XPATH有助于选择元素(XPATH help selecting elements)

所以我有这个XML数据库

<uni>  <subjects> <subject code="XYZ111"> <title>Java for housewives</title> <credits>6</credits> <laboratories> <laboratory num="lab1"> <date>12-MAR-2009</date> <topics> <topic>variables</topic> <topic>constants</topic> </topics> <description>Declarations of variables and constants</description> </laboratory> <laboratory num="lab2"> <date>12-APR-2009</date> <topics> <topic>expressions</topic> </topics> <description>Types of expressions</description> </laboratory> <laboratory num="lab3"> <date>12-MAY-2009</date> <topics> <topic>conditionals</topic> <topic>loops</topic> </topics> <description>Control statements</description> </laboratory> </laboratories> </subject> <subject code="XYZ235"> <title>Database systems for politicians</title> <credits>6</credits> <laboratories> <laboratory num="lab1"> <date>10-JAN-2001</date> <topics> <topic>classes</topic> <topic>associations</topic> <topic>properties</topic> </topics> <description>Conceptual modeling</description> </laboratory> <laboratory num="lab2"> <date>10-JAN-2002</date> <topics> <topic>relational tables</topic> <topic>primary keys</topic> <topic>foreign keys</topic> </topics> <description>Relational data model</description> </laboratory> </laboratories> </subject> <subject code="XYZ987"> <title>Ethics for car dealers</title> <credits>6</credits> </subject> <subject code="XYZ101"> <title>Programming for mathematicians</title> <credits>6000</credits> <laboratories> <laboratory num="lab1"> <date>10-JAN-2002</date> <topics> <topic>abstract algebra</topic> </topics> <description>Hilbert spaces of programming languages</description> </laboratory> <laboratory num="lab2"> <date>13-MAY-2002</date> <topics> <topic>topology</topic> </topics> <description>Theory of homothopy</description> </laboratory> </laboratories> </subject> <subject code="ZZZ777"> <title>Cooking</title> <credits>5</credits> <laboratories/> </subject> <subject code="ZZZ778"> <title>Dancing</title> <credits>5</credits> <laboratories/> </subject> <subject code="ABC123"> <title>General theory of everything</title> <credits>4</credits> <laboratories> <laboratory num="lab1"> <date>20-JAN-2012</date> <topics> <topic>space</topic> </topics> <description>Nothing really interesting</description> </laboratory> </laboratories> </subject> </subjects>  <enrolments> <enrolment snum="d2345" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>20</time> <IP>16.23.234.002</IP> <lab-enrolments> <laboratory num="lab1"/> </lab-enrolments> </enrolment> <enrolment snum="d2346" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>2</time> <IP>16.23.234.003</IP> <lab-enrolments> <laboratory num="lab1"/> </lab-enrolments> </enrolment> <enrolment snum="d2347" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>10</time> <IP>16.23.234.003</IP> </enrolment> <enrolment snum="d2348" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>20</time> <IP>16.23.234.025</IP> </enrolment> <enrolment snum="d6767" code="ABC123"> <date>13-DEC-2011</date> <status>valid</status> <time>5</time> <IP>16.23.234.202</IP> </enrolment> <enrolment snum="d2345" code="ZZZ778"> <date>14-DEC-2007</date> <status>valid</status> <time>10</time> <IP>16.23.234.402</IP> </enrolment> <enrolment snum="d6767" code="ZZZ777"> <date>12-SEP-2005</date> <status>valid</status> <time>15</time> <IP>16.23.234.202</IP> </enrolment> <enrolment snum="d2330" code="XYZ101"> <date>01-JAN-2002</date> <status>valid</status> <time>3</time> <IP>16.23.234.203</IP> <lab-enrolments> <laboratory num="lab1"/> <laboratory num="lab2"/> </lab-enrolments> </enrolment> <enrolment snum="d2349" code="XYZ101"> <date>01-JAN-2002</date> <status>valid</status> <time>7</time> <IP>16.23.234.202</IP> <lab-enrolments> <laboratory num="lab1"/> <laboratory num="lab2"/> </lab-enrolments> </enrolment> <enrolment snum="d2341" code="XYZ101"> <date>01-JAN-2002</date> <status>valid</status> <time>6</time> <IP>16.23.234.201</IP> <lab-enrolments> <laboratory num="lab1"/> </lab-enrolments> </enrolment> <enrolment snum="d6767" code="XYZ101"> <date>01-JAN-2002</date> <status>provisional</status> <time>5</time> <IP>16.23.234.002</IP> </enrolment> <enrolment snum="d6767" code="XYZ235"> <date>31-DEC-2000</date> <status>provisional</status> <time>30</time> <IP>16.23.234.602</IP> </enrolment> </enrolments> </uni>

我正试图找到包含抽象代数实验室的主题标题。到目前为止，这是我能想出的最好的答案，但它找不到匹配：/ / //uni/subjects/subject/laboratories/laboratory/topics/topic[text()="abstract algebra"]

