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---+ Creating a Windows Forms Application To Access RDF Data Using The Virtuoso ADO.Net Provider
%TOC%
---++ Introduction
This document will guide you through creating a simple application that allows you to access RDF
data in a Virtuoso database as an Entity <nowiki>DataSet</nowiki> and explore that RDF data in
an intuitive way by clicking on dereferenceable
[[http://docs.openlinksw.com/virtuoso/rdfdatarepresentation.html#rdfiriidtype][IRIs]].
---++ Prerequisites
1 Microsoft Visual Studio 2008
1 The Virtuoso ADO.Net provider for .Net 3.5 and the Entity Framework
1 The example assumes that you have a local Virtuoso server with the Northwind demo
database installed. If the demo database is not already installed then download the
[[http://s3.amazonaws.com/opldownload/uda/vad-packages/6.1/virtuoso/demo_dav.vad][demo database VAD package]]
(<code>demo_dav.vad</code>) and install it. The VAD package will create a new database in
Virtuoso called demo containing the familiar Northwind tables. It will also creates
[[http://docs.openlinksw.com/virtuoso/rdfsparqlintegrationmiddleware.html#rdfviews][Linked Data Views]]
of the Northwind tables. In the example we assume the database is accessible on a hostname of
"<code>demo.openlinksw.com</code>" on the default port <code>80</code>, where an actually live
instance of the Virtuoso Demo database is hosted. Users would use the appropriate hostname and
port number of their Virtuoso installation to create the sample application, and would be
<code>localhost:8890</code> for a default installation or whatever the
<code>[[http://docs.openlinksw.com/virtuoso/databaseadmsrv.html#ini_URIQA][URIQA DefaultHost]]</code>
Virtuoso configuration parameter is set to when the demo database VAD package is installed.
---++ Creating the Application
---+++ Step 1 - Create a view of the RDF data
We want to be able to access the RDF data in Visual Studio and the easiest way to do this is
to create a view of the data that we are interested in and bind that view to a
<nowiki>DataSet</nowiki>. This can be considered as using server side
[[http://docs.openlinksw.com/virtuoso/rdfsparql.html][SPARQL]]. Virtuoso supports an
extension to standard SQL that allows execution of
[[http://docs.openlinksw.com/virtuoso/rdfsparql.html#rdfsparqlinline][SPARQL within a SQL statement]].
If a SQL query begins with the keyword SPARQL then the rest of the query is interpreted by
as SPARQL. If a SPARQL query is used as the definition of a view then that view can be
manipulated using SQL like any other view. In this way the result set from a SPARQL query
can be easily accessed from Visual Studio using ADO.Net and the Entity Framework.
1. To create a view of the customers in the Northwind, first open the Virtuoso Conductor and log
in as dba.
* <b>Note:</b>
* If the view is added to the Visual Studio project as user "demo" (or any other than "dba'),
then it must be ensured that the "SPARQL_SELECT" and "SPARQL_SPONGE" roles are assigned to this
user, which can be done via the Virtuoso Conductor in the "System Admin" -> "User Accounts" tab.
* Execute permissions will also need to be granted to the following procedure:
<verbatim>
GRANT EXECUTE
ON DB.DBA.RDF_MAKE_LONG_OF_SQLVAL
TO "demo"
</verbatim>
1. Then open <nowiki>iSQL</nowiki> from the menu on the left and execute the following
statement --
<verbatim>
CREATE VIEW Demo.demo.sparqlview AS
SPARQL
PREFIX nwind: <http://demo.openlinksw.com/schemas/northwind#>
SELECT DISTINCT ?s
FROM <http://demo.openlinksw.com/Northwind>
WHERE { ?s a nwind:Customer }
</verbatim>
%BR%%BR%<img src="%ATTACHURLPATH%/CreateView.png" style="wikiautogen"/>%BR%%BR%
---+++ Step 2 - Create a simple grid form in Visual Studio
1 Open *Visual Studio* and create a new *Windows Forms Application* called
<nowiki>RDFDemo</nowiki>.
