Location Steps and Paths

Transcription

1 Locatio Steps ad Paths 3 INTHIS CHAPTER Uderstadig Locatio Steps ad Paths How do locatio paths work? We took a look at locatio paths i the overview i Chapter 1, where we saw that locatio paths look much like directory paths For example, you might store sectio oe of chapter oe of part oe of a ovel i a directory with this path if you re usig Widows: Uderstadig Locatio Steps ad Paths 63 Usig the XPath Axes 76 Creatig Compoud Locatio Paths 92 I Brief 95 \ovel\part1\sectio1\chapter1 or this path if you re usig Uix: /ovel/part1/sectio1/chapter1 The idea behid XPath locatio paths is very much the same except that, as we ll see i this chapter ad the ext, the XPath sytax ca get much more complex ad detailed tha directory paths Like directory paths, you build locatio paths out of idividual steps, called locatio steps, separated by / or // You use these steps to specify the data you wat, just as you use successive directories i a file path to get to the locatio of a file For example, i the XPath locatio path /library/book/title[2]/text(), we begi with a /, which matches the root ode of the documet, followed by, i order: The locatio step library, which matches the child <library> elemet of the root ode The locatio step book, which matches the child <book> elemet of the <library> elemet

2 64 CHAPTER 3 Locatio Steps ad Paths The locatio step title[2], which matches the secod <title> elemet of the <book> elemet text(), which matches the text i the <title> elemet I fact, the XPath locatio path /library/book/title[2]/text() uses abbreviated XPath sytax, which we re goig to see i this chapter Here s the full versio of this XPath locatio path, where the child elemet ature of each successive locatio step is spelled out: /child::library/child::book/child::title[positio()=2]/child::text Okay ow let s get to the details The Parts of a Locatio Step Each locatio step is made up of a axis, a ode test, ad zero or more predicates, like this (where the * symbol meas zero or more of ): axis :: ode-test [predicate]* For example, i the locatio step child::ame[positio() = 2], child is the ame of the axis (which you follow with ::), ame is the ode test ad [positio() = 2] is the predicate I this case, the child axis selects child odes of the ode you start at, which is the cotext ode We re goig to take a look at axes, ode tests, ad predicates i detail i this chapter This locatio step ca also be abbreviated, usig the abbreviated sytax we ll see i this chapter, as ame[2] (this works because the child axis is the default axis, ad whe you use positio predicates like [positio() = 2], XPath lets you abbreviate them as simply [2]) Locatio paths ca be made up of oe or more locatio steps, such as child::ame[positio() = 2]/child::firstName, which selects all the <firstname> elemets that are childre of the secod <ame> child elemet of the cotext ode This locatio path ca also be abbreviated as ame[2]/firstname Whe you start the locatio path (ot a locatio step) with / or //, the locatio path is called a absolute locatio path because you re specifyig the path from the root ode of the XML documet (just as startig a file path with / i Uix starts the path from the root directory ad makes the path a absolute oe) Otherwise, the locatio path is relative, startig with the cotext ode For example, take a look at this ode tree agai: root elemet: <library>

3 65 Uderstadig Locatio Steps ad Paths elemet: <book> elemet: <title> elemet: <title> text: I Love XPath text: XPath is the BEST Begiig a locatio path with / (or //, as we ll see) makes that path start with the documet s root ode, makig this a absolute locatio path ad makig the root ode the cotext ode for the first locatio step i the path To move to the child <library> elemet, you add the locatio step library like this: /library (usig uabbreviated sytax, that would be /child::library) That makes the cotext ode for the ext locatio step the <library> elemet To move to the <book> elemet startig from the <library> cotext ode, you add book (or child::book) to the locatio path like this: /library/book ad so o, all the way dow to the text i the secod <title> elemet, which you reach with /library/book/title[2]/text() These are all absolute locatio paths, startig from the root ode O the other had, if you ve got a cotext ode already set some XPath software lets you specify cotext odes your locatio paths ca be relative For example, if you ve set the cotext ode to the <library> elemet, the relative locatio path book/title[2]/text() will locate the text i the secod <title> elemet i the documet Now it s time to get systematic about our study of locatio steps, which we re goig to do by takig a look at what kid of axes, ode tests, ad predicates XPath are available XPath Axes We re goig to take a look at all 13 XPath 10 axes i this chapter For example, i the locatio step child::plaet, which refers to all <plaet> elemets that are childre of the cotext ode, child is the axis (ad as you ow kow, you ca also abbreviate this locatio step as plaet, because child is the default axis) Here are all the XPath 10 axes: The acestor axis holds the acestors of the cotext ode; the acestors of the cotext ode are the paret of cotext ode ad the paret s paret ad so forth, back to ad icludig the root ode The acestor-or-self axis holds the cotext ode ad the acestors of the cotext ode The attribute axis holds the attributes of the cotext ode The child axis holds the childre of the cotext ode The descedat axis holds the descedats of the cotext ode A descedat is a child or a child of a child ad so o

