XML Parsers

XML Parsers

Kanda Runapongsa ([email protected])

Dept. of Computer EngineeringKhon Kaen University

mailto:[email protected]

168493: XML and Web Services (II/2546)

2

What are XML Parsers? In order to process XML data,

every program or server process needs an XML parser

The parser extracts the actual data out of the textual representation

It is essential for the automatic processing of XML documents


3

What are XML Parsers? (Cont.)

Parsers also check whether documents conform to the XML standard and have a correct structure

There are two types of XML parsers Validating: check documents against a

DTD or an XML Schema Non-validating: do not check documents

against a DTD or an XML Schema.


4

Available XML Parsers MSXML: Microsoft XML Parser:

http://msdn.microsoft.com/xml/ Apache Xerces: XML parsers in Java and

C++: http://xml.apache.org IBM AlphaWorks:

http://www.alphaworks.ibm.com/tech/xml4j

expat: http://www.jclark.com/xml/expat.html

XP: http://www.jclark.com/xml/xp/ Other sources

XML.com web site Cover Pages: XML web site


5

SAX and DOM SAX (Simple API for XML) and DOM

(Document Object Model) allow programmers to access their information stored in XML documents Using any programming language and

a parser for that language Both of them take very different

approaches to giving you access to your information


6

What is DOM? DOM gives you access to the

information stored in your XML document as a hierarchical object model

DOM creates a tree of nodes (based on the structure and information in your XML document)

You can access your information by interacting with this tree of nodes


7

Hierarchical Structure


8

DOM Each element node actually

contains a list of other nodes as its children

These children might contain text values or other nodes

DOM preserves the sequence of the elements that it reads from XML documents


9

What is SAX? SAX chooses to give you access

to the information in your XML document, not as a tree of nodes, but as a sequence of events

SAX chooses not to create a default object model on top of your XML document (like DOM does)


10

SAX vs. DOM In the case of DOM, the parser

does almost everything Read the XML document in Create an Object model on top of it Give you a reference to this object

model (a Document object) so that you can manipulate it

SAX doesn’t expect the parser to do much


11

SAX vs. DOM (Cont.) For SAX, the parser should

Read in the XML document Fire a bunch of events depending

on what tags it encounters in the XML document

Then, the programmer needs to make sense of all the tag events and create objects in their own object model


12

SAX vs. DOM (Cont.) SAX can be really fast at runtime

if your object model is simple It is faster than DOM because it

bypasses the creation of a tree based object model of your information

On the other hand, you have to write a SAX document handler to interpret all the SAX events


13

SAX Events SAX events can be

An event for every open tag An event for every close tag An event for #PCDATA section An event for CDATA section

Your handlers have to interpret these events and make sense out of them


14

When to Use DOM DOM is quite easy to implement

Good for the development to be done in a short amount of time

DOM has crated a tree of nodes When you need to quickly access children

and parent of current nodes When you need to modify an XML

structure What are the disadvantages of using

DOM?


15

When to Use SAX SAX requires little memory because

It does not construct an internal representation of the XML data

It works well when you simply want to read data and have the application act on it You see the data as it streams in, but

you can’t go back to an earlier position or leap ahead to a different position

Documents

XML Parsers