Filtering the XML Nodes bound with dropdownlist

[sachtech]

Hello Friends, I have two DropDownList: 1) CollegeDDL which contains Four static names of the colleges. : Homeopathic Medical College,Physiotherapy College,Institute of Ayurveda,Institute of Business Administration


2) CourseDDL which is bind to CourseDetail.XML.

 
        <Institutes>  
        <Institute>
        <InstituteName>  Homoeopathic Medical College  </InstituteName>
        <Course> <CourseName>  BHMS                    </CourseName> </Course>    
        <Course> <CourseName>  MD(Repertary)           </CourseName> </Course>    
        <Course> <CourseName>  MD(Organon of Medicine) </CourseName> </Course>    
        <Course> <CourseName>  MD(Materia Medica)      </CourseName> </Course>    
        </Institute>
 
        <Institute>
        <InstituteName>  Physiotherapy College  </InstituteName>
        <Course> <CourseName>  BPT          </CourseName> </Course>    
        <Course> <CourseName>  BPT(Sports)  </CourseName> </Course>    
        <Course> <CourseName>  BPT(Cardio)  </CourseName> </Course>
        </Institute>
 
        <Institute>
        <InstituteName>  Institute of Ayurved  </InstituteName>
        <Course> <CourseName>  BAMS          </CourseName> </Course>
        <Course> <CourseName>  BAMS(Nature)  </CourseName> </Course>
        <Course> <CourseName>  BAMS(Plants)  </CourseName> </Course>
        </Institute>
 
        <Institute>
        <InstituteName> Institute of Business Administration </InstituteName>
        <Course> <CourseName>BBA</CourseName> </Course>    
        <Course> <CourseName>DBM</CourseName> </Course>    
        <Course> <CourseName>BBA(Distance)</CourseName> </Course>    
        </Institute>
 

---------------------------------
CourseDetail.XSL

 
        <xsl:template match ="/">
 
        <Institute>
        <xsl:apply-templates select ="Institutes/Institute/Course"/>
        </Institute>
 
        </xsl:template>
 
 
        <xsl:template match ="Institutes/Institute/Course">
        <Institute>
        <xsl:attribute name="CourseName">
        <xsl:value-of select="CourseName"/>
        </xsl:attribute>
        </Institute>
 
        </xsl:template>
 
        </xsl:stylesheet> 

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I have bind Coursedetail.XML to CourseDDL and CourseDetail.XSL (No XPATH Expression)

After doing this, My CourseDDL is correctly filled with all the CourseName value of my XML file.
But now I want to filter the data bound to CourseDDL , based on College Name selected in CollegeDDL.

For Example:Currently my CourseDDL contains all the CourseName : BHMS,MD(Repertary),MD(Organon of Medicine),......,DBM,BBA(Distance).

But when I select "Homoeopathic Medical College" in CollegeDDL , The data bound to CourseDDL should filter accordingly.
It means when I select "Homoeopathic Medical College" , my CourseDDL should Display only that course: BHMS,MD(Repertary),MD(Organon of Medicine),MD(Materia Medica)

------------------------------------
I have tried the following , but could not achieve it.

        1) XmlDataSourceCourse.XPath = "/Institutes/Institute[InstituteName='" +         CollegeDDL.SelectedItem.Value + "']"
 
        2) XmlDataSourceCourse.XPath = "/Institutes/Institute[InstituteName='" +         ddlinstitute.SelectedItem.Value + "']/Course"
 
        3)XmlDataSourceCourse.XPath = "/Institutes/Institute[InstituteName='" + ddlinstitute.SelectedItem.Value + "']/Course/CourseName"
 

Anybody please help to format correct XPATH Expression to achive this.