XML and Databases. Outline. XPath. Outline - Lectures. XPath Data Model. Outline - Assignments. XPath. Sebastian Maneth NICTA and UNSW

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1 Outline XML n Dtses Leture 6 Noe Seleting Queries: XPth XPth Dt Moel: 7 types of noes 2. Simple Exmples 3. Lotion Steps n Pths 4. Vlue Comprison, n Other Funtions Sestin Mneth NICTA n UNSW CSE@UNSW -- Semester 1, XPth Query lnguge to selet ( sequene of) noes of n XML oument W3C Stnr Most importnt XML query lnguge: use in mny other stnrs suh s XQuery, XSLT, XPointer, XLink, Cve: version 2.0 is onsierly more expressive thn 1.0 We stuy XPth 1.0 Terminology: Inste of XPth query we often sy XPth expression. (An expression is the primry onstrution of the XPth grmmr; it mthes the proution Expr of the XPth grmmr.) Outline - Letures 1. Introution to XML, Enoings, Prsers 2. Memory Representtions for XML: Spe vs Aess Spee 3. RDBMS Representtion of XML 4. DTDs, Shems, Regulr Expressions, Amiguity 5. XML Vlition using Automt 6. Noe Seleting Queries: XPth 7. Tree Automt for Effiient XPth Evlution, Prllel Evlution 8..XPth Properties: kwr xes, ontinment test 9. Streming Evlution: how muh memory o you nee? 10. XPth Evlution using RDBMS 11. XSLT stylesheets n trnsform 12. XQuery XML query lnguge XPth 3 4 Outline - Assignments XPth Dt Moel 1. Re XML, using DOM prser. Crete oument sttistis. 2. SAX Prse into memory struture: Tree n DAG XPth Query Q XML oument D Evlute Q on D (in XPth t moel) sequene of result noes 3. Mp XML into RDBMS 20. April 4. XPth evlution 11. My 5. XPth into SQL Trnsltion 25. June Doument D is moele s tree. THERE ARE SEVEN TYPES OF NODES in the XPth Dt Moel: 7 noe types root noes element noes text noes ttriute noes nmespe noes proessing instrution noes omment noes 5 6 1

2 XPth Dt Moel XPth Dt Moel XPth Query Q XML oument D Evlute Q on D (in XPth t moel) sequene of result noes Unique IDs An element noe my hve unique ientifier (ID). Vlue of the ttriute tht is elre in the DTD s type ID. No two elements in oument my hve the sme unique ID. If n XML proessor reports two elements in oument s hving the sme unique ID (whih is possile only if the oument is invli) then the seon element in o. orer must e trete s not hving unique ID. Doument D is moele s tree. NOTE: If oument hs no DTD, then no element will hve unique ID. THERE ARE SEVEN TYPES OF NODES in the XPth Dt Moel: 7 noe types root noes element noes text noes ttriute noes nmespe noes proessing instrution noes omment noes for rest of leture: this is ALL you nee to know out XML noes! root noes element noes text noes ttriute noes nmespe noes proessing instrution noes omment noes for rest of leture: this is ALL you nee to know out XML noes! 7 8 Doument D is moele s tree. XPth Dt Moel For eh noe string-vlue n e etermine. (sometimes prt of the noe, sometimes ompute from esennts, sometimes expne-nme: lol nme + nmespe URI) There is n orer, oument orer, efine on ll noes. orrespons to the position of the first hrter of the XML repr of the noe, in the oument (fter entity expnsion) Attriute n nmespe noes pper efore the hilren of n element. Orer of ttriute n nmespe noes is implementtion-epenent Every noe (esies root) hs extly one prent (whih is root or n element noe) XPth Query Q XML oument D XPth Result Sequenes Evlute Q on D (in XPth t moel) sequene of result noes Orere in oument orer Contins no uplites 9 10 Simple Exmples Simple Exmples In revite XPth syntx. In revite syntx. Q0: / Doument: <i> <ook> <uthor>aiteoul</uthor> <uthor>hull</uthor> <uthor>vinu</uthor> <title>fountions of Dtses</title> <yer>1995</yer> </ook> <ook> <uthor>ullmnn</uthor> Selets the oument root (lwys the prent of the oument element) oument root is virtul n invisile, in this exmple. If <?xml version="1.0"?> is present, then it is returne (s first entry) in the result of Q0. <title>priniples of Dtse n Knowlege Bse Systems</title> <yer>1998</yer> </ook> </i> oument element, if lele i Q1: /i/ook/yer hil noes tht re lele ook Doument: <i> hil noes tht re lele yer <ook> <uthor>aiteoul</uthor> <uthor>hull</uthor> <uthor>vinu</uthor> <title>fountions of Dtses</title> <yer>1995</yer> </ook> <ook> <uthor>ullmnn</uthor> <title>priniples of Dtse n Knowlege Bse Systems</title> <yer>1998</yer> </ook> </i> Note XPth Evlutors usully return the full sutree of the selete noe