4 66 CHAPTER 3 Locatio Steps ad Paths The descedat-or-self axis cotais the cotext ode ad the descedats of the cotext ode The followig axis holds all odes i the same documet as the cotext ode that come after the cotext ode The followig-siblig axis holds all the followig sibligs of the cotext ode A siblig is a ode o the same level as the cotext ode The amespace axis holds the amespace odes of the cotext ode The paret axis holds the paret of the cotext ode The precedig axis cotais all odes that come before the cotext ode The precedig-siblig axis cotais all the precedig sibligs of the cotext ode A siblig is a ode o the same level as the cotext ode The self axis cotais the cotext ode Each XPath locatio step must specify a axis (or use the default child axis), as i this locatio path we ve already see: /child::library/child::book/child::title[2]/child::text You ca also see the various XPath axes listed i Table 31, which lists the support for these axes by XML processors i Iteret Explorer The XML processor i Iteret Explorer is called MSXML; MSXML 20 was the versio i Iteret Explorer 50, early versios of Iteret Explorer 60 used MSXML3, ad the curret versio is MSXML4 If you re usig the NET platform, your versio of MSXML is MSXMLNET TABLE 31 The XPath Axes AXIS ABBREVIATION MSXML2 MSXML3 MSXML4 MSXMLNET acestor x x x acestor-or-self x x x x x x child (default) x x x x descedat // x x x x descedat-or-self x x x x followig x x x followig-siblig x x x amespace x x x paret x x x x precedig x x x precedig-siblig x x x self x x x x

5 67 Uderstadig Locatio Steps ad Paths XPath Node Tests Whe you use a axis i a locatio step, you re tellig XPath where to look ad idetifyig a set of odes A ode test tells XPath which of the odes i that set you re iterested i There are a umber of ways to create ode tests You ca use ames of odes as ode tests, or the wildcard * to select elemet or attribute odes (ote especially that * matches oly elemets ad attributes, ot just ay kid of ode) For example, the locatio step child::*/child::ame selects all <ame> elemets that are gradchildre of the cotext ode To match attributes, you d use the attribute axis like this: attribute::* Besides ode ames ad the wildcard character, you ca also use these ode tests i XPath 10: The * wildcard character matches ay elemet or attribute ame A ame matches a ode with that ame (for example, plaet will match a <plaet> elemet) The commet() ode test selects commet odes The ode() ode test selects ay type of ode The processig-istructio() ode test selects a processig istructio ode You ca specify the ame of the processig istructio to select i the paretheses The text() ode test selects a text ode You ca see the XPath 10 ode tests i Table 32, alog with the XML processor versio that supports them i the Iteret Explorer TABLE 32 The XPath Node Tests AXIS MSXML2 MSXML3 MSXML4 MSXMLNET * x x x x ame x x x x commet() x x x x ode() x x x x processig-istructio() x x x x text() x x x x The ode test lets you specify what odes you wat to work with i a XPath locatio step For example, take a look at our sample ode tree: root elemet: <library>

6 68 CHAPTER 3 Locatio Steps ad Paths elemet: <book> elemet: <title> elemet: <title> text: I Love XPath text: XPath is the BEST You ca start at the root ode with /, ad the use the child axis ad the ode test library to move to the <library> elemet givig you the locatio path /child::library You ca see this at work i the XPath Visualiser i Figure 31 FIGURE 31 Usig the XPath locatio step /child::library Ad you ca move to the <book> elemet uder the <library> elemet with aother locatio step ivolvig this child axis ad a ode test like this: /child:library/child:book You ca see what this looks like i the XPath Visualiser i Figure 32 FIGURE 32 Usig the XPath locatio step /child::library/child::book

7 69 Uderstadig Locatio Steps ad Paths The ext level dow i the ode tree holds two <title> elemets, however What if we oly wat to work with the secod oe? If we used the locatio path /child::library/child::book/child::title, we d match both <title> elemets, so we eed more tha a ode test here we eed to use a predicate XPath Predicates The ext part of a locatio step, which follows the ode text, is the predicate A locatio step does t eed a predicate, but if you use a predicate, you ca specify eve more about the ode or odes you wat to match You ofte use oe of the built-i XPath fuctios i predicates For example, take a look at the locatio step child::plaet[positio() = 2] I this case, the predicate, which is always eclosed betwee [ ad ], is positio() = 2 This meas that the value the built-i XPath fuctio positio() returs must idicate that this is the secod <plaet> child i order for the locatio step to match (this locatio step ca also be abbreviated as plaet[2]) I this way, this predicate arrows dow the search from the ode-set of all <plaet> childre of the cotext ode dow to the secod <plaet> child Now we re i a positio to select the secod <title> elemet i our XML documet that has this ode tree: root elemet: <library> elemet: <book> elemet: <title> elemet: <title> text: I Love XPath text: XPath is the BEST To move to the secod <title> elemet, we ca use the locatio path /child::library/child::book/child::title[2], as you see i the XPath Visualiser i Figure 33 (this locatio path ca also be abbreviated as /library/book/title[2]) As you ca see, expressios i predicates ca let you arrow dow the search from a whole ode-set to just the odes you re lookig for Here s aother ode-test example to select the <title> elemet that cotais the text I Love XPath, you ca use this XPath locatio path with the text() ode test: /child::library/child::book/child::title[text()= I Love XPath ], as you see i Figure 34

