This XSLT will do the thing:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:x="http://ws.wso2.org/dataservice" xmlns="http://ws.wso2.org/dataservice" exclude-result-prefixes="x" version="1.0">
<xsl:output indent="yes" method="xml" />
<xsl:template match="x:Standards">
<Standards namespace="{namespace-uri()}">
<xsl:apply-templates select=".//x:Standard" />
</Standards>
</xsl:template>
<xsl:template match="x:Standard">
<Standard>
<xsl:copy-of select="x:ProductID" />
<xsl:copy-of select="x:Prefix"/>
<xsl:copy-of select="x:SNumber"/>
<RelatedProducts>
<xsl:apply-templates select=".//x:RelatedProduct"/>
</RelatedProducts>
<xsl:copy-of select="x:S1"/>
<xsl:copy-of select="x:S2"/>
</Standard>
</xsl:template>
<xsl:template match="x:RelatedProduct">
<xsl:element name="RelatedProduct">
<xsl:element name="RelationType">
<xsl:value-of select="name(..)" />
</xsl:element>
<xsl:copy-of select="*"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
Result is:
<?xml version="1.0"?>
<Standards xmlns="http://ws.wso2.org/dataservice" namespace="http://ws.wso2.org/dataservice">
<Standard>
<ProductID>200057</ProductID>
<Prefix>ISO</Prefix>
<SNumber>1001</SNumber>
<RelatedProducts>
<RelatedProduct>
<RelationType>DraftProducts</RelationType>
<ProductID>1500163</ProductID>
</RelatedProduct>
<RelatedProduct>
<RelationType>ReferenceProducts</RelationType>
<ProductID>263973</ProductID>
<RelationId>708519</RelationId>
<Designation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</RelatedProduct>
<RelatedProduct>
<RelationType>ReferenceProducts</RelationType>
<ProductID>320056</ProductID>
<RelationId>934789</RelationId>
<Designation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</RelatedProduct>
<RelatedProduct>
<RelationType>RelatedIntProducts</RelationType>
<ProductID xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
<RelationId>116881</RelationId>
<Relationship>Identical</Relationship>
<Designation>NEN ISO 1001</Designation>
</RelatedProduct>
<RelatedProduct>
<RelationType>RelatedIntProducts</RelationType>
<ProductID>208076</ProductID>
<RelationId>116886</RelationId>
<Relationship>Identical</Relationship>
<Designation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</RelatedProduct>
</RelatedProducts>
<S1>1001</S1>
<S2>1986</S2>
</Standard>
<Standard>
<ProductID>200058</ProductID>
<Prefix>ISO</Prefix>
<SNumber>1002</SNumber>
<RelatedProducts>
<RelatedProduct>
<RelationType>DraftProducts</RelationType>
<ProductID>1500167</ProductID>
</RelatedProduct>
<RelatedProduct>
<RelationType>ReferenceProducts</RelationType>
<ProductID>263974</ProductID>
<RelationId>708519</RelationId>
<Designation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</RelatedProduct>
<RelatedProduct>
<RelationType>ReferenceProducts</RelationType>
<ProductID>320052</ProductID>
<RelationId>934754</RelationId>
<Designation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</RelatedProduct>
<RelatedProduct>
<RelationType>RelatedIntProducts</RelationType>
<ProductID xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
<RelationId>116837</RelationId>
<Relationship>Identical</Relationship>
<Designation>NEN ISO 1001</Designation>
</RelatedProduct>
<RelatedProduct>
<RelationType>RelatedIntProducts</RelationType>
<ProductID>208074</ProductID>
<RelationId>116843</RelationId>
<Relationship>Identical</Relationship>
<Designation xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</RelatedProduct>
</RelatedProducts>
<S1>1005</S1>
<S2>1983</S2>
</Standard>
</Standards>
2
solved Merge different products belong to each standard – V2 [duplicate]