sdpl 2002notes 3: xml processor interfaces1 3. xml processor apis n how can applications manipulate...

SDPL 2002 Notes 3: XML Processor Interfaces 1

3. XML Processor APIs3. XML Processor APIs

How can applications manipulate How can applications manipulate structured documents?structured documents?– An overview of document parser interfacesAn overview of document parser interfaces

3.1 SAX: an event-based interface3.1 SAX: an event-based interface

3.2 DOM: an object-based interface3.2 DOM: an object-based interface

3.3 JAXP: Java API for XML Processing3.3 JAXP: Java API for XML Processing


Document Parser InterfacesDocument Parser Interfaces

Every XML application contains some kind of a Every XML application contains some kind of a parserparser– editors, browsers editors, browsers – transformation/style engines, DB loaders, ...transformation/style engines, DB loaders, ...

XML parsers are becoming standard tools of XML parsers are becoming standard tools of application development frameworksapplication development frameworks– JDK v. 1.4 contains JAXP, with its default parser JDK v. 1.4 contains JAXP, with its default parser

(Apache Crimson)(Apache Crimson)

(See, e.g., Leventhal, Lewis & Fuchs: Designing XML (See, e.g., Leventhal, Lewis & Fuchs: Designing XML Internet Applications, Chapter 10, and Internet Applications, Chapter 10, and D. Megginson: Events vs. Trees)D. Megginson: Events vs. Trees)


Tasks of a ParserTasks of a Parser

Document instance decompositionDocument instance decomposition– elements, attributes, text, processing instructions, elements, attributes, text, processing instructions,

entities, ...entities, ... VerificationVerification

– well-formedness checking well-formedness checking » syntactical correctness of XML markupsyntactical correctness of XML markup

– validation (against a DTD or Schema)validation (against a DTD or Schema) Access to contents of the DTDAccess to contents of the DTD

– not always supportednot always supported– SAX 2.0 Extensions provide info of declarations to SAX 2.0 Extensions provide info of declarations to

applicationsapplications


Document Parser InterfacesDocument Parser Interfaces

I: Event-based interfacesI: Event-based interfaces– Command line and ESIS interfacesCommand line and ESIS interfaces

» Element Structure Information Set, traditional Element Structure Information Set, traditional interface to stand-alone SGML parsersinterface to stand-alone SGML parsers

– Event call-back interfaces: SAXEvent call-back interfaces: SAX

II: Tree-based (object model) interfacesII: Tree-based (object model) interfaces– W3C DOM RecommendationW3C DOM Recommendation


Command-line ESIS interfaceCommand-line ESIS interface

ApplicationApplication

SGML/XML ParserSGML/XML Parser

CommandCommandline callline call

ESISESISStreamStream

<A<A </A></A>Hi!Hi!

(A(A

i="1"i="1">>

Ai CDATA 1Ai CDATA 1

-Hi!-Hi!)A)A


Event Call-Back InterfacesEvent Call-Back Interfaces

Application implements a set of Application implements a set of callback callback methodsmethods for handling parse events for handling parse events– parser notifies the application by method callsparser notifies the application by method calls– method parameters qualify events further method parameters qualify events further

» element type nameelement type name» names and values of attributesnames and values of attributes» values of content strings, …values of content strings, …

Idea behind ‘‘SAX’’ (Simple API for XML)Idea behind ‘‘SAX’’ (Simple API for XML)– an industry standard API for XML parsersan industry standard API for XML parsers– could think as “could think as “SSerial erial AAccess ccess XXML”ML”


An event call-back applicationAn event call-back application

Application Main Application Main RoutineRoutine

startDocument()startDocument()

startElement()startElement()

characters()characters()

Parse(Parse())

Callback

Callback

Routines

Routines

endElement()endElement() <A i="1"><A i="1"> </A></A>Hi!Hi!

"A",[i="1"]"A",[i="1"]

"Hi!""Hi!"

"A""A"<?xml version='1.0'?><?xml version='1.0'?>


Object Model InterfacesObject Model Interfaces

Application interacts with an object-oriented Application interacts with an object-oriented representation ofrepresentation of– the parserthe parser– the document the document parse treeparse tree consisting of objects like consisting of objects like

documentdocument, , element, attribute, textelement, attribute, text, …, … Abstraction level higher than in event based Abstraction level higher than in event based

interfaces; more powerful access interfaces; more powerful access – to descendants, following siblings, …to descendants, following siblings, …

Drawback: Higher memory consumptionDrawback: Higher memory consumption


An Object-Model Based ApplicationAn Object-Model Based Application

ApplicationApplication

ParserParserObjectObject

In-Memory In-Memory Document Document

RepresentationRepresentationParseParse

Access/Access/ModifyModify

BuildBuild

DocumentDocument

i=1i=1AA

"Hi!""Hi!"