3 Simple Exmples In revite syntx. oument element, if lele i Q1: /i/ook/yer hil noes tht re lele ook Doument: <i> hil noes tht re lele yer <ook> <uthor>aiteoul</uthor> <uthor>hull</uthor> Result of query Q1 = <uthor>vinu</uthor> (element) noes N1, N2 <title>fountions of Dtses</title> <yer>1995</yer> sutree t N1 is <yer>1995</yer> </ook> n sutree t N2 is <yer>1998</yer> <ook> <uthor>ullmnn</uthor> <title>priniples of Dtse n Knowlege Bse Systems</title> <yer>1998</yer> </ook> </i> 13 Simple Exmples reltive to the In revite syntx. ontext-noe = root noe esennt or self noes Q2: //uthor hil noes tht re lele uthor Doument: <i> <ook> <uthor>aiteoul</uthor> <uthor>hull</uthor> <uthor>vinu</uthor> <title>fountions of Dtses</title> <yer>1995</yer> </ook> <ook> <uthor>ullmnn</uthor> <title>priniples of Dtse n Knowlege Bse Systems</title> <yer>1998</yer> </ook> </i> // is short for /esennt-or-self::noe()/. For exmple, //uthor is short for /esennt-or-self::noe()/hil::uthor 14 In revite syntx. Q2: //uthor Simple Exmples Desennt or self noes tht re lele uthor Doument: <i> <ook> <uthor>aiteoul</uthor> <uthor>hull</uthor> <uthor>vinu</uthor> <title>fountions of Dtses</title> <yer>1995</yer> </ook> <ook> <uthor>ullmn</uthor> reltive to the ontext-noe = root noe Result of query Q2 = sequene of (element) noes ( N1, N2, N3, N4 ) <title>priniples of Dtse n Knowlege Bse Systems</title> <yer>1998</yer> </ook> </i> // is short for /esennt-or-self::noe()/. For exmple, //uthor is short for /esennt-or-self::noe()/hil::uthor 15 In revite syntx. Q3: //// Simple Exmples -hil of -o. element e 16 In revite syntx. Simple Exmples In revite syntx. Simple Exmples Q3: //// -hil of -o. element Q3: //// -hil of -o. element ALL -noes in this sutree e ALL -noes in this sutree e

4 Simple Exmples Simple Exmples In revite syntx. Q4: /*/ In revite syntx. Q5: // In revite syntx. Simple Exmples In revite syntx. Arevitions, so fr An Axis Q6: //* / is revition for /hil:: A Noetest // is revition for /esennt-or-self::noe()/hil:: Chil n esennt-or-self re only 2 out of 12 possile xes. An Axis is sequene of noes. It is evlute reltive to ontext-noe. Other xes: esennt prent nestor-or-self nestor -siling preeing-siling ttriute preeing In revite syntx. Arevitions, so fr An Axis In revite syntx. Exmples: Preites / is revition for /hil:: Q7: //[./] hs -hil (ontext-noes re ll -noes ) A Noetest // is revition for /esennt-or-self::noe()/hil:: // is revition for /esennt-or-self::noe()/. is revition for self::noe().. is revition for prent::noe() Chil n esennt-or-self re only 2 out of 12 possile xes. An Axis is sequene of noes. It is evlute reltive to ontext-noe. Other xes: esennt prent nestor-or-self nestor -siling preeing-siling ttriute preeing