1 In the *Form Designer* drag a <b><nowiki>DataGridView</nowiki></b> on to the form.
1 Click the *Choose Data Source* drop down and select *Add Project Data Source*.
%BR%%BR%<img src="%ATTACHURLPATH%/AddDataSource.png" style="wikiautogen"/>%BR%%BR%
1 In the *Data* *Source* *Configuration Wizard* choose *Database* and then set up
a connection to the demo database on your local Virtuoso server.
1 On the *Choose Your Data Objects* page expand the *Views* and select sparqlview.
%BR%%BR%<img src="%ATTACHURLPATH%/ChooseDataSourceObject.png" style="wikiautogen"/>%BR%%BR%
1 Click *Finish*.
1 In the *Form* *Designer* select <nowiki>dataGridView1</nowiki> and change the
<b><nowiki>AutoSizeColumnsMode</nowiki></b> to <nowiki>AllCellsExceptHeader</nowiki>.
1 Select the <b><nowiki>DefaultCellStyle</nowiki></b> and click on the ellipsis. This will
open the <b><nowiki>CellStyleBuilder</nowiki></b>. Change the <b><nowiki>ForeColor</nowiki></b>
to Blue.
%BR%%BR%<img src="%ATTACHURLPATH%/CellStyleBuilder.png" style="wikiautogen"/>%BR%%BR%
1 Expand *Font* and change *Underline* to True. Click *OK*.
---+++ Step 3 - Change the mapping of the <nowiki>DataSet</nowiki>
1 In the *Solution Explorer* you will now have a <b><nowiki>DataSet</nowiki></b> called
<nowiki>DemoDataSet.xsd</nowiki>.
1 If you double click on this it opens the <b><nowiki>DataSet</nowiki> Designer</b>.
1 Select the column called s in the sparqlview table, and in the *Properties* pane,
change the <b><nowiki>DataType</nowiki></b> from System.String to System.Object.
* The data returned by a SPARQL query can either be an
[[http://docs.openlinksw.com/virtuoso/rdfdatarepresentation.html#rdfiriidtype][IRI]]
or a literal value. In order to distinguish between the two the Virtuoso ADO.Net
provider defines an additional data type, <nowiki>SQLExtendedString</nowiki>. By setting
the column type to System.Object we can cast the fetched data back to
<nowiki>SQLExtendedString</nowiki> and find out if an individual value is an
IRI or a literal and handle it appropriately.
---+++ Step 4 - Create the on_click event handler for the cells in the <nowiki>DataGridView</nowiki>
1 Return to the *Form* *Designer* and double click on the cell of the
<b><nowiki>DataGridView</nowiki></b>. This creates the
<b><nowiki>dataGridView1_CellContentClick</nowiki></b> method in Form1.cs.
This is the method that handles clicking on
IRI objects in the grid.
1 Paste the following block of code into the body of the
<b><nowiki>dataGridView1_CellContentClick</nowiki></b> method.
<verbatim>
int column = e.ColumnIndex;
object o = dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value;
Type t = dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].ValueType;
if (o is SqlExtendedString)
{
SqlExtendedString se = (SqlExtendedString) o;
ExtendedStringHandler seHandler = new ExtendedStringHandler(se, this.sparqlviewTableAdapter.Connection);
seHandler.displayData();
}
else if (o is SqlRdfBox)
{
//doesn't do anything at the moment
}
</verbatim>
1 As we are using the <nowiki>SQLExtendedString</nowiki> extension from the Virtuoso ADO.Net
provider you will also need to add
<verbatim>
using OpenLink.Data.Virtuoso;
</verbatim>
at the top of the file.
