1. Transport and Access of Data, Metadata, and Semantics using RDF
M.Benno Blumenthal International Research Institute for Climate and Society Columbia University

2. RDF: framework for writing connections
Subject
Predicate (a.k.a. property)
Object
{SST a cfatt:non_coordinate_variable,
SST cfatt:standard_name cf:sea_surface_temperature,
SST netcdf:hasDimension longitude }
URI’s identify everything
RDF/OWL has mostly been touted for controlled vocabularies like cf:sea_surface_temperature. And it is important for that – we put, rightly or wrongly, a lot of semantics in the variable names.

3. OWL: writing ontologies
Standard properties for relating (in RDF)
Classes
data-type properties
object-type properties
Can describe both data and metadata conventions in the same framework (RDF)
Machine-readable convention statement
Can interrelate metadata conventions
Lets us explicate the implicit in our codes

4. RDF/OWL lets us address a number of current issues
Imprecise semantics
Implicit semantics/relationships
Convention-conforming or bust
Code Isolation
Local Semantics

5. Imprecise Semantics
Attributes not necessarily attached to a convection are machine-interpretable if there is one all-encompassing convention that give them meaning
Conventions attribute with multiple values works as long as no two conventions use the same name, but requires parser to know the conventions so that attributes can be properly assigned

6. Implicit Semantics
Netcdf – same name implies same meaning becomes a translation problem when converted to a scheme that explicitly represents such connections.
Implicit means you don’t know for sure that the author intended the implication, e.g. string dimensions

7. Convention or Bust
Schemes with fully-determined metadata cannot transport anything less, e.g. WCS, GRIB, …
Clients that insist on a particular convention have the same problem even with a general transport mechanism. This problem can be hidden inside a library, e.g. java opendap.

8. Code Isolation
Changes in metadata force data transport schema changes

9. Local Semantics
Even without mapping to standard metadata, we need to express the relationships between variables in a dataset
Example: additional non-standard information (like statistical moments) about variables that have standard metadata
Particularly important with evolving standards, merging fields of study

10. OpenDAP, DAP4, and RDF