Applications of CFG

1
Applications of CFG

• Parser and parser generator
• Markup languages.

2
Grammar and XML

• XML Basics
• History
• Syntax
• Well-formed XML
• Valid XML
• Parsing XML

3
What is XML (eXtremely Marketed Language)
What is XML (eXtensible Markup Language)

• Markup
• A sequence of characters inserted into a text
  file, to indicate how the file should be
  displayed, or to describe the logical structure.
• Markup is everything in a document that is not
  content.
• Initially used in typesetting a document

4
What is XML (eXtensible Markup Language)

• Markup in XML
• Markup indicators are called tags. e.g.
• ltfont colorbluegt
• A pair of tags and the things enclosed in tags is
  called element. e.g
• ltfont colorbluegt formatted as blue lt/fontgt

5
What is XML (eXtensible Markup Language) (cont.)

• Extensible
• In general Something that is designed that users
  or later designers can extend its capability.
• In XML Allow you to define your own tags to
  describe data
• You can represent any information
• You can represent in the way you want
• XML is a meta-language
• A language to define other languages
• Use DTD to define the syntax of a language

6
Markup (and extensible) languages are not new

• SGML (Standard Generalized Markup Language)
• Markup, extensible
• 1980 first publication, 1986 ISO standard
• HTML(HyperText Markup Language)
• Markup, hypertext, Subset of SGML
• Started 1990, CERN (Centre Européen de Recherche
  Nucléaire, or European High-Energy Particle
  Physics lab)
• XML (eXtensible Markup Language)
• Subset of SGML
• Started 1996, adopted by W3C 1998
• Eliminate the complexity of SGML
• Separate the data from the formatting information
  in HTML

SGML
HTML
7
HTML

• table lttablegt
• Table head ltTHgt
• Table row ltTRgt
• Table data ltTDgt

open tag, element name
Attribute value
attribute

• lthtmlgtltbodygt  Stock table
• ltTABLE border"1"gt
• ltTRgtltTHgt Exchange lt/THgt ltTHgt Name lt/THgt
  ltTHgt Price lt/THgt lt/TRgt
• ltTRgtltTDgt nasdaq lt/TDgt ltTDgt amazon corp lt/TDgt
  ltTDgt 16.875 lt/TDgt lt/TRgt 
• ltTRgtltTDgt nyse lt/TDgt ltTDgt IBM inc lt/TDgt
  ltTDgt 102.250lt/TDgt lt/TRgt 
• lt/TABLEgt lt/bodygtlt/htmlgt

stock.html
closing tag
data
Displayed in browser
8
XML and HTML

• Similarities
• They are both markup languages
• They are both simple.
• Differences

9
XML Example
attribute

• lt?xml version"1.0" ?gt
• ltstocksgt
• ltstock exchange"nasdaq"gt 
• ltnamegtamazon corplt/namegt  
• ltsymbolgtamznlt/symbolgt  
• ltpricegt16lt/pricegt  
• lt/stockgt
• ltstock exchange"nyse"gt 
• ltnamegtIBM inclt/namegt  
• ltpricegt102lt/pricegt  
• lt/stockgt 
• lt/stocksgt

element
stock.xml

• An XML document has a group of elements
• Each element has an opening tag and a closing
  tag
• An element can have attributes.

10
Well formed XML Document

• An XML document is well formed if it conforms to
  XML syntax rules.
• Additional rules
• XML document must have a root element
• Attribute values must be quoted
• XML is case sensitive
• Try to find bugs in the following XML document

lt?xml version"1.0" ?gt ltstock
exchange"nasdaq"gt  ltnamegtamazon corp
lt/namegt   ltsymbolgtamznlt/symbolgt  
ltpricegt16lt/pricegt   lt/stockgt ltstock
exchange nyse gt  ltnamegtIBM inclt/namegt  
ltpricegt 102 lt/PRICEgt   lt/stockgt 
ltstocksgt
lt/stocksgt
11
Valid XML document
lt?xml version"1.0" ?gt ltstocksgt ltnamegt
ltstockgt 102lt/stockgt   lt/namegt ltpricegtIBM
inclt/pricegt   ltsymbolgtamzn lt/symbolgt  
ltpricegt16lt/pricegt   ltstock exchange"nyse"gt 
ltpricegt amazon lt/pricegt   lt/stockgt 
lt/stocksgt

• Problem
• Not every well formed document makes sense
• Solution
• Associate XML with a DTD or XML Schema
• Valid XML document conforms to the DTD or XML
  Schema.

