Tree Processing (DOM)

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1 XML Prcessing Tree Prcessing (DOM) Lecture "XML in Cmmunicatin Systems" Chapter 6 Dr.-Ing. Jesper Zedlitz Research Grup fr Cmmunicatin Systems Dept. f Cmputer Science Christian-Albrechts-University in Kiel

2 Recmmended Reading Lauren Wd, Arnaud Le Hrs, Vidur Appara et al.: Dcument Object Mdel (DOM) Level 1 Specificatin (Secnd Editin) Versin 1.0, W3C Wrking Draft 29 September, N. Luttenberger 2

3 Overview 1. Intrductin 2. Dcument Object Mdel (DOM) N. Luttenberger 3

4 Chapter 6.1 Intrductin

5 Intrductin Hw t give prgram cde access t XML dcuments? Applicatin Prgramming Interfaces (APIs) N. Luttenberger 5

6 Intrductin XML prcessing XML dcument XML prcessr (e.g. Xerces) Applicatin API N. Luttenberger 6

7 Intrductin XML prcessrs prvide the structure and cntents f XML dcuments t applicatins thrugh APIs Tree-based APIs prvide full parse tree t applicatin e.g., DOM W3C Recmmendatin (Dcument Object Mdel) Stream-based APIs ntify applicatin thrugh parsing events e.g., the SAX callback interfaces (Simple API fr XML) N. Luttenberger 7

8 Tree-based APIs <Envelpe> <Bdy> <add> <x>12</x> <x>38</x> <x>27</x> </add> </Bdy> </Envelpe> 5 KB Parser & Dc. Builder Envelpe Bdy add 200 KB tree prcessing x x x N. Luttenberger 8

9 Stream-based APIs <Envelpe> <Bdy> <add> <x>12</x> <x>38</x> <x>27</x> </add> </Bdy> </Envelpe> XML Parser begin("envelpe")... begin("x") cntent("12") end("x") stream prcessing... end("envelpe") N. Luttenberger 9

10 Tree vs. Stream Pr and cns tree prcessing but cnvenient tree navigatin straightfrward impl. f mdificatin peratins cnsumes 10 t 100 times mre memry than XML text tree building must be cmpleted befre applicatin prcessing starts stream prcessing but lw memry cnsumptin XML prcessing starts with first parsing event n internal dcument representatin fr navigatin and prcessing N. Luttenberger 10 lw verhead fr validatin f invalid dcuments

11 Chapter 6.2 Dcument Object Mdel (DOM)

12 Dcument Object Mdel (DOM) DOM What is it? With the DOM (Dcument Object Mdel), the W3C has defined a language- and platfrm-neutral view f XML dcuments much like the XML Infrmatin Set. DOM APIs exist fr a wide variety f predminantly bject-riented prgramming languages (Java, C++, C, Perl, Pythn, ). N. Luttenberger 12

13 Dcument Object Mdel (DOM) DOM What is it? DOM allws prgrams and scripts t build dcuments, t navigate their structure, t add, mdify r delete elements and cntent fr implementatins f querying, filtering, transfrmatin, rendering etc. applicatins One culd read DOM as "Directly Obtainable in Memry" N. Luttenberger 13

14 Dcument Object Mdel (DOM) Frm the Mzilla develper site "The Dcument Object Mdel (DOM) is a prgramming interface fr HTML and XML dcuments. It prvides a structured representatin f the dcument and it defines a way that the structure can be accessed frm prgrams s that they can change the dcument structure, style and cntent. The DOM prvides a representatin f the dcument as a structured grup f ndes and bjects that have prperties and methds. Essentially, it cnnects web pages t scripts r prgramming languages." N. Luttenberger 14

15 Dcument Object Mdel (DOM) Tw majr DOM cncepts XML dcument XML prcessr (e.g. Xerces) Applicatin API 1. An XML Prcessr ffering a DOM interface parses the XML input dcument, and cnstructs the cmplete XML dcument tree in memry. 2. The XML applicatin then issues DOM library calls t explre and manipulate the XML dcument, r generate new XML dcuments. N. Luttenberger 15

16 Dcument Object Mdel (DOM) Example: JavaScript All f the prperties, methds, and events available fr manipulating and creating web pages are rganized int bjects, e.g., the dcument bject represents the dcument itself, the table bject implements the special HTMLTableElement DOM interface fr accessing HTML tables, and s frth N. Luttenberger 16

17 Dcument Object Mdel (DOM) Example: JavaScript <html> <head> <script> // run this functin when the dcument is laded windw.nlad = functin() { // create a cuple f elements // in an therwise empty HTML page heading = dcument.createelement("h1"); heading_text = dcument.createtextnde("big Head!"); heading.appendchild(heading_text); dcument.bdy.appendchild(heading); } </script> </head> <bdy></bdy> </html> N. Luttenberger 17