8 70 CHAPTER 3 Locatio Steps ad Paths FIGURE 33 Usig the locatio step /child::library/child::book/child::title[2] FIGURE 34 Selectig a <title> elemet Now we re able to costruct XPath locatio paths like /child::library/child::book/ child::title[2] usig axes, ode tests, ad predicates Each part of a locatio step, the axis, ode test, ad predicate, arrows dow the set of odes you re workig with You ca also build up XPath expressios much as you ca locatio paths For example, the text() ode test will retur the text i a ode, so if you wat to extract the text of the <title> elemet, you ca use the XPath expressio /child::library/child::book/child::title[2]/text(), which evaluates ot to a ode-set, but to a text strig, XPath is the BEST, as you ca see i Figure 35 You ca use multiple predicates i the same locatio step for example, say that we added a laguage attribute to each <plaet> elemet i our plaetary data XML documet, as you see i ch03_01xml (see Listig 31)

9 71 Uderstadig Locatio Steps ad Paths FIGURE 35 Usig /child::library/child::book/child::title[2]/text() LISTING 31 Addig a Laguage Attribute (ch03_01xml) <?xml versio= 10 ecodig= utf-8?> <plaets> <plaet laguage= Eglish > <ame>mercury</ame> <mass uits= (Earth = 1) >0553</mass> <day uits= days >5865</day> <radius uits= miles >1516</radius> <desity uits= (Earth = 1) >983</desity> <distace uits= millio miles >434</distace><!--At perihelio--> </plaet> <plaet laguage= Eglish > <ame>veus</ame> <mass uits= (Earth = 1) >815</mass> <day uits= days >11675</day> <radius uits= miles >3716</radius> <desity uits= (Earth = 1) >943</desity> <distace uits= millio miles >668</distace><!--At perihelio--> </plaet> <plaet laguage= Eglish > <ame>earth</ame> <mass uits= (Earth = 1) >1</mass> <day uits= days >1</day>

10 72 CHAPTER 3 Locatio Steps ad Paths LISTING 31 Cotiued <radius uits= miles >2107</radius> <desity uits= (Earth = 1) >1</desity> <distace uits= millio miles >1284</distace><!--At perihelio--> </plaet> </plaets> What if we wated to reach the secod <plaet> elemet that has a laguage attribute set to Eglish? We could do that with a locatio path like this: /plaets/plaet[attribute::laguage = Eglish ][positio() = 2], as you see i Figure 36 I this way, you ca hadle multiple coditios with multiple predicates FIGURE 36 Usig /plaets/plaet[attribute::laguage = Eglish ][positio() = 2] Some Examples of XPath Locatio Paths There s othig like seeig all this at work to uderstad what s goig o, so here are a umber of locatio path examples: child::plaet Returs the <plaet> elemet childre of the cotext ode child::* Returs all elemet childre (* oly matches elemets, or attributes if you use it with the attribute axis) of the cotext ode child::text() Returs all text ode childre of the cotext ode

11 73 Uderstadig Locatio Steps ad Paths child::ode() Returs all the childre of the cotext ode, o matter what their ode type is attribute::uits Returs the uits attribute of the cotext ode descedat::plaet Returs the <plaet> elemet descedats of the cotext ode acestor::plaet Returs all <plaet> acestors of the cotext ode acestor-or-self::plaet Returs the <plaet> acestors of the cotext ode If the cotext ode is a <plaet> as well, also returs the cotext ode descedat-or-self::plaet Returs the <plaet> elemet descedats of the cotext ode If the cotext ode is a <plaet> as well, also returs the cotext ode self::plaet Returs the cotext ode if it is a <plaet> elemet child::ame/descedat::plaet Returs the <plaet> elemet descedats of the child <ame> elemets of the cotext ode child::*/child::plaet Returs all <plaet> gradchildre of the cotext ode / Returs the root ode (that is, the paret of the documet elemet) /descedat::plaet Returs all the <plaet> elemets i the documet /descedat::plaet/child::ame Returs all the <ame> elemets that have a <plaet> paret child::plaet[positio() = 3] Returs the third <plaet> child of the cotext ode child::plaet[positio() = last()] Returs the last <plaet> child of the cotext ode /descedat::plaet[positio() = 3] Returs the third <plaet> elemet i the documet child::plaets/child::plaet[positio() = 4 ]/child::ame[positio() = 3] Returs the third <ame> elemet of the fourth <plaet> elemet of the <plaets> elemet child::plaet[positio() > 3] Returs last() locatio path> last()> all the <plaet> childre of the cotext ode after the first three precedig-siblig::ame[positio() = 2] Returs the secod previous <ame> siblig elemet of the cotext ode child::plaet[attribute::color = RED ] Returs all <plaet> childre of the cotext ode that have a color attribute with value of RED