<A i="1"><A i="1"> </A></A>Hi!Hi!


3.1 The SAX Event Callback API3.1 The SAX Event Callback API

A de-facto industry standardA de-facto industry standard– NotNot an official standard or W3C Recommendation an official standard or W3C Recommendation– Developed by members of the xml-dev mailing listDeveloped by members of the xml-dev mailing list– Version 1.0 in May 1998, Vers. 2.0 in May 2000Version 1.0 in May 1998, Vers. 2.0 in May 2000– NotNot a parser, but a common interface for many a parser, but a common interface for many

different parsers (like JDBC is a common interface different parsers (like JDBC is a common interface to various RDBs)to various RDBs)

Supported directly by major XML parsersSupported directly by major XML parsers– most Java based and free: Sun JAXP, IBM most Java based and free: Sun JAXP, IBM

XML4J, Oracle's XML Parser for Java, Apache XML4J, Oracle's XML Parser for Java, Apache Xerces; MSXML (in IE 5), James Clark's XPXerces; MSXML (in IE 5), James Clark's XP


SAX 2.0 InterfacesSAX 2.0 Interfaces

Interplay between an application and a SAX-Interplay between an application and a SAX-conformant parser specified in terms of conformant parser specified in terms of interfaces interfaces (i.e., collections of methods)(i.e., collections of methods)

Classification of SAX interfaces:Classification of SAX interfaces:– Parser-to-application (or call-back) interfacesParser-to-application (or call-back) interfaces

» to attach special behaviour to parser-generated eventsto attach special behaviour to parser-generated events

– Application-to-parserApplication-to-parser» to use the parserto use the parser

– AuxiliaryAuxiliary» to manipulate parser-provided informationto manipulate parser-provided information


Call-Back InterfacesCall-Back Interfaces

Implemented by Implemented by applicationapplication to override default to override default behaviour (of ignoring any event quietly)behaviour (of ignoring any event quietly)– ContentHandlerContentHandler

» methods to process document parsing eventsmethods to process document parsing events

– DTDHandlerDTDHandler» methods to receive notification of unparsed external methods to receive notification of unparsed external

entities and their notations declared in the DTDentities and their notations declared in the DTD

– ErrorHandlerErrorHandler» methods for handling parsing errors and warningsmethods for handling parsing errors and warnings

– EntityResolverEntityResolver» methods for customised processing of external entity methods for customised processing of external entity

references references


Application-to-Parser InterfacesApplication-to-Parser Interfaces

Implemented by Implemented by parserparser (or its SAX driver): (or its SAX driver):

– XMLReaderXMLReader» methods to allow the application to invoke the parser and methods to allow the application to invoke the parser and

to register objects that implement call-back interfacesto register objects that implement call-back interfaces

– XMLFilterXMLFilter» interface to connect several XMLReaders in a row as a interface to connect several XMLReaders in a row as a

sequence of filterssequence of filters


SAX 2.0: Auxiliary InterfacesSAX 2.0: Auxiliary Interfaces

AttributesAttributes– methods to access a list of attributes methods to access a list of attributes

LocatorLocator– methods for locating the origin of parse events (e.g. methods for locating the origin of parse events (e.g.

systemID, line and column numbers, say, for reporting systemID, line and column numbers, say, for reporting semantic errors controlled by the application) semantic errors controlled by the application)


The The ContentHandlerContentHandler Interface Interface

Methods for receiving information of general Methods for receiving information of general document events. (See API documentation for a document events. (See API documentation for a complete list):complete list):

setDocumentLocator(Locator locator)setDocumentLocator(Locator locator) – Receive an object for locating the origin of SAX document Receive an object for locating the origin of SAX document

events (e.g. for reporting semantic errors controlled by the events (e.g. for reporting semantic errors controlled by the application) application)

startDocument();startDocument(); endDocument()endDocument() – notification of the beginning/end of a document. notification of the beginning/end of a document.

startElement(String namespaceURI, startElement(String namespaceURI, String localname, String qName,String localname, String qName,