5 Exmples: Preites Exmples: Preites In revite syntx. Q8: //[./]/ hs -hil In revite syntx. Q9: //[./]//.. hs -hil selet prent(s) of ontext-noe(s) prent(s) of the ontext-noe(s) All -hilren of the ontext-noe(s) Q9 selets -noes tht hve -hil AND -hil Exmples: Preites Exmples: Preites In revite syntx. Q9: //[./]//.. hs -hil selet prent(s) of ontext-noe(s) In revite syntx. Q9: //[./]//.. hs -hil selet prent(s) of ontext-noe(s) prent(s) of the ontext-noe(s) prent(s) of the ontext-noe(s) Q9 selets -noes tht hve -hil AND -hil More iret wy: //[./ n./] (sme s //[./] on *this* tree..!) Q9 selets -noes tht hve -hil AND -hil More iret wy: //[./ n./] (sme s //[./] on *this* tree..!) Exmples: Preites Exmples: Preites (or Filters ) In revite syntx. Q9: //[]//.. hs -hil selet prent(s) of ontext-noe(s) prent(s) of the ontext-noe(s) In revite syntx. //[ n ] evlutes to true/flse A Filter Q9 selets -noes tht hve -hil AND -hil More iret wy: //[ n ] (sme s //[./] on *this* tree..!) -noes tht hve -hil AND -hil We o not nee./ ::noe()/hil:: equivlent to

6 Exmples: Preites (or Filters ) Exmples: Preites In revite syntx. In revite syntx. //[ n ] evlutes to true/flse A Filter Question How to only selet the other -noe? //[ n ] evlutes to true/flse A Filter Question How to only selet the other -noe? Cn use not( ) in filter! Cn use not( ) in filter! Mny more possiilities, of ourse: //[prent::] //[../../] //[../] //[not()] oes not hve -hil //[not()] CAVE: wht oes //[../] give?? Exmples: Preites Exmples: Preites In revite syntx. In revite syntx. //[ n ] evlutes to true/flse A Filter Question How to only selet the other -noe? //[ n ] evlutes to true/flse A Filter Question How to only selet the other -noe? Cn use not( ) in filter! Mny more possiilities, of ourse: //[prent::] //[../../] //[../] Cn use not( ) in filter! Mny more possiilities, of ourse: //[prent::] //[../../] //[../] //[not()] CAVE: wht oes //[../] give?? //[not()] n you sy -noe tht hs only -hilren? Exmples: Preites Exmples: Preites In revite syntx. In revite syntx. //[ n ] evlutes to true/flse A Filter Question How to only selet the other -noe? //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] not the se tht ll hilren re not lele hols if n only if Cn use not( ) in filter! Mny more possiilities, of ourse: //[prent::] //[../../] //[../] ll hilren re lele //[not()] n you sy -noe tht hs only -hilren? YES! nees it of logi //[not(hil::*[not(self::)])]

7 Exmples: Preites Exmples: Preites In revite syntx. In revite syntx. //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] not the se tht ll hilren re not lele not the se tht ll hilren re not lele hols if n only if hols if n only if ll hilren re lele ll hilren re lele Duplite elimintion //[not()]//.. ontext-noes for prent seletion (/..) ontext-noes Duplite elimintion for nestor seletion //[not()]//nestor::* Exmples: Preites Exmples: Preites In revite syntx. In revite syntx. //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] not the se tht ll hilren re not lele not the se tht ll hilren re not lele hols if n only if hols if n only if ll hilren re lele ll hilren re lele Duplite elimintion mye //*[.//[not()]] Duplite elimintion mye //*[.//[not()]] No.. //[not()]//nestor::* //[not()]//nestor::* How to selet the -noe? Equivlent one, without use of nestor?? No use of nestor? Exmples: Preites Exmples: Preites In revite syntx. In revite syntx. //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] //[not()] sme s.. on this tree //[not(hil::*[not(self::)])] not the se tht ll hilren re not lele not the se tht ll hilren re not lele hols if n only if hols if n only if ll hilren re lele ll hilren re lele Duplite elimintion mye //*[.//[not()]] No.. Duplite elimintion mye //*[.//[not()]] No.. //[not()]//nestor::* No use of nestor? How to selet the -noe? //*[esennt-or-self::[not()]] 41 //[not()]//nestor::* How to selet the -noe? //*[.//[not()] or not(hil::*[not(self::)]) n./*] only -hilren hs hil (not lef) 42 7

