Xpath how to get element by index AND attribute

Given this xml:

<mets:techMD ID="techMD014">
    <mets:mdWrap MDTYPE="PREMIS:OBJECT">
        <mets:xmlData>
            <premis:object
                    xsi:type="premis:file"
                    xsi:schemaLocation="info:lc/xmlns/premis-v2
                    http://www.loc.gov/standards/premis/v2/premis-v2-0.xsd">
                <premis:objectIdentifier>
                    <premis:objectIdentifierType
                     >filepath</premis:objectIdentifierType>
                    <premis:objectIdentifierValue
                     >bib1234_yyyymmdd_99_x_performance.xml</premis:objectIdentifierValue>
                </premis:objectIdentifier>
            </premis:object>
        </mets:xmlData>
    </mets:mdWrap>
</mets:techMD>
<mets:techMD ID="techMD015">
    <mets:mdWrap MDTYPE="PREMIS:OBJECT">
        <mets:xmlData>
            <premis:object
                    xsi:type="premis:representation"
                    xsi:schemaLocation="info:lc/xmlns/premis-v2
                    http://www.loc.gov/standards/premis/v2/premis-v2-0.xsd">
                <premis:objectIdentifier>
               开发者_如何学Python     <premis:objectIdentifierType
                     >local</premis:objectIdentifierType>
                    <premis:objectIdentifierValue
                     >bib1234_yyyymmdd_99_x</premis:objectIdentifierValue>
                </premis:objectIdentifier>
            </premis:object>
        </mets:xmlData>
    </mets:mdWrap>
</mets:techMD>

I would like to make a xpath query that takes both index and attribute into account. I.e can I combine these two into ONE query? (Its the stuff around the "object" element Im interested in):

//techMD/mdWrap[
   @MDTYPE=\'PREMIS:OBJECT\'
]/xmlData//object[1]/objectIdentifier/objectIdentifierValue

//techMD/mdWrap[
   @MDTYPE=\'PREMIS:OBJECT\'
]/xmlData//object[
   @xsi:type=\'premis:file\'
]/objectIdentifier/objectIdentifierValue

Thanks!

---

Just replace according part to:

object[@xsi:type='premis:file'][1]

if you want first object of those who have a given xsi:type value or

object[1][@xsi:type='premis:file']

if you want the first object, providing it has a given xsi:type value.