12
XML DTD (Document Type Definition)

• What DTD is a set of rules to define the syntax
  of a language. It is similar to context free
  grammar.
• Why Help XML generation and processing.
• How Write a sequence of element declarations and
  attribute declarations.
• Element declaration
• lt!ELEMENT tagName tagContentgt
• Attribute declaration
• lt!ATTLIST tagName attName attContentgt

Repeat 0 or more times
Occur 0 or once.
lt!ELEMENT stocks (stock)gt lt!ELEMENT stock (name,
symbol?, price)gt lt!ATTLIST stock exchange CDATA
gt lt!ELEMENT name (PCDATA)gt lt!ELEMENT symbol
(PCDATA)gt lt!ELEMENT price (PCDATA)gt
stock.dtd
13
DTD and Context Free Grammar

• DTD is similar to Context Free Grammar
• lt!ELEMENT stocks (stock)gt
• stocks? e stock stocks
• lt!ELEMENT stock (name, symbol?, price)gt
• stock ? name price name symbol price
• DTD makes the language extensible

14
Grammar and XML

• XML Basics
• History
• Syntax
• Well-formed XML
• Valid XML
• Parsing XML

15
DOM (Document Object Model)

• What DOM is application programming interface
  (API) for processing XML documents
• http//www.w3c.org/DOM/
• Why unique interface. platform and language
  independent
• How It defines the logical structure of
  documents and the way to access and manipulate it
• With the Document Object Model, one can
• Create an object tree
• Navigate its structure
• Access, add, modify, or delete elements etc

16
XML tree hierarchy

• XML can be described by a tree hierarchy

Document
Unit
Document
Sub-unit
Parent
Unit
Child
Sub-unit
Sibling
17
DOM tree model

• Generic tree model
• Node
• Type, name, value
• Attributes
• Parent node
• Previous, next sibling nodes
• First, last child nodes
• Many other entities extends node
• Document
• Element
• Attribute
• ... ...

18
DOM class hierarchy
DocumentFragment
Document
Text
CDATASection
CharacterData
Comment
Attr
Node
Element
DocumentType
NodeList
Notation
NamedNodeMap
Entity
DocumentType
EntityReference
ProcessingInstruction
19
JavaDoc of DOM API
http//xml.apache.org/xerces-j/apiDocs/index.html
20
A few words about javadoc

• javadoc is a command included in JDK
• It is a useful tool generate HTML description for
  your programs, so that you can use a browser to
  look at the description of the classes
• JavaDoc describes classes, their relationships,
  methods, attributes, and comments.
• When you write java programs, the JavaDoc is the
  first place that you should look at
• For core java, there is JavaDoc to describe every
  class in the language
• To learn how to use regex, look at
  javax.util.regex package
• To learn how to write a string to a file, look at
  the File class in javaDoc
• To know how to use DOM, look at the javaDoc of
  org.w3c.dom package.
• If you are a serious java programmer
• you should have the core jdk javaDoc ready on
  your hard disk
• You should generate the javaDoc for other people
  to look at.
• To run javadoc, type
• Dgtjavadoc .java
• This is to generate JavaDoc for all the classes
  under current directory.

21
Some important DOM interfaces

• The DOM defines several Java interfaces
• Node The base data type of the DOM
• Element Represents element
• Attr Represents an attribute of an element
• Text The content of an element or attribute
• Document Represents the entire XML document. A
  Document object is often referred to as a DOM
  tree

22
Methods in Node interface

• Three categories of methods
• Node characteristics
• name, type, value
• Contextual location and access to relatives
• parents, siblings, children, ancestors,
  descendants
• Node modification
• Edit, delete, re-arrange child nodes

23
XML parser and DOM
DOM XML parser
Your XML application
DOM API
DOM Tree

• When you parse an XML document with a DOM parser,
  you get back a tree structure that contains all
  of the elements of your document
• DOM also provides a variety of functions you can
  use to examine the contents and structure of the
  document.

24
DOM tree and DOM classes
there are more nodes. refer slide 28.
ltstocksgt
ltstock Exchangenyse gt
ltstock exchangenasdaqgt
ltnamegt
ltpricegt
ltnamegt
ltpricegt
ltsymbolgt
IBM
105
amzn
15.45
Amazon inc
Element
child
25
Use Java to process XML

• Tasks
• How to construct the DOM tree from an XML text
  file?
• How to get the list of stock elements?
• How to get the attribute value of the second
  stock element?
• Construct the Document object
• Need to use an XML parser (XML4J)
• remember to import the necessary packages
• The benefits of DOM the following lines are the
  only difference if you use another DOM XML parser.

26
Get the first stock element
lt?xml version"1.0" ?gt ltstocksgt ltstock
exchange"nasdaq"gt  ltnamegtamazon corplt/namegt
  ltsymbolgtamznlt/symbolgt  
ltpricegt16lt/pricegt   lt/stockgt ltstock
exchange"nyse"gt  ltnamegtIBM inclt/namegt  
ltpricegt102lt/pricegt   lt/stockgt  lt/stocksgt
27
Navigate to the next sibling of the first stock
element
lt?xml version"1.0" ?gt ltstocksgt ltstock
exchange"nasdaq"gt  ltnamegtamazon corplt/namegt
  ltsymbolgtamznlt/symbolgt  
ltpricegt16lt/pricegt   lt/stockgt ltstock
exchange"nyse"gt  ltnamegtIBM inclt/namegt  
ltpricegt102lt/pricegt   lt/stockgt  lt/stocksgt
28
Be aware the Text object in two elements
lt?xml version"1.0" ?gt ltstocksgt ltstock
exchange"nasdaq"gt  ltnamegtamazon corplt/namegt
  ltsymbolgtamznlt/symbolgt  
ltpricegt16lt/pricegt   lt/stockgt ltstock
exchange"nyse"gt  ltnamegtIBM inclt/namegt  
ltpricegt102lt/pricegt   lt/stockgt  lt/stocksgt
Question How many children does the stocks node
have?
text
text
text
text
text
text
text
text
text
text