Attributes atts);Attributes atts);endElement( … ) endElement( … ) similar (without attributes)similar (without attributes)– parameters support parameters support namespacesnamespaces


Namespaces in SAX: ExampleNamespaces in SAX: Example

<xsl:stylesheet version="1.0" <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns="http://www.w3.org/TR/xhtml1/strict"> xmlns="http://www.w3.org/TR/xhtml1/strict"> <xsl:template match="/"> <xsl:template match="/"> <html> <html>

<xsl:value-of select="//total"/><xsl:value-of select="//total"/> </html> </html> </xsl:template> </xsl:template>

</xsl:stylesheet></xsl:stylesheet>

A SAX invocation of A SAX invocation of startElementstartElement for for xsl:templatexsl:template would pass following parameters:would pass following parameters:

– namespaceURI= namespaceURI= http://www.w3.org/1999/XSL/Transformhttp://www.w3.org/1999/XSL/Transform

– localname = localname = template, template, qName =qName = xsl:template xsl:template


Namespaces: Example (2)Namespaces: Example (2)

<xsl:stylesheet version="1.0" ... <xsl:stylesheet version="1.0" ... xmlns="http://www.w3.org/TR/xhtml1/strict"> xmlns="http://www.w3.org/TR/xhtml1/strict"> <xsl:template match="/"> <xsl:template match="/"> <html> ... </html> <html> ... </html> </xsl:template> </xsl:template>

</xsl:stylesheet></xsl:stylesheet>

A SAX invocation of A SAX invocation of startElementstartElement for for htmlhtml would give would give

– namespaceURI=namespaceURI=http://www.w3.org/TR/xhtml1/stricthttp://www.w3.org/TR/xhtml1/strict(as default namespace for element names without a (as default namespace for element names without a

prefix),prefix), localname = localname = html, html, qName =qName = html html


ContentHandlerContentHandler interface (cont.) interface (cont.)

characters(char ch[], characters(char ch[], int start, int length) int start, int length)

– notification of character data. notification of character data. ignorableWhitespace(char ch[], ignorableWhitespace(char ch[],

int start, int length)int start, int length)– notification of ignorable whitespace in element content. notification of ignorable whitespace in element content.

<!DOCTYPE A [<!ELEMENT A (B)> <!DOCTYPE A [<!ELEMENT A (B)> <!ELEMENT B (#PCDATA)> ]> <!ELEMENT B (#PCDATA)> ]>

<A><A><B> <B> </B></B>

</A> </A>

Ignorable whitespaceIgnorable whitespace

Text contentText content


SAX Processing Example (1)SAX Processing Example (1)

InputInput: XML representation of a personnel database:: XML representation of a personnel database:

<?xml version="1.0" encoding="ISO-8859-1"?><?xml version="1.0" encoding="ISO-8859-1"?>

<db><db><person idnum="1234"><person idnum="1234"><last>Kilpeläinen</last><first>Pekka</first></person><last>Kilpeläinen</last><first>Pekka</first></person>

<person idnum="5678"><person idnum="5678">

<last>Möttönen</last><first>Matti</first></person><last>Möttönen</last><first>Matti</first></person>

<person idnum="9012"><person idnum="9012"><last>Möttönen</last><first>Maija</first></person><last>Möttönen</last><first>Maija</first></person>

<person idnum="3456"><person idnum="3456"><last>Römppänen</last><first>Maija</first></person><last>Römppänen</last><first>Maija</first></person>

</db></db>



TaskTask: Format the document as a list like this:: Format the document as a list like this:

Pekka Kilpeläinen (1234)Pekka Kilpeläinen (1234)Matti Möttönen (5678)Matti Möttönen (5678)Maija Möttönen (9012)Maija Möttönen (9012)Maija Römppänen (3456)Maija Römppänen (3456)

Solution strategy using event-based processing:Solution strategy using event-based processing:– at the start of a at the start of a personperson, record the , record the idnum idnum (e.g.,(e.g., 1234)1234)– keep track of starts and ends of elements keep track of starts and ends of elements lastlast and and first, first,

in order to record content of those elements (e.g., in order to record content of those elements (e.g., "Kilpeläinen" and "Pekka")"Kilpeläinen" and "Pekka")

– at the end of each at the end of each personperson, output the collected data, output the collected data



ApplicationApplication: Begin by importing relevant classes:: Begin by importing relevant classes:

import org.xml.sax.XMLReader;import org.xml.sax.XMLReader;import org.xml.sax.Attributes;import org.xml.sax.Attributes;import org.xml.sax.ContentHandler;import org.xml.sax.ContentHandler;

