[xslt] To compare two elements(string type) in XSLT?

i am new to XSLT ,can any one please suggest to me how to compare two elements coming from xml as string their values are:

<OU_NAME>Vision Operations</OU_NAME> --XML code
<OU_ADDR1>90 Fifth Avenue</OU_ADDR1> --XML code

<xsl:choose>
    <xsl:when test="OU_NAME='OU_ADDR1'"> --comparing two elements coming from XML
        <!--remove if  adrees already contain  operating unit name
            <xsl:value-of select="OU_NAME"/> <fo:block/>-->
        <xsl:if test="OU_ADDR1 !='' ">
            <xsl:value-of select="OU_ADDR1"/>
            <fo:block/>
        </xsl:if>
        <xsl:if test="LE_ADDR2 !='' ">
            <xsl:value-of select="OU_ADDR2"/>
            <fo:block/>
        </xsl:if>
        <xsl:if test="LE_ADDR3 !='' ">
            <xsl:value-of select="OU_ADDR3"/>
            <fo:block/>
        </xsl:if>
        <xsl:if test="OU_TOWN_CITY !=''">
            <xsl:value-of select="OU_TOWN_CITY"/>,
            <fo:leader leader-pattern="space" leader-length="2.0pt"/>
        </xsl:if>
        <xsl:value-of select="OU_REGION2"/>
        <fo:leader leader-pattern="space" leader-length="3.0pt"/>
        <xsl:value-of select="OU_POSTALCODE"/>
        <fo:block/>
        <xsl:value-of select="OU_COUNTRY"/>
    </xsl:when>
    <xsl:otherwise>
        <xsl:value-of select="OU_NAME"/>
        <fo:block/>
        <xsl:if test="OU_ADDR1 !='' ">
            <xsl:value-of select="OU_ADDR1"/>
            <fo:block/>
        </xsl:if>
        <xsl:if test="LE_ADDR2 !='' ">
            <xsl:value-of select="OU_ADDR2"/>
            <fo:block/>
        </xsl:if>
        <xsl:if test="LE_ADDR3 !='' ">
            <xsl:value-of select="OU_ADDR3"/>
            <fo:block/>
        </xsl:if>
        <xsl:if test="OU_TOWN_CITY !=''">
            <xsl:value-of select="OU_TOWN_CITY"/>,
            <fo:leader leader-pattern="space" leader-length="2.0pt"/>
        </xsl:if>
        <xsl:value-of select="OU_REGION2"/>
        <fo:leader leader-pattern="space" leader-length="3.0pt"/>
        <xsl:value-of select="OU_POSTALCODE"/>
        <fo:block/>
        <xsl:value-of select="OU_COUNTRY"/>
    </xsl:otherwise>
</xsl:choose>

First of all, the provided long code:

    <xsl:choose>
        <xsl:when test="OU_NAME='OU_ADDR1'">   --comparing two elements coming from XML             
            <!--remove if  adrees already contain  operating unit name <xsl:value-of select="OU_NAME"/> <fo:block/>-->
            <xsl:if test="OU_ADDR1 !='' ">
                <xsl:value-of select="OU_ADDR1"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="LE_ADDR2 !='' ">
                <xsl:value-of select="OU_ADDR2"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="LE_ADDR3 !='' ">
                <xsl:value-of select="OU_ADDR3"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="OU_TOWN_CITY !=''">
                <xsl:value-of select="OU_TOWN_CITY"/>,
                <fo:leader leader-pattern="space" leader-length="2.0pt"/>
            </xsl:if>
            <xsl:value-of select="OU_REGION2"/>
            <fo:leader leader-pattern="space" leader-length="3.0pt"/>
            <xsl:value-of select="OU_POSTALCODE"/>
            <fo:block/>
            <xsl:value-of select="OU_COUNTRY"/>
        </xsl:when>
        <xsl:otherwise>
            <xsl:value-of select="OU_NAME"/>
            <fo:block/>
            <xsl:if test="OU_ADDR1 !='' ">
                <xsl:value-of select="OU_ADDR1"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="LE_ADDR2 !='' ">
                <xsl:value-of select="OU_ADDR2"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="LE_ADDR3 !='' ">
                <xsl:value-of select="OU_ADDR3"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="OU_TOWN_CITY !=''">
                <xsl:value-of select="OU_TOWN_CITY"/>,
                <fo:leader leader-pattern="space" leader-length="2.0pt"/>
            </xsl:if>
            <xsl:value-of select="OU_REGION2"/>
            <fo:leader leader-pattern="space" leader-length="3.0pt"/>
            <xsl:value-of select="OU_POSTALCODE"/>
            <fo:block/>
            <xsl:value-of select="OU_COUNTRY"/>
        </xsl:otherwise>
    </xsl:choose>

is equivalent to this, much shorter code:

<xsl:if test="not(OU_NAME='OU_ADDR1)'">
              <xsl:value-of select="OU_NAME"/>
        </xsl:if>
            <xsl:if test="OU_ADDR1 !='' ">
                <xsl:value-of select="OU_ADDR1"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="LE_ADDR2 !='' ">
                <xsl:value-of select="OU_ADDR2"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="LE_ADDR3 !='' ">
                <xsl:value-of select="OU_ADDR3"/>
                <fo:block/>
            </xsl:if>
            <xsl:if test="OU_TOWN_CITY !=''">
                <xsl:value-of select="OU_TOWN_CITY"/>,
                <fo:leader leader-pattern="space" leader-length="2.0pt"/>
            </xsl:if>
            <xsl:value-of select="OU_REGION2"/>
            <fo:leader leader-pattern="space" leader-length="3.0pt"/>
            <xsl:value-of select="OU_POSTALCODE"/>
            <fo:block/>
            <xsl:value-of select="OU_COUNTRY"/>

Now, to your question:

how to compare two elements coming from xml as string

In Xpath 1.0 strings can be compared only for equality (or inequality), using the operator = and the function not() together with the operator =.

$str1 = $str2

evaluates to true() exactly when the string $str1 is equal to the string $str2.

not($str1 = $str2)

evaluates to true() exactly when the string $str1 is not equal to the string $str2.

There is also the != operator. It generally should be avoided because it has anomalous behavior whenever one of its operands is a node-set.

Now, the rules for comparing two element nodes are similar:

$el1 = $el2

evaluates to true() exactly when the string value of $el1 is equal to the string value of $el2.

not($el1 = $el2)

evaluates to true() exactly when the string value of $el1 is not equal to the string value of $el2.

However, if one of the operands of = is a node-set, then

 $ns = $str

evaluates to true() exactly when there is at least one node in the node-set $ns1, whose string value is equal to the string $str

$ns1 = $ns2

evaluates to true() exactly when there is at least one node in the node-set $ns1, whose string value is equal to the string value of some node from $ns2

Therefore, the expression:

OU_NAME='OU_ADDR1'

evaluates to true() only when there is at least one element child of the current node that is named OU_NAME and whose string value is the string 'OU_ADDR1'.

This is obviously not what you want!

Most probably you want:

OU_NAME=OU_ADDR1

This expression evaluates to true exactly there is at least one OU_NAME child of the current node and one OU_ADDR1 child of the current node with the same string value.

Finally, in XPath 2.0, strings can be compared also using the value comparison operators lt, le, eq, gt, ge and the inherited from XPath 1.0 general comparison operator =.

Trying to evaluate a value comparison operator when one or both of its arguments is a sequence of more than one item results in error.