12 74 CHAPTER 3 Locatio Steps ad Paths child::plaet[attribute::color = RED ][positio() = 3] Returs the third <plaet> child of the cotext ode that has a color attribute with value of RED child::plaet[positio() = 3][attribute::color= RED ] Returs the third <plaet> child of the cotext ode, oly if that child has a color attribute with value of RED child::plaet[child::ame] Returs the <plaet> childre of the cotext ode that have <ame> childre As you ca see, some of this sytax is pretty ivolved, ad a little legthy to type However, there is a abbreviated form of XPath sytax, ad we ll look at that ext Usig XPath Abbreviated Sytax There are a umber of abbreviatios you ca take advatage of i XPath sytax Here are the rules: self::ode() ca be abbreviated as paret::ode() ca be abbreviated as child::odeame ca be abbreviated as odeame attribute::odeame ca be abbreviated /descedat-or-self::ode()/ ca be abbreviated as // You ca also abbreviate predicate expressios like [positio() = 3] as [3] Usig the abbreviated sytax makes XPath expressios a lot easier to write For example, attribute::uits ca be abbreviated you ca refer to the cotext ode itself as simply, ad you ca refer to the curret ode ad ay descedats as // The // sytax i particular is useful ad importat Take a look at ch03_01xml, for example, the XML documet where we re storig plaetary data I that XML documet, we have three <plaet> elemets as childre of the mai <plaets> elemet: <plaets> <plaet laguage= Eglish > <ame>mercury</ame> <mass uits= (Earth = 1) >0553</mass> <day uits= days >5865</day>

13 75 Uderstadig Locatio Steps ad Paths <plaet laguage= Eglish > <ame>veus</ame> <mass uits= (Earth = 1) >815</mass> <day uits= days >11675</day> <plaet laguage= Eglish > <ame>earth</ame> <mass uits= (Earth = 1) >1</mass> <day uits= days >1</day> To select all three <plaet> elemets, you ca use the absolute XPath expressio /plaets/plaet, which starts at the XML documet s root ode, fids the <plaets> elemet, ad the matches the three <plaet> child elemets That s fie if you kow exactly where i the XML documet the elemets you wat are ad so ca specify a direct path to them But you ca also use //plaet to select all three <plaet> elemets, because //plaet will fid the <plaet> elemets by checkig the root ode ad all descedats for <plaet> elemets That s the power of // whe you wat to search for odes that may be aywhere i a documet, use // How about some examples of locatio paths usig abbreviated sytax? Here are a umber of examples: plaet Returs the <plaet> elemet childre of the cotext ode * Returs all elemet childre of the cotext ode text() Returs all text ode childre of the cotext Returs the uits attribute of the cotext Returs all the attributes of the cotext ode plaet[3] Returs the third <plaet> child of the cotext ode plaet[first()] Returs the first <plaet> child of the cotext ode */plaet Returs all <plaet> gradchildre of the cotext ode /plaets/plaet[3]/ame[2] Returs the secod <ame> elemet of the third <plaet> elemet of the <plaets> elemet

14 76 CHAPTER 3 Locatio Steps ad Paths //plaet Returs all the <plaet> descedats of the root ode plaets//plaet Returs the <plaet> elemet descedats of the <plaets> elemet childre of the cotext ode //plaet/ame Returs all the <ame> elemets that have a <plaet> paret Returs the cotext ode itself //plaet Returs the <plaet> elemet descedats of the cotext ode Returs the paret of the cotext ode /@uits Returs the uits attribute of the paret of the cotext ode plaet[ame] Returs the <plaet> childre of the cotext ode that have <ame> childre plaet[ame= Veus ] Returs the <plaet> childre of the cotext ode that have <ame> childre with text equal to Veus Usig the XPath Axes There are 13 axes to master, ad we ll take a look at them here, complete with examples To uderstad how somethig like XPath works, there s o better way tha seeig it at work as much as possible We ll take a look at various examples usig XPath Visualiser, ad we ll also take a look at some examples usig the XPath axes with XSLT You do t really have to uderstad the XSLT at this poit you ca just pick out the XPath expressio iside the example But XSLT is importat whe workig with XPath, as we re goig to see i Chapter 5, ad here it will help us out whe XPath Visualiser ca t (as with the amespace axis, which XPath Visualiser does t display visually) We re already familiar with the child ad attribute axes, so we wo t itroduce them here, but we will itroduce all the other axes ow, begiig with the acestor axis Usig the acestor Axis The acestor axis cotais all the acestors of the cotext ode, icludig its parets, gradparets, great-gradparets, ad so o This axis always cotais the root ode (uless the cotext ode is the root ode) Here s a example usig XPath Visualiser I this case, we ll use the locatio path //plaet/day to select the <day> elemets i our plaetary data example, ch03_01xml The we ll work backward with the acestor axis to fid the <plaet> acestor of each <day> elemet like this: //plaet/day/acestor::plaet You ca see the results i Figure 37 (ote that we re oly searchig for <plaet> acestors with this locatio path, so oly <plaet> acestors are selected)

15 77 Usig the XPath Axes FIGURE 37 Usig the acestor axis Here s a example doig the same thig usig XSLT As discussed i Chapter 1, i XSLT you create a template with a <xsl:template> elemet to match odes I this case, we wat to match <day> elemets: <xsl:template match= day > Now we ll use a <xsl:for-each> elemet to loop over all acestors of the <day> elemet, usig the XPath acestor axis: <xsl:template match= day > <xsl:for-each select= acestor::* > </xsl:for-each> To display the ame of the acestor elemet, we ca use the XSLT <xsl:value-of> elemet We ca extract the ame of the curret plaet with the XPath expressio /ame, where selects the cotext ode Here s what that looks like i XSLT: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml />

16 78 CHAPTER 3 Locatio Steps ad Paths <xsl:template match= day > <xsl:for-each select= acestor::* > <xsl:value-of select= /ame /> </xsl:for-each> <xsl:template match= plaet > <xsl:apply-templates select= day /> </xsl:stylesheet> Ad here s the result whe you use this stylesheet o ch03_01xml as you ca see, we ve bee able to pick out the ames of the acestors of the <day> elemets i our documet: <?xml versio= 10 ecodig= utf-8?> Mercury Veus Earth Usig the acestor-or-self Axis The acestor-or-self axis cotais all the acestors of the cotext ode, ad the cotext ode itself That meas, amog other thigs, that this axis always cotais the root ode Here s a example usig XPath Visualiser I this case, we ll use this axis to select all acestors of <day> elemets, as well as the <day> elemet itself this way: /plaet/day/acestoror-self::* You ca see the results i Figure 38 FIGURE 38 Usig the acestor-or-self axis

17 79 Usig the XPath Axes Here s a example usig XSLT ad the acestor-or-self axis I this case, we re goig to add author attributes set to Thaddeus throughout our documet like this: <?xml versio= 10 ecodig= utf-8?> <?xml-stylesheet type= text/xml href= plaetsxsl?> <plaets author= Thaddeus > <plaet author= Thaddeus laguage= Eglish > <ame>mercury</ame> <mass uits= (Earth = 1) >0553</mass> <day author= Thaddeus uits= days >5865</day> <radius uits= miles >1516</radius> <desity uits= (Earth = 1) >983</desity> <distace uits= millio miles >434</distace><!--At perihelio--> </plaet> <plaet author= Thaddeus laguage= Eglish > <ame>veus</ame> <mass uits= (Earth = 1) >815</mass> <day uits= days >11675</day> <radius uits= miles >3716</radius> <desity uits= (Earth = 1) >943</desity> <distace uits= millio miles >668</distace><!--At perihelio--> </plaet> <plaet laguage= Eglish > <ame>earth</ame> <mass uits= (Earth = 1) >1</mass> <day uits= days >1</day> <radius uits= miles >2107</radius> <desity uits= (Earth = 1) >1</desity> <distace uits= millio miles >1284</distace><!--At perihelio--> </plaet> </plaets> Now say that you wat to list by ame all acestors of <day> elemets that have a author attribute as well as the curret <day> elemet if it has a author attribute To do that, you ca use the XPath locatio path acestor-or-self::*[@author], which matches all odes ad acestors that have a author attribute Here s what it looks like i XSLT: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml />

18 80 CHAPTER 3 Locatio Steps ad Paths <xsl:template match= day > <xsl:for-each select= acestor-or-self::*[@author] > <xsl:value-of select= local-ame() /> <xsl:text> </xsl:text> </xsl:for-each> <xsl:template match= plaet > <xsl:apply-templates select= day /> </xsl:stylesheet> Here s the result, showig the matchig acestors of all three <day> elemets that have author attributes, icludig the <day> elemet itself, which has a author attribute: <?xml versio= 10 ecodig= UTF-8?> plaets plaet day plaets plaet plaets Usig the descedat Axis The descedat axis cotais all the descedats of the cotext ode Note that this does ot iclude ay attributes or amespace odes Here s a example usig XPath Visualiser I this case, we ll select all descedats of <plaet> elemets with the locatio path //plaet/descedat::*, as you see i Figure 39 FIGURE 39 Usig the descedat axis

19 81 Usig the XPath Axes Here s a example usig XSLT I this case, we ll check a documet to see if it icludes a <plaet> elemet for Mercury, ad if so, we ll iclude this elemet i the result: <ifo>sorry, Mercury caot be foud at this time</ifo> To match Mercury s <plaet> elemet, all you have to do is to check whether ay text ode descedat of a <plaet> elemet holds the strig Mercury this way: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 10 xmls:xsl= > <xsl:output method= xml /> <xsl:template match= plaet[descedat::text()= Mercury ] > <ifo>sorry, Mercury caot be foud at this time</ifo> <xsl:template match= * > <xsl:apply-templates select= * /> </xsl:stylesheet> That s all it takes Here s the result, showig the <ifo> elemet: <?xml versio= 10 ecodig= utf-8?> <ifo>sorry, Mercury caot be foud</ifo> Usig the descedat-or-self Axis The descedat-or-self axis cotais all the descedats of the cotext ode, ad the cotext ode itself Note, however, that it does ot cotai ay attributes or amespace odes You ca see a example i Figure 310, where we re selectig all <plaet> elemets ad their descedats with the XPath locatio path //plaet/descedat-or-self::* Here s a example doig the same thig usig XSLT I this case, we ll use a XSLT template to match all <plaet> elemets ad the loop over all odes i the ode-set retured by usig the descedat-or-self axis, displayig each ode s ame: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 10 xmls:xsl= > <xsl:output method= xml />