8 XPth Query Q XML oument D More Detils Evlute Q on D (in XPth t moel) sequene of result noes Lotion Steps & Pths A Lotion Pth is sequene of Lotion Steps Lotion Pths [1] LotionPth ::= ReltiveLotionPth AsoluteLotionPth Initil Context will e is root noe [2] AsoluteLotionPth ::= '/' ReltiveLotionPth? AreviteAsoluteLotionPth NOT orret (t lest not for intermeite expr s) An expression evlutes to n ojet, whih hs one of the following four si types noe-set (n unorere olletion of noes w/o uplites) oolen (true or flse) numer ( floting-point numer) string ( sequene of UCS hrters) [3] ReltiveLotionPth ::= Step ReltiveLotionPth '/' Step AreviteReltiveLotionPth Lotion Steps [4] Step ::= AxisSpeifier NoeTest Preite* AreviteStep [5] AxisSpeifier ::= AxisNme ':: AreviteAxisSpeifier Lotion Steps & Pths A Lotion Pth is sequene of Lotion Steps A Lotion Step is of the form xis :: noetest [ Filter_1 ] [ Filter_2 ] [ Filter_n ] Lotion Steps & Pths A Lotion Pth is sequene of Lotion Steps A Lotion Step is of the form xis :: noetest [ Filter_1 ] [ Filter_2 ] [ Filter_n ] Filters (k preites, (filter) expressions) evlute to true/flse XPth queries, evlute with ontext-noe = urrent noe Boolen opertors: n, or Empty string/sequene re onverte to flse Filters (k preites, (filter) expressions) evlute to true/flse text() noetest: * or noe-nme (oul e expne nmespes) or omment() proessing -instrution(in) noe() Exmple hil::text() selet ll text noe hilren of the ontext noe the noetest noe() is true for ny noe. ttriute::* selet ll ttriutes of the ontext noe Lotion Steps & Pths Lotion Steps & Pths A Lotion Pth is sequene of Lotion Steps Axis = sequene of noes (is evlute reltive to ontext-noe) A Lotion Step is of the form xis :: noetest [ Filter_1 ] [ Filter_2 ] [ Filter_n ] Filters (k preites, (filter) expressions) evlute to true/flse text() noetest: * or noe-nme (oul e expne nmespes) or omment() proessing 12 Axes -instrution(in) Forwr Axes: Bkwr Axes: noe() In o orer hil esennt-or-self esennt -siling prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 47 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 48 8

9 Lotion Steps & Pths Lotion Steps & Pths Axis = sequene of noes (is evlute reltive to ontext-noe) Axis = sequene of noes (is evlute reltive to ontext-noe) In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 49 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 50 Lotion Steps & Pths Lotion Steps & Pths Axis = sequene of noes (is evlute reltive to ontext-noe) Axis = sequene of noes (is evlute reltive to ontext-noe) In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 51 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 52 Lotion Steps & Pths Lotion Steps & Pths Axis = sequene of noes (is evlute reltive to ontext-noe) Axis = sequene of noes (is evlute reltive to ontext-noe) In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 53 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 54 9

10 Lotion Steps & Pths Lotion Steps & Pths Axis = sequene of noes (is evlute reltive to ontext-noe) Axis = sequene of noes (is evlute reltive to ontext-noe) In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 55 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 56 Lotion Steps & Pths Lotion Steps & Pths Axis = sequene of noes (is evlute reltive to ontext-noe) Axis = sequene of noes (is evlute reltive to ontext-noe) In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 57 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 58 Lotion Steps & Pths Lotion Steps & Pths Axis = sequene of noes (is evlute reltive to ontext-noe) Axis = sequene of noes (is evlute reltive to ontext-noe) nestor preeing self esennt following In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 59 In o orer Forwr Axes: hil esennt-or-self esennt -siling Bkwr Axes: prent nestor nestor-or-self preeing preeing-siling ttriute reverse o orer 60 10