//Default (no-op) implementation of//Default (no-op) implementation of//interface ContentHandler://interface ContentHandler:import org.xml.sax.helpers.DefaultHandler;import org.xml.sax.helpers.DefaultHandler;

// SUN JAXP used to obtain a SAX parser:// SUN JAXP used to obtain a SAX parser:import javax.xml.parsers.*;import javax.xml.parsers.*;



Define a class to implement relevant call-back Define a class to implement relevant call-back methods:methods:

public class SAXDBApp extends public class SAXDBApp extends DefaultHandlerDefaultHandler{{

// Flags to remember element context:// Flags to remember element context:

private boolean InFirst = false, private boolean InFirst = false, InLast = false; InLast = false;

// Storage for element contents and // Storage for element contents and

// attribute values:// attribute values:

private String FirstName, LastName, IdNum;private String FirstName, LastName, IdNum;



Call-back methods:Call-back methods:– record the start of record the start of firstfirst and and last last elements, elements,

and the and the idnumidnum attribute of a attribute of a personperson::public void public void startElementstartElement ( (

String namespaceURI, String localName,String namespaceURI, String localName, String rawName, Attributes atts) { String rawName, Attributes atts) {

if (localName.equals("first")) if (localName.equals("first")) InFirst = true;InFirst = true;

if (localName.equals("last")) if (localName.equals("last")) InLast = true;InLast = true;

if (localName.equals("person")) if (localName.equals("person")) IdNum = atts.IdNum = atts.getValuegetValue("idnum");("idnum");

} // startElement} // startElement



Call-back methods continue:Call-back methods continue:– Record the text content of elements Record the text content of elements firstfirst and and last last

in corresponding variables:in corresponding variables:

public void public void characterscharacters ( (char ch[], int start, int length) {char ch[], int start, int length) {

if (InFirst) FirstName = if (InFirst) FirstName = new String(ch, start, length);new String(ch, start, length);

if (InLast) LastName = if (InLast) LastName = new String(ch, start, length);new String(ch, start, length);

} // characters } // characters



Call-back methods continue:Call-back methods continue:– at an exit from at an exit from personperson, output the collected data:, output the collected data:

public void public void endElementendElement(String namespaceURI, (String namespaceURI, String localName, String qName) {String localName, String qName) {

if (localName.equals("person")) if (localName.equals("person"))

System.out.println(FirstName + " " + System.out.println(FirstName + " " + LastName + " (" + IdNum + ")" );LastName + " (" + IdNum + ")" );

//Update the context flags://Update the context flags:

if (localName.equals("first")) if (localName.equals("first"))

InFirst = false; InFirst = false;

//(Correspondingly for "last" and InLast)//(Correspondingly for "last" and InLast)



Application Application mainmain method: method:

public static void main (String args[]) public static void main (String args[])

throws Exception {throws Exception {

// Instantiate an XMLReader (from JAXP // Instantiate an XMLReader (from JAXP

// SAXParserFactory):// SAXParserFactory):

SAXParserFactory spf =SAXParserFactory spf =SAXParserFactory.newInstance();SAXParserFactory.newInstance();

try {try {

SAXParser saxParser = spf.newSAXParser();SAXParser saxParser = spf.newSAXParser();

XMLReader xmlReader =XMLReader xmlReader =saxParser.getXMLReader();saxParser.getXMLReader();



MainMain method continues: method continues:// Instantiate and pass a new // Instantiate and pass a new // ContentHandler to xmlReader:// ContentHandler to xmlReader:

ContentHandlerContentHandler handler = new SAXDBApp(); handler = new SAXDBApp(); xmlReader.setContentHandler(handler);xmlReader.setContentHandler(handler); for (int i = 0; i < args.length; i++) {for (int i = 0; i < args.length; i++) { xmlReader.parse(args[i]);xmlReader.parse(args[i]); }}

} catch (Exception e) {} catch (Exception e) {System.err.println(e.getMessage());System.err.println(e.getMessage());

System.exit(1);System.exit(1);};};

} // main} // main

sdpl 2002notes 3: xml processor interfaces1 3. xml processor apis n how can applications manipulate...

Documents

xml processor interfaces3

xml processor interfacestasks

xml processor interfacessax

xml processor apishow

xml processor interfacesevent

xml parserscould

xml processingnotes

major xml