---+++ Step 5 - Create a class to handle exploring the RDF data
1 Add a new C# class to the project called <nowiki>ExtendedStringHandler</nowiki>, by
right-clicking on RDFDemo in the *Solution* *Explorer* and *Add* a <b><nowiki>Class</nowiki></b>.
1 Add the following using statements to the top of the file
<verbatim>
using OpenLink.Data.Virtuoso;
using System.Data;
using System.Windows.Forms;
using System.Drawing;
using System.Data.Mapping;
using System.Data.Common;
</verbatim>
1 Paste the following block of code into the class definition.
<verbatim>
StringBuilder DescribeCommand;
VirtuosoConnection ParentConnection;
List<Label> labelList = new List<Label>();
List<TextBox> textBoxList = new List<TextBox>();
DescribeDataSet describeDataSet = new DescribeDataSet();
Boolean isIRI = false;
public ExtendedStringHandler(SqlExtendedString iri, VirtuosoConnection parentConnetion)
{
ParentConnection = parentConnetion;
if (iri.IriType == SqlExtendedStringType.IRI)
{
isIRI = true;
DescribeCommand = new StringBuilder("sparql SELECT * FROM <http://demo.openlinksw.com/Northwind> WHERE {<" + iri.ToString() + "> ?p ?o}");
// Replace demo.openlinksw.com in line above with your URIQA DefaultHost setting
}
}
public string describeCommandText
{
get
{
return DescribeCommand.ToString();
}
}
public void getDescribeData()
{
VirtuosoCommand myCommand = new VirtuosoCommand(this.describeCommandText, this.ParentConnection);
VirtuosoDataAdapter myAdapter = new VirtuosoDataAdapter();
myAdapter.SelectCommand = myCommand;
myAdapter.Fill(describeDataSet.DataTable1);
}
public void displayData()
{
if (isIRI)
{
getDescribeData();
Form describeForm = new Form();
describeForm.AutoScroll = true;
describeForm.Width = 840;
Label label1 = new Label();
label1.AutoSize = true;
label1.Font = new Font(label1.Font.FontFamily, label1.Font.Size + 3.0F, label1.Font.Style | FontStyle.Bold, label1.Font.Unit);
describeForm.Controls.Add(label1);
DataTable table1 = describeDataSet.Tables[0];
if (table1.Rows.Count == 0)
label1.Text = "No Details Available";
else
{
foreach (DataRow row in table1.Rows)
if (row[0].ToString() == "http://www.w3.org/1999/02/22-rdf-syntax-ns#type")
{
StringBuilder title = new StringBuilder(row[1].ToString() + " details");
label1.Text = title.ToString();
break;
}
foreach (DataRow row in table1.Rows)
{
Label propertyLabel = new Label();
TextBox valueBox = new TextBox();
valueBox.Width = 400;
object property = row[0];
object value = row[1];
if (value is SqlExtendedString)
{
valueBox.ForeColor = Color.Blue;
valueBox.Font = new Font(valueBox.Font.FontFamily, valueBox.Font.Size, valueBox.Font.Style | FontStyle.Underline, valueBox.Font.Unit);
}
propertyLabel.Text = row[0].ToString();
propertyLabel.AutoEllipsis = true;
propertyLabel.AutoSize = false;
propertyLabel.Width = propertyLabel.PreferredWidth > 380 ? 380 : propertyLabel.PreferredWidth;
Binding bind = new Binding("Text", row[1], "");
valueBox.DataBindings.Add(bind);
labelList.Add(propertyLabel);
textBoxList.Add(valueBox);
}
for (int i = 0; i < table1.Rows.Count; i++)
{
textBoxList[i].Click += new EventHandler(this.iri_Click);
labelList[i].Location = new Point(10, i * 20 + 50);
textBoxList[i].Location = new Point(400, i * 20 + 50);
describeForm.Controls.Add(labelList[i]);
describeForm.Controls.Add(textBoxList[i]);
}
describeForm.Height = labelList.Count * 20 + 100 > 500 ? 500 : labelList.Count * 20 + 100;