11 Context of n XPth evlution: Lotion Pth Evlution (1) ontext-noe (2) ontext position n size (oth non-negtive integers) (3) set of vrile inings (= mppings from vrile nmes to vlues) (4) funtion lirry (= mpping from funtion nmes to funtions) (5) set of nmespe elrtions (tw: ontext position is ontext size) Applition etermines the Initil Context. If pth strts with /, then Initil Context hs ontext-noe = root noe ontext-position = ontext-size = 1 61 Lotion Pth Semntis A Lotion Pth P is sequene of Lotion Steps _1 :: n_1 [ F_1_1 ] [ F_1_2 ] [ F_1_n1 ] / _2 :: n_2 [ F_2_1 ] [ F_2_2 ] [ F_2_n2 ] / _m :: n_m [ F_m_1 ] [ F_m_2 ] [ F_m_nm] S0 = initil sequene of ontext-noes (1) (to eh) ontext-noe N in S0, pply xis _1: gives sequene S1 of noes (2) remove from S1 ny noe M for whih test n_1 evlutes to flse ny of filters F_1_1,,F_1_n1 evlute to flse. Apply steps (1)&(2) for step 2, to otin from S1 the sequene S2 3, S2 S3 m S{m-1} Sm = result of P 62 No Looking Bk Attriute Axis Bkwr Axes re not neee!! How to test ttriute noes Exmples possile to rewrite every XPth query into n equivlent one tht oes not use kwr xes. Very nie result! Cn you see how this oul e one? We sw n exmple of removing nestor xis. But, of ourse the rewritten query must e the sme ON EVERY possile tree!! = 1 = 2 = 1 = 1.0 //ttriute::* Result: ="1" ="1" ="2" ="1.0" Rememer, these re just NODEs. //ttriute::*/. gives sme result Questions how muh lrger oes the query get, when you remove ll kwr xis? Is this useful for effiient query evlution?! An //ttriute::/.. gives < ="1"></>< ="2"></></></></> < ="2"></></></> < ="1.0"></></></> How to test ttriute vlues Attriute Axis & Vlue Tests Exmples How to test ttriute vlues Attriute Axis & Vlue Tests Exmples numer (flot) omprison //*[ttriute::=1] //*[ttriute::=1] (selets the two re noes) (selets the two re noes) = 1 = 1 = 1.0 = 1 = 1 = 1.0 Wth out //*[ttriute::= 1 ] only gives //*[ttriute::= 1.0 ] only gives = 2 = 2 string omprison

12 How to test ttriute vlues Attriute Axis & Vlue Tests Exmples numer (flot) omprison //*[ttriute::=1] (selets the two re noes) Wth out = 1 //*[ttriute::= 1 ] only gives = 1 = 1.0 //*[ttriute::= 1.0 ] only = 2 string omprison ttriute:: is revite How to test ttriute vlues Attriute Axis & Vlue Tests Exmples numer (flot) omprison //*[ttriute::=1] (selets the two re noes) Wth out = 1 //*[ttriute::= 1 ] only gives = 1 = 1.0 //*[ttriute::= 1.0 ] only = 2 string omprison ttriute:: is revite //*[@!="1"] selets oth -noes //*[@>1] selets only left -noe //*[@=//@] selets wht?? (hint: = is string omp. here) Tests in Filters Text Noes or n =,!= <=, <, >=, > The opertors re ll left ssoitive. For exmple, 3 > 2 > 1 is equivlent to (3 > 2) > 1, whih evlutes to flse. But, 3 > 2 > 0.9 evlutes to true. Cn you see why? For two strings u,v Boolen true oere to flot 1.0 How test text noes & vlues = 1 = 1 = 1.0 //text() Result: foo foo Br //*[text()= foo ] Result: the two re noes u<=v u<v u>=v u>v Alwys return flse! Unless oth u n v re numers. [ 1.0 >= 1 ] evlutes to true. = 2 foo foo r Question: Wht is the result for //*[text()=///text()] Useful Funtions (on Boolens) oolen(ojet):oolen Converts rgument into true/flse: numer is true if it is not equl to zero (or NN) noe-set is true if it is non-empty string is true if its length is non-zero - for other ojets, onversion epens on type not(true)=flse, not(flse)=true true():oolen flse():oolen ( oolen mens {true/flse}) lng(string):oolen Returns true if lnguge speifie y xml:lng ttriutes is sme s string ount Counts numer or results = 1 Useful Funtions (on Noe Sets) = 1 = 2 foo foo r /[ount(//*[text()=///text()])=2] Wht is the result? = 1.0 Useful even for use with self-xis: hil::*[self::hpter or self::ppenix] hpter or ppenix hilren of ontext noe

