Data Warehouses and the Semantic Web - Data Warehouse Systems: Design and Implementation - page 531

http://example.org/NWDW#hasEmployee

http://example.org/NWDW#iri http://example.org/NWDW#employee1

http://example.org/NWDW#HireDate http://example.org/NWDW#LastName

http://example.org/NWDW#FirstName

1992-05-01 Nancy Davolio

Fig. 14.1 An example of an RDF graph

Figure 14.1 depicts an RDF graph representing an employee of the
Northwind company, her first name, last name, and hire date. The following
piece of RDF/XML code describes this graph.

< xml version '' 1.0 '' encoding= '' utf8 '' ? >
< rdf:RDF
xmlns:rdf= '' http://www.w3.org/1999/02/22-rdf-syntax-ns# ''
xmlns:ex= '' http://example.org/NWDW# '' >
< rdf:Description rdf:about= '' http://example.org/NWDW#iri '' >
< ex:hasEmployee >
< rdf:Description rdf:about= '' http://example.org/NWDW#employee1 '' >
< ex:FirstName > Nancy < /ex:FirstName >
< ex:LastName > Davolio < /ex:LastName >
< ex:HireDate > 1992-05-01 < /ex:HireDate >
< /rdf:Description >
< /ex:hasEmployee >
< /rdf:Description >
< /rdf:RDF >

The first line is the typical XML heading line, and the document starts
with the RDF element. The xmlns attribute is used to define XML namespaces
composed of a prefix and an IRI, making the text less verbose. The subject
and object of the triple representing the company and its employee are within
Description elements, where the attribute rdf:about indicates the IRIs of the
resources. The ex prefix refers to the Northwind data warehouse.
The same triple will be written as follows using Turtle:

@prefix rdf: < http://www.w3.org/1999/02/22-rdf-syntax-ns# > .
@prefix ex: < http://example.org/NWDW# > .

ex:iri ex:hasEmployee ex:employee1 .
ex:employee1 rdf:type ex:Employee ; ex:FirstName '' Nancy '' ;
ex:LastName '' Davolio '' ;ex:HireDate '' 1992-05-01 '' .

Note that Turtle provides a much simpler, less verbose syntax, compared to
RDF/XML, so we use Turtle in the remainder of the chapter.
Data types are supported in RDF through the XML data type system.
For example, by default ex:HireDate would be interpreted as a string value
rather than a date value. To explicitly define the data types for the example
above, we would write in Turtle: