dc/elements/1.1/>

<http://www.w3.org/2001/sw/RDFCore/ntriples/> 
     dc:creator "Dave Beckett";
     dc:creator "Art Barstow";
     dc:publisher <http://www.w3.org/>.

EDIT: you can stop reading, this is just the example provided by OP in different serialization. To answer to the question

Why does it need both a dcterms:IMT AND an rdf:value portion?

rdf/xml has to do kind of a stutter-step when there are “Blank Nodes”. you can see below that N-Triples writes the blank nodes out and n3 attempts to make it more obvious what the relations are.
All of these are serialzations of the same rdf graph.

RDF/XML slightly modified (namespace added) so it parses:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:dcterms="http://purl.org/dc/terms/"
         xmlns:pgterms="http://www.gutenberg.org/rdfterms/">
<pgterms:file rdf:about="/home/me/dirs/3/1/9/0/31900/31900-8.zip">
  <dc:format><dcterms:IMT><rdf:value>text/plain; charset="iso-8859-1"</rdf:value></dcterms:IMT></dc:format>
  <dc:format><dcterms:IMT><rdf:value>application/zip</rdf:value></dcterms:IMT></dc:format>
  <dcterms:extent>193120</dcterms:extent>
  <dcterms:modified><dcterms:W3CDTF><rdf:value>2010-04-06</rdf:value></dcterms:W3CDTF></dcterms:modified>
  <dcterms:isFormatOf rdf:resource="#etext31900" />
</pgterms:file>
</rdf:RDF>

N-Triples

</home/me/dirs/3/1/9/0/31900/31900-8.zip> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.gutenberg.org/rdfterms/file> .
</home/me/dirs/3/1/9/0/31900/31900-8.zip> <http://purl.org/dc/elements/1.1/format> _:LqSOByLi19 .
</home/me/dirs/3/1/9/0/31900/31900-8.zip> <http://purl.org/dc/elements/1.1/format> _:LqSOByLi20 .
</home/me/dirs/3/1/9/0/31900/31900-8.zip> <http://purl.org/dc/terms/isFormatOf> <#etext31900> .
</home/me/dirs/3/1/9/0/31900/31900-8.zip> <http://purl.org/dc/terms/modified> _:LqSOByLi21 .
</home/me/dirs/3/1/9/0/31900/31900-8.zip> <http://purl.org/dc/terms/extent> "193120" .
_:LqSOByLi21 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://purl.org/dc/terms/W3CDTF> .
_:LqSOByLi21 <http://www.w3.org/1999/02/22-rdf-syntax-ns#value> "2010-04-06" .
_:LqSOByLi20 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://purl.org/dc/terms/IMT> .
_:LqSOByLi20 <http://www.w3.org/1999/02/22-rdf-syntax-ns#value> "application/zip" .
_:LqSOByLi19 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://purl.org/dc/terms/IMT> .
_:LqSOByLi19 <http://www.w3.org/1999/02/22-rdf-syntax-ns#value> "text/plain; charset=\"iso-8859-1\"" .

N3/Turtle

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
@prefix dcterms: <http://purl.org/dc/terms/> .
@prefix pgterms: <http://www.gutenberg.org/rdfterms/> .

</home/me/dirs/3/1/9/0/31900/31900-8.zip> a pg:file;
    dc:format 
        [ a dcterms:IMT;  rdf:value "text/plain; charset=\"iso-8859-1\"" ],
        [ a dcterms:IMT;  rdf:value "application/zip" ];
    dcterms:extent "193120";
    dcterms:isFormatOf <#etext31900>;
    dcterms:modified [ a dcterms:W3CDTF; rdf:value "2010-04-06" ] .

Note: N3 is even prettier if it’s colored

EDIT 2:
The above describes that there is a bnode but as to why there is one….the dcterms:modified predicate in the last line of the N3 serialization above could (I wish) be viewed more like:

dcterms:modified "2010-04-06"^^dcterms:W3CDTF
# vs
dcterms:modified [ a dcterms:W3CDTF; rdf:value "2010-04-06" ]

The reason that rdf:value even exists is for triples like:

exproduct:item10245   exterms:weight   [rdf:value        "2.4"^^xsd:decimal
                                        exterms:units    exunits:kilograms] .

In addition to units the node could indicate precision or other characteristics of the object of the triple.

Yeah I kind of hate the rdf:value thing as damaging to understanding and practicality in favor of epistemological purity.