13 Useful Funtions (on Noe Sets) Useful Funtions (on Noe Sets) ount Counts numer or results /[ount(//*[text()=///text()])=2] ount Counts numer or results /[ount(//*[text()=///text()])=2] Wht is the result? Wht is the result? Sme result s: Sme result s: = 1 /[ount(//*[text()="foo"]) > ount(//*[text()="r"])] = 1 /[ount(//*[text()="foo"]) > ount(//*[text()="r"])] = 1 = 1.0 = 1 = 1.0 = 2 foo foo r = 2 foo foo r Wht is the result for: //[ount()=0] (sme s //[not()]) Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext = 1 = 1 = 1.0 //*[position()=2] = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 2 = 2 foo foo r foo foo r Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 2 = 2 //*[position()=lst()] //*[position()=lst()-1] foo foo r foo foo r

14 Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 2 = 2 foo foo r //*[position()=lst()-1 n./text()= foo ] foo foo r //*[position()=lst()-1 n./text()= foo ] 79 Useful: hil::*[self::hpter or self::ppenix][position()=lst()] selets the lst hpter or ppenix hil of the ontext noe 80 Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 1 = 1 = 1.0 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] = 2 = 2 foo foo r //*[position()=lst()-1 n./text()= foo ] foo foo r //*[position()=lst()-1 n./text()= foo ] */*[position()=1]/*[position()=2]/*[position()=2] */*[position()=1]/*[position()=2]/*[position()=2] llows solute lotion of ny noe ( l Dewey) 81 Arevition: */*[1]/*[2]/*[2] 82 Useful Funtions (on Noe Sets) Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext Returns ontext-position from the evl. ontext = 1 = 1 = 1.0 = 2 //*[position()=2] //*[position()=2 n../../] Sme s //*[position()=2 n./] ooks ook ook ook ook lst 20 How o you selet the lst 20 ook-hilren of ooks? foo foo r //*[position()=lst()-1 n./text()= foo ] */*[position()=1]/*[position()=2]/*[position()=2] Arevition: */*[1]/*[2]/*[2] Wht is result for //*[./*[2]/*[2]]

15 Useful Funtions (on Noe Sets) lst() returns ontex-size from the evlution ontext Returns ontext-position from the evl. ontext Useful Funtions (on Noe Sets) lst():numer returns ontex-size from the evlution ontext :numer eturns ontext-position from the evl. Context ooks ook ook ook ook lst 20 How o you selet the lst 20 ook-hilren of ooks? /ooks/ook[position()>lst()-20] i(ojet):noe-set i( foo ) selets the element with unique ID foo lol-nme(noe-set?):string returns the lol prt of the expne-nme of the noe nmespe-uri(noe-set?):string returns the nmespe URI of the expne-nme of the noe nme(noe-set?):string returns string ontining QNme representing the expne-nme of the noe Useful Funtions (on Noe Sets) Useful Funtions (on Noe Sets) Noes hve n ientity XPth 2.0 hs muh lerer omprison opertors!! Creful with equlity ( = ) XPth 2.0 hs muh lerer omprison opertors!! <> <>tt</> <>tt</> </> //[*[1]=*[2]] gives empty result. But: //[ontins(*[1],*[2])] gives the -noe. Different noes! Sorry. This is wrong. Equlity ( = ) is se on string vlue of noe! Gives lso -noe string-vlue ( tt ) is ontine in tt <> <> <>re</> <>green</> <>lue</> </> <> <>yellow</> <>ornge</> <>green</> </> </> //[/ = /] selets -noe!!! Sorry. This is wrong. Equlity ( = ) is se on string vlue of noe! Gives lso -noe there exists noe in the noe set for / with sme string vlue s noe in noe set / Useful Funtions (on Noe Sets) Useful Funtions (Strings) Creful with equlity ( = ) XPth 2.0 hs muh lerer omprison opertors!! The string-vlue of n element noe is the ontention of the string-vlues of ll text noe esennts in oument orer. <> <> <>re</> <>green</> <>lue</> </> <> <>yellow</> <>ornge</> <>green</> </> </> //[/ = /] selets -noe!!! Sorry. This is wrong. Equlity ( = ) is se on string vlue of noe! Gives lso -noe there exists noe in the noe set for / with sme string vlue s noe in noe set / = 1 = 1 = 1.0 = 2 foo foo r //*[.="foo"] //*[.= foor ] Wht out //[/!= /]