20 82 CHAPTER 3 Locatio Steps ad Paths <xsl:template match= plaet > <xsl:for-each select= descedat-or-self::* > <xsl:value-of select= local-ame() /> <xsl:text> </xsl:text> </xsl:for-each> </xsl:stylesheet> FIGURE 310 Usig the descedat-or-self axis That s all it takes Here s the result, where we ve bee able to list the ame of all the descedats of <plaet> elemets, as well as the <plaet> elemets themselves, usig the descedat-or-self axis: <?xml versio= 10 ecodig= UTF-8?> plaet ame mass day radius desity distace plaet ame mass day radius desity distace plaet ame mass day radius desity distace Usig the followig Axis The followig axis cotais all odes that come after the cotext ode i documet order, excludig ay of the cotext ode s descedats ad also excludig attribute odes ad amespace odes You ca see a example i the XPath Visualiser i Figure 311, where we re usig this axis to select the followig elemets after the <mass> elemet i the first <plaet> elemet, usig the XPath locatio path /plaets/plaet[1]/mass/followig::*

21 83 Usig the XPath Axes FIGURE 311 Usig the followig axis to extract data Here s a example usig XSLT to do the same thig I this case, we re matchig the first <plaet> elemet i a XSLT template ad displayig the ames of the followig elemets: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml /> <xsl:template match= plaet[1] > <xsl:for-each select= mass/followig::* > <xsl:value-of select= local-ame() /> <xsl:text> </xsl:text> </xsl:for-each> <xsl:template match= * > <xsl:apply-templates select= * /> </xsl:stylesheet> Here s what the result looks like Note that we ve bee able to get all the elemets followig the <mass> elemet i the first <plaet> elemet, ad the all the followig elemets i the rest of the documet:

22 84 CHAPTER 3 Locatio Steps ad Paths <?xml versio= 10 ecodig= UTF-8?> day radius desity distace plaet ame mass day radius desity distace plaet ame mass day radius desity distace Usig the followig-siblig Axis The followig-siblig axis cotais all the followig sibligs of the cotext ode You ca see a example i the XPath Visualiser i Figure 312, where we re usig the XPath locatio path /plaets/plaet[1]/mass/followig-siblig::* to select all followig siblig odes of the <mass> elemet i the first <plaet> elemet FIGURE 312 Usig the followig-siblig axis Here s how this example works i XSLT; i this case, we re also matchig the first <plaet> elemet s <mass> elemet ad the gettig its followig siblig elemets: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml /> <xsl:template match= plaet[1] > <xsl:for-each select= mass/followig-siblig::* > <xsl:value-of select= local-ame() /> <xsl:text> </xsl:text> </xsl:for-each>

23 85 Usig the XPath Axes <xsl:template match= * > <xsl:apply-templates select= * /> </xsl:stylesheet> Here s the result as you ca see, we ve caught all the sibligs followig the <mass> elemet i the first <plaet> elemet: <?xml versio= 10 ecodig= UTF-8?> day radius desity distace Usig the amespace Axis The amespace axis cotais the amespace odes of the cotext ode ote that the axis will be empty uless the cotext ode is a elemet A elemet will have a amespace ode for Every attribute of the elemet whose ame starts with xmls: Every attribute of a acestor elemet whose ame starts xmls: (uless, of course, the elemet itself or a earer acestor redeclares the amespace) A xmls attribute, if the elemet, or some acestor, has a xmls attribute XPath Visualiser does t hadle this axis visually, so we ll rely o XSLT here Here, we ll add a XML amespace declaratio to the <plaets> elemet, usig the amespace like this: <?xml versio= 10 ecodig= utf-8?> <?xml-stylesheet type= text/xml href= plaetsxsl?> <plaets xmls= > <plaet> <ame>mercury</ame> <mass uits= (Earth = 1) >0553</mass> <day uits= days >5865</day> <radius uits= miles >1516</radius> <desity uits= (Earth = 1) >983</desity> <distace uits= millio miles >434</distace><!--At perihelio--> </plaet>

24 86 CHAPTER 3 Locatio Steps ad Paths I XSLT, we ca check the amespaces used i the <plaets> elemet like this: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml /> <xsl:template match= plaets > <xsl:value-of select= amespace::* /> </xsl:stylesheet> Ad here s the result, showig that we ca ideed pick out the amespace: <?xml versio= 10 ecodig= UTF-8?> Usig the paret Axis The paret axis cotais the paret (ad oly the paret) of the cotext ode, if there is oe You ca see a example i XPath Visualiser i Figure 313 Here, we re pickig out the paret elemets of all <day> elemets with the XPath locatio path //day/paret::* FIGURE 313 Usig the paret axis to extract data

