*TODO*

## Readability

## XMP, RDFa and RDF

RDF is an abstract data model for knowledge graphs,
usable for domain-specific annotations:
Terminology for a domain is established by referencing a shared ontology,
and terms are composed as sets of subject-predicate-object triples.
RDF includes one language, Turtle, strives to be human readable,
and languages for embedding triples into other data structures,
notably XMP for PDF files and RDFa for HTML.

RDF is an abstract data model for knowledge graphs.
Multiple RDF languages exist,
each covering all or subsets of the RDF model,
including human readability optimized Turtle,
RDFa for HTML embedding
and XMP for PDF embedding.
Each RDF language have different constraints,
e.g. the XMP language for storing RDF in media files
can express express one RDF graph in each XMP object
[@Adobe2012, p. 9].

*TODO*