16 Useful Funtions (Strings) The string-vlue of n element noe is the ontention of the string-vlues of ll text noe esennts in oument orer. //*[.="foo"] //*[.= foor ] Useful Funtions (Strings) The string-vlue of n element noe is the ontention of the string-vlues of ll text noe esennts in oument orer. //*[.="foo"] //*[.= foor ] = 1 = 1 = 1.0 = 2 foo foo r ont(st_1, st_2,, st_n) = st_1 st_2 st_n strtswith(, ) = true ontins( r, ) = true sustring-efore("1999/04/01","/") = sustring-fter("1999/04/01","19") = 99/04/01 sustring("12345",2,3) = 234 string-length( foo ) = 3 normlize-spe( foo r ) = foo r trnslte( r","","abc") = BAr returns the first rgument string with ourrenes of hrters in the seon rgument string reple y the hrter t the orresponing position in the thir rgument string NOTE: The trnslte funtion is not suffiient solution for se onversion in ll lnguges Wht is the result to this: //*[ontins(.,"r")] Useful Funtions (Numers) Disply Numer Result numer(ojet):numer Opertors on Numers +,-,*,iv,mo Converts rgument to numer - the oolen true is onverte to 1, flse is onverte to 0 - string tht onsists of optionl whitespe followe y n optionl minus sign followe y Numer followe y whitespe is onverte to the IEEE 754 numer tht is nerest to the mthemtil vlue represente y the string. sum(noe-set):numer returns sum, for eh noe in the rgument noe-set, of the result of onverting the string-vlues of the noe to numer floor(numer):numer returns lrgest integer tht is not greter thn the rgument eiling(numer):numer returns the smllest integer tht is not less thn the rgument roun(numer):numer returns integer losest to the rgument. (if there re 2, tke ove: roun(0.5)=1 n roun(-0.5)=0 //*[text()=(7 mo (ount(//)+2))]/text() k n n n Use n Disply Numer Result XPth Query Evlution //*[text()=7 mo ((ount(//)+2)]/text() How to implement? How expensive? omplexity? k Wht re the most iffiult queries? n n n n Next time Effiient Algorithms: whih queries run how fst? First, fous on nvigtionl queries: only /, //, lel-test, [ filters ] (tehniques for vlue omprison/queries lrey well-known from rel. DB s ) Similr for ritrry lrge numers / oolens, noe-sets Try it

17 ontext noe mens yer 2003 Experiments with urrent systems Doument: <> </> </> </> Xpth Query (reltive to ): hil::*/prent::*/hil::*/ prent::*/hil::* Next 4 slies from Georg Gottlo n Christoph Koh "XPth Query Proessing". Invite tutoril t DBPL Tree of noes visite is of size Q O( D )!!! exponentil! qurti Doument: <></></></> Core Xpth on Xln n XT Queries: //prent::// prent::/ Core Xpth on Mirosoft IE6: polynomil omine omplexity, qurti t omplexity XPth Query Evlution Full XPth on IE6: Exponentil omine omplexity! Exponentil query omplexity Stti Methos (use, e.g., for Query Optimiztion ) Given Xpth queries Q1, Q2: Is result set of Q1 inlue in result set of Q2? Are result sets equl? Is their intersetion empty? for ll possile ouments (proly we will look t this in Leture 8 or 9)

18 Simple Exmples Is //[ount()=ount(*)] equivlent to //[not(hil::*[not(self::)])] END Leture 6 on ll possile trees?