25 87 Usig the XPath Axes Ad here s the same example i XPath I this case, we ll match all <day> elemets ad get the ames of their paret elemets Here s what it looks like: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml /> <xsl:template match= //day > <xsl:for-each select= paret::* > <xsl:value-of select= local-ame() /> <xsl:text> </xsl:text> </xsl:for-each> <xsl:template match= * > <xsl:apply-templates select= * /> </xsl:stylesheet> Ad here s the result: <?xml versio= 10 ecodig= UTF-8?> plaet plaet plaet USING THE ABBREVIATION Remember that you ca also use the abbreviatio to stad for the paret of the cotext ode Usig the precedig Axis The precedig axis cotais all odes that are before the cotext ode i documet order, excludig ay acestors of the cotext ode, ad also excludig attribute odes ad amespace odes Here s a example usig XPath Visualiser I this case, we ll select all elemets precedig the <desity> elemet i the first plaet elemet with the XPath locatio path //plaet[1]/desity/precedig::*, as you ca see i Figure 314 Let s give this axis a try i XSLT I this case, say that we wat to set the cotet of the <distace> elemet to the text This plaet is farther tha Mercury from the su if the curret plaet is ideed farther from the su tha Mercury Oe way to do that is to see if Mercury comes before the curret plaet i documet order, usig the precedig axis: <?xml versio= 10 ecodig= utf-8?> <xsl:stylesheet versio= 11 xmls:xsl= > <xsl:output method= xml />

26 88 CHAPTER 3 Locatio Steps ad Paths <xsl:template match= distace[precedig::*/ame= Mercury ] > <distace>this plaet is farther tha Mercury from the su</distace> <xsl:template ode() > <xsl:copy> <xsl:apply-templates ode() /> </xsl:copy> </xsl:stylesheet> FIGURE 314 Usig the precedig axis to select elemets If the curret plaet does come after Mercury, this example iserts the message i its <distace> elemet, as you see i this result: <?xml versio= 10 ecodig= utf-8?> <?xml-stylesheet type= text/xml href= plaetsxsl?> <plaets> <plaet> <ame>mercury</ame> <mass uits= (Earth = 1) >0553</mass> <day uits= days >5865</day> <radius uits= miles >1516</radius> <desity uits= (Earth = 1) >983</desity> <distace uits= millio miles >434</distace> <!--At perihelio--> </plaet>

27 89 Usig the XPath Axes <plaet> <ame>veus</ame> <mass uits= (Earth = 1) >815</mass> <day uits= days >11675</day> <radius uits= miles >3716</radius> <desity uits= (Earth = 1) >943</desity> <distace>this plaet is farther tha Mercury from the su</distace> <!--At perihelio--> </plaet> <plaet> <ame>earth</ame> <mass uits= (Earth = 1) >1</mass> <day uits= days >1</day> <radius uits= miles >2107</radius> <desity uits= (Earth = 1) >1</desity> <distace>this plaet is farther tha Mercury from the su</distace> <!--At perihelio--> </plaet> </plaets> Usig the precedig-siblig Axis The precedig-siblig axis cotais all the precedig sibligs of the cotext ode Note that if the cotext ode is a attribute ode or amespace ode, the precedig-siblig axis wo t hold aythig You ca see a example i the XPath Visualiser i Figure 315, where we re usig the XPath locatio path //plaet[2]/precedig-siblig::* to select all precedig sibligs of the secod <plaet> elemet Note that just the first <plaet> elemet is selected O the other had, if we had used //plaet[2]/precedig::*, ot oly would the first <plaet> elemet be selected, but all that elemet s child elemets would be selected as well Here s a more advaced example usig XSLT I this case, we ll replace the <distace> elemet i Mercury s <plaet> elemet with <distace>this plaet is the closest to the su</distace> If we re matchig <distace> elemets, how ca we make sure that we ve got Mercury s <distace> elemet? We ca check the curret <distace> elemet s precedig sibligs ad look for the text Mercury Here s what it looks like i XSLT: <?xml versio= 10?> <xsl:stylesheet versio= 10 xmls:xsl= > <xsl:output method= xml />

28 90 CHAPTER 3 Locatio Steps ad Paths <xsl:template match= distace[precedig-siblig::*= Mercury ] > <distace>this plaet is the closest to the su</distace> <xsl:template ode() > <xsl:copy> <xsl:apply-templates ode() /> </xsl:copy> </xsl:stylesheet> FIGURE 315 Usig the precedig-siblig axis to extract data Ad here s the result: <?xml versio= 10 ecodig= utf-8?> <?xml-stylesheet type= text/xml href= plaetsxsl?> <plaets> <plaet laguage= Eglish > <ame>mercury</ame> <mass uits= (Earth = 1) >0553</mass> <day uits= days >5865</day> <radius uits= miles >1516</radius> <desity uits= (Earth = 1) >983</desity> <distace>this plaet is the closest to the su</distace> <!--At perihelio--> </plaet>

29 91 Usig the XPath Axes <plaet laguage= Eglish > <ame>veus</ame> <mass uits= (Earth = 1) >815</mass> <day uits= days >11675</day> <radius uits= miles >3716</radius> <desity uits= (Earth = 1) >943</desity> <distace uits= millio miles >668</distace><!--At perihelio--> </plaet> <plaet laguage= Eglish > <ame>earth</ame> <mass uits= (Earth = 1) >1</mass> <day uits= days >1</day> <radius uits= miles >2107</radius> <desity uits= (Earth = 1) >1</desity> <distace uits= millio miles >1284</distace><!--At perihelio--> </plaet> </plaets> Usig the self Axis The self axis cotais just the cotext ode, ad you ca abbreviate self::ode() as This is a useful axis to kow about, because as you kow, if you omit the axis, the default is child::, but sometimes you wat to refer to the curret ode istead For example, [self::plaet] is true oly if the cotext ode is a <plaet> elemet You ca see a example usig this axis i XPath Visualiser i Figure 316, where we re usig the XPath locatio path //*[self::radius] to select <radius> elemets i ch03_01xml (this locatio path is equivalet to //radius) Here s a example usig XSLT I this case, we ll use oe template to match both <ame> ad <day> elemets i the same template We ca do that by matchig ame day i a template like this (more o how this works i the ext sectio): <xsl:template match= ame day > At this poit, we ve matched both <ame> ad <day> elemets but suppose that i the body of the template we actually wat to treat these elemets differetly To do that, we have to check if we re dealig with a <ame> elemet or a <day> elemet, which we ca do with the