So I have this XML database

<uni>  <subjects> <subject code="XYZ111"> <title>Java for housewives</title> <credits>6</credits> <laboratories> <laboratory num="lab1"> <date>12-MAR-2009</date> <topics> <topic>variables</topic> <topic>constants</topic> </topics> <description>Declarations of variables and constants</description> </laboratory> <laboratory num="lab2"> <date>12-APR-2009</date> <topics> <topic>expressions</topic> </topics> <description>Types of expressions</description> </laboratory> <laboratory num="lab3"> <date>12-MAY-2009</date> <topics> <topic>conditionals</topic> <topic>loops</topic> </topics> <description>Control statements</description> </laboratory> </laboratories> </subject> <subject code="XYZ235"> <title>Database systems for politicians</title> <credits>6</credits> <laboratories> <laboratory num="lab1"> <date>10-JAN-2001</date> <topics> <topic>classes</topic> <topic>associations</topic> <topic>properties</topic> </topics> <description>Conceptual modeling</description> </laboratory> <laboratory num="lab2"> <date>10-JAN-2002</date> <topics> <topic>relational tables</topic> <topic>primary keys</topic> <topic>foreign keys</topic> </topics> <description>Relational data model</description> </laboratory> </laboratories> </subject> <subject code="XYZ987"> <title>Ethics for car dealers</title> <credits>6</credits> </subject> <subject code="XYZ101"> <title>Programming for mathematicians</title> <credits>6000</credits> <laboratories> <laboratory num="lab1"> <date>10-JAN-2002</date> <topics> <topic>abstract algebra</topic> </topics> <description>Hilbert spaces of programming languages</description> </laboratory> <laboratory num="lab2"> <date>13-MAY-2002</date> <topics> <topic>topology</topic> </topics> <description>Theory of homothopy</description> </laboratory> </laboratories> </subject> <subject code="ZZZ777"> <title>Cooking</title> <credits>5</credits> <laboratories/> </subject> <subject code="ZZZ778"> <title>Dancing</title> <credits>5</credits> <laboratories/> </subject> <subject code="ABC123"> <title>General theory of everything</title> <credits>4</credits> <laboratories> <laboratory num="lab1"> <date>20-JAN-2012</date> <topics> <topic>space</topic> </topics> <description>Nothing really interesting</description> </laboratory> </laboratories> </subject> </subjects>  <enrolments> <enrolment snum="d2345" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>20</time> <IP>16.23.234.002</IP> <lab-enrolments> <laboratory num="lab1"/> </lab-enrolments> </enrolment> <enrolment snum="d2346" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>2</time> <IP>16.23.234.003</IP> <lab-enrolments> <laboratory num="lab1"/> </lab-enrolments> </enrolment> <enrolment snum="d2347" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>10</time> <IP>16.23.234.003</IP> </enrolment> <enrolment snum="d2348" code="ABC123"> <date>12-DEC-2011</date> <status>dropped</status> <time>20</time> <IP>16.23.234.025</IP> </enrolment> <enrolment snum="d6767" code="ABC123"> <date>13-DEC-2011</date> <status>valid</status> <time>5</time> <IP>16.23.234.202</IP> </enrolment> <enrolment snum="d2345" code="ZZZ778"> <date>14-DEC-2007</date> <status>valid</status> <time>10</time> <IP>16.23.234.402</IP> </enrolment> <enrolment snum="d6767" code="ZZZ777"> <date>12-SEP-2005</date> <status>valid</status> <time>15</time> <IP>16.23.234.202</IP> </enrolment> <enrolment snum="d2330" code="XYZ101"> <date>01-JAN-2002</date> <status>valid</status> <time>3</time> <IP>16.23.234.203</IP> <lab-enrolments> <laboratory num="lab1"/> <laboratory num="lab2"/> </lab-enrolments> </enrolment> <enrolment snum="d2349" code="XYZ101"> <date>01-JAN-2002</date> <status>valid</status> <time>7</time> <IP>16.23.234.202</IP> <lab-enrolments> <laboratory num="lab1"/> <laboratory num="lab2"/> </lab-enrolments> </enrolment> <enrolment snum="d2341" code="XYZ101"> <date>01-JAN-2002</date> <status>valid</status> <time>6</time> <IP>16.23.234.201</IP> <lab-enrolments> <laboratory num="lab1"/> </lab-enrolments> </enrolment> <enrolment snum="d6767" code="XYZ101"> <date>01-JAN-2002</date> <status>provisional</status> <time>5</time> <IP>16.23.234.002</IP> </enrolment> <enrolment snum="d6767" code="XYZ235"> <date>31-DEC-2000</date> <status>provisional</status> <time>30</time> <IP>16.23.234.602</IP> </enrolment> </enrolments> </uni>

And I'm trying to find the titles of subjects that include laboratories on abstract algebra. So far this is the best answer I could come up with, but it doesn't find a match :/ //uni/subjects/subject/laboratories/laboratory/topics/topic[text()="abstract algebra"]