...
<variables>
<variable name="global.defaultContext" type="string"/>
<variable name="user.firstName" type="string"/>
<variable name="characters" type="document">
<customer>
<id>dog1</id>
<name>Goofy</name>
<city>Toon Town</city>
</customer>
<customer>
<id>mouse2</id>
<name>Minnie</name>
<city>Toon Town</city>
</customer>
</variable>
<variable name="session.key1" type="string"/>
<variable name="session.customerInfo" type="document"/>
<variable name="session.dogInfo" type="document" />
</variables>
...
<invoke service="myService" operation="someQuery"
inputvariables="$global.defaultContext" .../>
...
<filter filterexpr="/customer[matches(firstname, $user.firstName )] inputvariable="$allCustomers" outputvariable="thisCustomer"/>
...
<assign literal="New York Giants" outputvariable="$session.key1"/>
<assign fromvariable="$characters"
outputvariable="$session.customerInfo"/>
<assign fromexpr="$session.customerInfo/customer[@id='dog1']"
outputvariable="$session.dogInfo"/>