30 92 CHAPTER 3 Locatio Steps ad Paths XSLT elemet <xsl:if>, where you assig the coditio to test to this elemet s test attribute Here s what it looks like i XSLT: <xsl:template match= ame day > <xsl:if test= self::ame > <xsl:value-of select= /> </xsl:if> <xsl:if test= self::day > <xsl:value-of select= /> <xsl:text> </xsl:text> <xsl:value-of /> </xsl:if> FIGURE 316 Usig the self axis to select <radius> elemets So ow we ve take a look at all 13 axes, from the acestor axis to the self axis Note that you ca combie locatio paths with the operator we ll take a closer look at that ow Creatig Compoud Locatio Paths I XPath, you ca combie locatio paths with the, or pipe character We ve already see that at work like this:

31 93 Creatig Compoud Locatio Paths <xsl:template match= ame day > You ca use ay kid of locatio paths with the pipe character, like this: <xsl:template match= ame/firstname day/author/lastname > Whe you use a compoud locatio path, each path is evaluated separately that is, the cotext ode for the first path does t affect the cotext ode for the other path Ad you re ot restricted to two paths; you ca coect as may as you like with pipes: <xsl:template match= ame/firstname day/author/lastname distace mass/kilograms > Whe it comes to predicates, however, the situatio is differet I XPath, you combie coditios i a predicate with the ad ad or operators For example, if you wated to match all <distace> elemets that have uits attributes set to millio miles ad laguage attributes set to Eglish, you could use the ad operator like this: <xsl:template match= distace[@uits= millio miles Eglish ] > <distace>this is the plaet Mercury, closest to the Su</distace> USING QUOTATION MARKS Notice the quotatio marks here to avoid cofusig the XSLT processor, we re usig sigle quotes to surroud the attribute values here, because the whole XPath expressio is surrouded i double quotes You could also use the or operator if you wated to match <distace> elemets that have uits attributes set to millio miles or laguage attributes set to Eglish, like this: <xsl:template match= distace[@uits= mil lio miles Eglish ] > <distace>this is the plaet Mercury, closest to the Su</distace>

32 94 CHAPTER 3 Locatio Steps ad Paths Here s aother example: child::*[self::ame or self::mass], which returs both the <ame> ad <mass> childre of the cotext ode You ca coect as may coditios i a predicate as you wat usig ad ad or Ad if it gets cofusig, you ca use paretheses like this: <xsl:template match= author[(@firstname= Cary ) ad (@lastname= Grat)] > <distace>this is the plaet Mercury, closest to the Su</distace> Note also that compoud locatio paths ca also have predicates, of course, icludig compoud predicates Nestig Predicates It s also legal to est predicates Here s how you might select all <project> elemets that have <ame> descedats that i tur have a precedig siblig <active> elemet: //project[descedat::ame[precedig-siblig::active]] You ca also est predicates whe usig compoud locatio paths ad eve compoud predicates Usig Predicates Without Operators The predicates we ve used so far usually use operators, as i the locatio step author[positio()=4], where we re usig the = operator (we ll see all the available operators i the ext chapter) However, you do t eed to use operators at all i predicates if you just wat to test for the existece of a ode For example, if you wat to fid all <otatio> elemets that cotai at least oe <author> elemet, you ca use this locatio path: //otatio[descedat::author] That s it for this chapter o locatio steps ad locatio paths We saw how XPath works with the data model itroduced i Chapter 2 by usig locatio paths, which are made up of locatio steps Each locatio step, i tur, is made up of a axis, a ode test, ad a predicate I Chapter 4, we re goig to get more details o creatig locatio paths as we see the operators ad fuctios you ca use i XPath predicates

33 95 I Brief I Brief Each locatio step is made up of a axis, a ode test, ad zero or more predicates A axis idicates how to search for odes Here are the XPath 10 axes: The child axis The attribute axis The acestor axis The acestor-or-self axis The descedat axis The descedat-or-self axis The followig axis The followig-siblig axis The amespace axis The paret axis The precedig axis The precedig-siblig axis The self axis You ca use these ode tests i XPath 10: The * wildcard character matches ay elemet or attribute ame A ame matches a ode with that ame (for example, plaet will match a <plaet> elemet) The commet() ode test selects commet odes The ode() ode test selects ay type of ode The processig-istructio() ode test selects a processig istructio ode The text() ode test selects a text ode Predicates are eclosed i [ ad ] ad may cotai ay valid XPath 10 expressio