Database Reference
In-Depth Information
Fig. 1.
Mashup Editor
3
Data Mashups Using XQuery
Figure 1 shows the interface of our system. The main window is divided into three
panels, namely data source selection, mashup editor, and query results.
Data Source Selection.
All available/registered data services are shown in the left panel
of Figure 1. Each data service describes its available data source, its functionality and
schema (if provided) which help the user to select the most suitable data service. Data
services can be arranged in different categories based on metadata provided while regis-
tering a data source. Alternatively, data services can be grouped according to their data
format (i.e., XML or RDF) by choosing the “data type” option in the left panel.
Mashup Editor.
The central panel in Figure 1 is the mashup editor. The user can select
any data service from the left panel and can easily drag and drop it into the mashup
editor. These data services can be combined via several data operations, which are also
selected by drag and drop from the left panel. The mashup is implemented by generating
an extended XQuery expression with sub-queries in SPARQL or XQuery following the
syntax in [3]. Figure 2 shows a sample extended XQuery expression generated by the
mashup editor after integrating XML and RDF data sources. This query contains a
SPARQL query as a sub-query inside XQuery. The mashup editor has both a design
view (by choosing the “mashup editor” option in the central panel) and a command line
interface (via the “source” option in the central panel). The design view provides an
easy graphical interface while the command line interface is used by an expert user to
write queries in the extended XQuery syntax described in [3]. For the creation of the
queries from the graphical interface we use a similar approach as described in [7] for
XQuery generation and [8] for SPARQL query generation.
Query Results.
In the right panel of Figure 1, the result of executing the query from the
mashup editor is displayed. The data format of the result is always XML. The user can
