First I would say that since you ultimately want documents rather than URIs, it would be more effective to use cts:search directly. You can add the "unfiltered" option if you want to avoid the cost of filtering, e.g.:
let $value1 := "antony"
let $value2 := "cse"
return
cts:search( doc(),
cts:element-query(xs:QName("P"),
cts:and-query((
cts:element-attribute-value-query(xs:QName("P"),xs:QName("name"),$value1),
cts:element-attribute-value-query(xs:QName("P"),xs:QName("value"),$value2)
))
), "unfiltered"
)//PS/P[@name eq "volume"]/@value
or, since you only care about /PS/P elements:
cts:search( doc()//PS/P,
cts:element-query(xs:QName("P"),
cts:and-query((
cts:element-attribute-value-query(xs:QName("P"),xs:QName("name"),"antony"),
cts:element-attribute-value-query(xs:QName("P"),xs:QName("value"),"cse")
))
), "unfiltered"
)[@name eq "volume"]/@value
To search within a collection, replace the doc() with collection("yourcollection"):
cts:search( collection("yourcollection")//PS/P,
cts:element-query(xs:QName("P"),
cts:and-query((
cts:element-attribute-value-query(xs:QName("P"),xs:QName("name"),"antony"),
cts:element-attribute-value-query(xs:QName("P"),xs:QName("value"),"cse")
))
), "unfiltered"
)[@name eq "volume"]/@value