18 Dcument Object Mdel (DOM) DOM structure mdel based n OO cncepts methds (t access r change bject s state) interfaces (declaratin f a set f methds) bjects (encapsulatin f data and methds) Rughly similar t the XPath/XSLT data mdel (t be discussed later) DOM "prduct" a parse tree Language-independence DOM interfaces defined in Interface Definitin Language (IDL) frm Crba Specificatin (OMG ) N. Luttenberger 18

19 Dcument Object Mdel (DOM) W3C DOM Specificatin secnd in the "XML family" f recmmendatins Level 1, W3C Rec, Sept (2 nd ed.) Level 2, W3C Rec, Nv Level 3, W3C Rec, April 2004 N. Luttenberger 19

20 Dcument Object Mdel (DOM) DOM Level 1 Basic representatin and manipulatin f dcument structure and cntent DOM Cre Interfaces Fundamental interfaces: basic interfaces t structured dcuments Extended interfaces (XML-specific): CDATASectin, DcumentType, Ntatin, Entity, EntityReference, PrcessingInstructin DOM HTML Interfaces mre cnvenient access t HTML dcuments N access t cntents f DTD N. Luttenberger 20

21 Dcument Object Mdel (DOM) DOM Level 2 adds supprt fr namespaces accessing elements by ID attribute values ptinal features interfaces t dcument views and style sheets an event mdel (fr user actins n elements) methds fr traversing the dcument tree and manipulating regins f dcument (e.g., selected by the user f an editr) N. Luttenberger 21

22 Dcument Object Mdel (DOM) DOM Level 3 adds Lading and writing f dcs N. Luttenberger 22

23 Dcument Object Mdel (DOM) Excerpt frm the inheritance hierarchy f nde bjects Nde Dcument Element Attribute Text Cmment PrcInstr NdeList NamedNdeMap interface t handle rdered lists f Ndes, such as the elements returned by the Element.getElementsByTagName methd interface t handle unrdered sets f ndes referenced by their name attribute, such as the attributes f an Element. N. Luttenberger 23

24 Dcument Object Mdel (DOM) DOM establishes tw basic types f peratins 1. Navigatin: the ability t traverse the nde hierarchy, and 2. Reference: the ability t access a cllectin f ndes by name. N. Luttenberger 24

25 Dcument Object Mdel (DOM) Navigatin The structure f the dcument determines the inheritance f element attributes. Thus, it is imprtant t be able t navigate amng the nde bjects representing parent and child elements. Given a nde, yu can find ut where it is lcated in the dcument structure mdel and yu can refer t the parent, child as well as siblings f this nde. This might be dne using the NdeList bject, which represents an rdered cllectin f ndes. N. Luttenberger 25

26 Dcument Object Mdel (DOM) Reference Example: a gallery page is filled with individual images. A unique name r ID can be assigned t each image using the NAME r ID attribute. It is pssible t create an index f image names r ID s by iterating ver a list f ndes. T reference an image the NamedNdeMap bject can be used, which represents an (unrdered) cllectin f ndes that can be accessed by name. N. Luttenberger 26

27 Dcument Object Mdel (DOM) Nde methds getndetype hasattributes getparentnde haschildndes getlastchild insertbefre(newchild,refchild) replacechild(newchild,ldchild) getpreviussibling getownerdcument getndevalue getattributes getchildndes getfirstchild 27

28 Dcument Object Mdel (DOM) Dcument methds getdcumentelement createattribute(name) createelement(tagname) createtextnde(data) getdctype() getelementbyid(idval) 28

29 Dcument Object Mdel (DOM) Element methds gettagname getattributende(name) setattributende(attr) remveattribute(name) getelementsbytagname(name) hasattribute(name) 29

30 Dcument Object Mdel (DOM) Object creatin in DOM Each DOM bject X lives in the cntext f a Dcument: X.getOwnerDcument() Objects implementing interface X are created by factry methds D.createX( ), where D is a Dcument bject. Examples: createelement("a"), createattribute("href"), createtextnde("hell!") Creatin and persistent saving f Dcuments left t be specified by implementatins. N. Luttenberger 30

31 DOM: Implementatins Java-based parsers e.g. IBM XML4J, Apache Xerces, Apache Crimsn MS IE5 brwser COM prgramming interfaces fr C/C++ and MS Visual Basic, ActiveX bject prgramming interfaces fr script languages XML::DOM (Perl implementatin f DOM Level 1) N. Luttenberger 31

32 Dcument Object Mdel (DOM) Cncluding remarks Inherent memry hunger f the DOM may lead t heavy swapping activity r even "ut-f-memry" failures. T remedy: Try t preprcess the input XML dcument t reduce its verall size. Use an XPath/XSLT prcessr t preselect interesting dcument regins, Or: Use a cmpletely different apprach t XML prcessing ( SAX). N. Luttenberger 32

Grammars for XML XML Information Set

Grammars for XML XML Information Set Grammars fr XML XML Infrmatin Set Lecture "XML in Cmmunicatin Systems" Chapter 2 Dr.-Ing. Jesper Zedlitz Research Grup fr Cmmunicatin Systems Dept. f Cmputer Science Christian-Albrechts-University in Kiel