M.Benno Blumenthal and John del Corral International Research Institute for Climate and Society OpenDAP Using Resource Description Framework (RDF) to carry metadata for datasets

RDF is important for OpenDAP because By embedding OpenDAP in an RDF document, metadata (a.k.a. attributes) not understood by OpenDAP code are easily carried in a semantically-valid way Explicit relationships between OpenDAP variables can cleanly solve netcdf common name vs OpenDAP GRID/MAP structures, while avoiding retransmission of common independent variables Explicit mapping between the different data models of the different OpenDAP APIs

RDF is important for OpenDAP because Support for different languages can be built on top of RDF object support, e.g. Ruby ActiveRDF

Why RDF? Web-based system for interoperating semantics A key part of the Semantic Web RDF/OWL is an interesting technology, but it is even more interesting when it is clear that it can help solve our problems

Standard Metadata Users Datasets Tools Standard Metadata Schema/Data Services

Many Data Communities Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema

Super Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Standard metadata schema

Super Schema: direct Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Standard metadata schema/data service

Flaws A lot of work Super Schema/Service is the Lowest- Common-Denominator Science keeps evolving, so that standards either fall behind or constantly change

RDF Standard Data Model Exchange Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Tools Users Datasets Standard Metadata Schema Standard metadata schema RDF

Standard metadata schema Tools Users Datasets Standard Metadata Schema RDF Tools Users Datasets Standard Metadata Schema RDF Tools Users Datasets Standard Metadata Schem RDF RDF Data Model Exchange RDF Tools Users Datasets Standard Metadata Schema RDF Tools Users Datasets Standard Metadata Schema RDF

RDF Architecture RDF Virtual (derived) RDF queries

Why is this better? Maps the original dataset metadata into a standard format that can be transported and manipulated Still the same impedance mismatch when mapped to the least-common-denominator standard metadata, but When a better standard comes along, the original complete-but-nonstandard metadata is already there to be remapped, and “late semantic binding” means everyone can use the new semantic mapping Can uses enhanced mappings between models that have common concepts beyond the least-common- denominator EASIER – tools to enhance the mapping process, mappings build on other mappings

CF attributes SWEET Ontologies Search Terms CF Standard Names IRIDL Terms NC basic attributes IRIDL attributes SWEET as Terms CF Standard Names As Terms Gazetteer Terms

Sample Tool: Faceted Search

Distinctive Features of the search Search terms are interrelated terms that describe the set of returns are displayed (spanning and not) Returned items also have structure (sub- items and superseded items are not shown)

Architectural Features of the search Multiple search structures possible Multiple languages possible Search structure is kept in the database, not in the code

Triplets of Subject Property (or Predicate) Object URI’s identify things, i.e. most of the above Namespaces are used as a convenient shorthand for the URI’s RDF: framework for writing connections

Datatype Properties {WOA} dc:title “NOAA NODC WOA01” {WOA} dc:description “NOAA NODC WOA01: World Ocean Atlas 2001, an atlas of objectively analyzed fields of major ocean parameters at monthly, seasonal, and annual time scales. Resolution: 1x1; Longitude: global; Latitude: global; Depth: [0 m,5500 m]; Time: [Jan,Dec]; monthly”

Object Properties {WOA} iridl:isContainerOf {Grid-1x1}, {Grid-1x1} iridl:isContainerOf {Monthly}

WOA01 diagram

Standard Properties {WOA} dcterm:hasPart {Grid-1x1}, {Grid-1x1} dcterm:hasPart {MONTHLY} Alternatively {WOA} iridl:isContainerOf {Grid-1x1}, {iridl:isContainerOf} rdfs:subPropertyOf {dcterm:hasPart}

{SST} rdf:type {cfatt:non_coordinate_variable}, {SST} cfatt:standard_name {cf:sea_surface_temperature}, {SST} netcdf:hasDimension {longitude} netcdf/CF in RDF Object properties provide a framework for explicitly writing down relationships between data objects/components, e.g. vague meaning of nesting is made explicit Properties also can be related, since they are objects too

RDF Tools Transport/Exchange (RDF/XML) Storage RDF APIs (Redland,Jena,Sesame) Query (SPARQL,SeRQL, …) Basic Semantics

Search Interface Term pdfhttp://iri.columbia.edu/~benno/sampleterm. pdf

Ontologies Use Conventions to connect concepts to established sets of concepts Generate additional “virtual” triples from the original set and semantics RDFS – some property/class semantics OWL – additional property/class semantics: more sophisticated (ontological) relationships

OWL Language for expressing ontologies, i.e. the semantics are very important. However, even without a reasoner to generate the implied RDF statements, OWL classes and properties represent a sophistication of the RDF Schema However, there is a serious split in world view from what we have been talking about: concepts as classes vs concepts as individuals

Faceted Search Explicated

Search Interface Items (datasets/maps) Terms Facets Taxa

Search Interface Semantic API {item} dc:title dc:description rss:link iridl:icon dcterm:isPartOf {item2} dcterm:isReplacedBy {item2} {item} trm:isDescribedBy {term} {term} a {facet} of {taxa} of {trm:Term}, {facet} a {trm:Facet}, {taxa} a {trm:Taxa}, {term} trm:directlyImplies {term2}

Faceted Search w/Queries

RDF Architecture RDF Virtual (derived) RDF queries

Data Servers Ontologies MMI JPL Standards Organizations Start Point RDF Crawler RDFS Semantics Owl Semantics SWRL Rules SeRQL CONSTRUCT Search Queries Location Canonicalizer Time Canonicalizer Sesame Search Interface bibliography IRI RDF Architecture

CF attributes SWEET Ontologies Search Terms CF Standard Names IRIDL Terms NC basic attributes IRIDL attributes SWEET as Terms CF Standard Names As Terms Gazetteer Terms

RDF is important for OpenDAP because By embedding OpenDAP in an RDF document, metadata (a.k.a. attributes) not understood by OpenDAP code are easily carried in a semantically-valid way Explicit relationships between OpenDAP variables can cleanly solve netcdf common name vs OpenDAP GRID/MAP structures, while avoiding retransmission of common independent variables Explicit mapping between the different data models of the different OpenDAP APIs Build on language support of RDF objects

Embedded OpenDAP Ontology

Topics/Issues OpenDAP and RDF: can we transport data semantics without fixing the entire schema?OpenDAP and RDF netcdf/HDF and RDF: do we need non- contextual modeling in our metadata transport/storage? Concepts as classes vs concepts as individuals Sub-classes vs sub-categories