}
describeForm.ShowDialog();
}
else
{
Form blankForm = new Form();
Label label1 = new Label();
label1.Text = "Blank Node";
label1.Font = new Font(label1.Font.FontFamily, label1.Font.Size + 3.0F, label1.Font.Style | FontStyle.Bold, label1.Font.Unit);
blankForm.ShowDialog();
}
}
public void iri_Click(object sender, EventArgs e)
{
int boxNum = 0;
for (int i = 0; i < textBoxList.Count; i++)
{
if (sender == textBoxList[i])
{
boxNum = i;
break;
}
}
Object o = describeDataSet.DataTable1.Rows[boxNum][1];
if (o is SqlExtendedString)
{
SqlExtendedString se = (SqlExtendedString)o;
ExtendedStringHandler seHandler = new ExtendedStringHandler(se, ParentConnection);
seHandler.displayData();
}
else if (o is SqlRdfBox)
{
//doesn't do anything at the moment
}
}
</verbatim>
1 The <nowiki>ExtendedStringHandler</nowiki> class creates a new SPARQL query based on the IRI
that was clicked. This query is executed against Virtuoso using the ADO.Net connection in
the same way that any SQL statement would be executed across an ADO.Net connection. This
can be considered as Client Side SPARQL. The result set from the query describes the selected
object and is returned as an ADO.Net <nowiki>DataAdapter</nowiki>. The
<nowiki>DataAdapter</nowiki> is used to fill a <nowiki>DataTable</nowiki> which is displayed
on a new form. We now need to add the new <nowiki>DataSet</nowiki> to the project and define
the <nowiki>DataTable</nowiki> that will hold the query results.
---+++ Step 6 - Add a new Data Set to hold the query results
1 Right click RDFDemo in the *Solution* *Explorer* and add a new
<b><nowiki>DataSet</nowiki></b>. Call the new <b><nowiki>DataSet</nowiki></b>
<nowiki>DescribeDataSet</nowiki>.
%BR%%BR%<img src="%ATTACHURLPATH%/NewDataSet.png" style="wikiautogen"/>%BR%%BR%
1 Double click on <nowiki>DescribeDataSet</nowiki> in the *Solution Explorer* to open
the <b><nowiki>DataSet</nowiki> Designer</b> and drag a <b><nowiki>DataTable</nowiki></b>
from the <b>Toolbox</b> into it.
1 Add two columns, p and o, to the <b><nowiki>DataTable</nowiki></b> and set the
<b><nowiki>DataType</nowiki></b> of each column to System.Object.
%BR%%BR%<img src="%ATTACHURLPATH%/NewDataTable.png" style="wikiautogen"/>%BR%%BR%
---+++ Step 7 - Build and run the application
1 You should see a form displaying all the Northwind customers, like this.
%BR%%BR%<img src="%ATTACHURLPATH%/Form1.png" style="wikiautogen"/>%BR%%BR%
1 When any customer is clicked it opens a new form showing customer details.
%BR%%BR%<img src="%ATTACHURLPATH%/CustomerDetails.png" style="wikiautogen"/>%BR%%BR%
1 Clicking on the links in the new form allows you to drill down further to get order,
product, location details etc.
%BR%%BR%<img src="%ATTACHURLPATH%/OrderDetails.png" style="wikiautogen"/>%BR%%BR%
%BR%%BR%<img src="%ATTACHURLPATH%/OrderLineDetails.png" style="wikiautogen"/>%BR%%BR%
---++ Next Steps
You will notice if you keep clicking on the links that this application will only display
data that is held in the Northwind graph. Clicking on an external link, for example the
link to Berlin in dbpedia, <nowiki>http://dbpedia.org/resource/Berlin</nowiki>, results
in a empty window and an error message. The next step is to
[[VirtSPASQLRDFDemoExternalDereferencing][extend this application so that it can handle dereferencing external IRIs]].
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