Markup Languages & XML - BY VISHAL KAMTAM VENKATESH

What are markup languages??  Language that uses tags to define elements within a document.  It is human-readable.  The two most popular markup languages are HTML and XML.

What is HTML?  HTML-Hyper text Markup Language.  HTML is comprised of “elements” and “tags”  Begins with and ends with  Elements (tags) are nested one inside another: Tags have attributes:  HTML describes structure using two main sections: and

Example HTML code: Hello World Hello World

Output:

How they work?

Representation of HTML as Parse Tree Hello World

Representation in CFG  HTML can be described by classes of text  Text is any string of characters literally interpreted (i.e. there are no tags, user-text)  Char is any single character legal in HTML tags.Blanks included  Element is  Text or  A pair of matching tags and the document between them, or  Unmatched tag followed by a document  Doc is sequences of elements  ListItem is the tag followed by a document followed by  List is a sequence of zero or more list items

HTML Grammar Char a | A | … Text ε | Char Text Doc ε | Element Doc Element Text | Doc | Doc | List ListItem Doc List ε | ListItem | List

HTML Example popular markup languages HTML XML The text can be viewed as : popular markup languages 1. HTML 2. XML

Extensible Mark-up languages (XML)

 XML has user defined tags whereas HTML has predefined tags.  designed to describe data, not to display data. eg: ” 12 Maple Street ” 12 Maple Street  In most web applications, XML is used to describe data, while HTML is used to format and display the data.

Example XML Mary likes John.

PARSE TREE

PRODUCTION RULES → → Mary|John → believes → likes

XML’s DTD  The DTD lets us define our own grammar  Context-free grammar notation, also using regular expressions  Form of DTD:  Element definition:

Element Description  Element descriptions are regular expressions  Basis  Other element names  #PCDATA, for any TEXT without tags  Operators  | for union , for concatenation  * zero or more occurrences of  ? for zero or one occurrence of  + for one or more occurrences of

Example DTD-1 <!DOCTYPE PcSpecifications [ ]>

Pc Specs XML Document 4560 $2295 Intel Pentium 4Ghz 8192 Maxtor Diamond 2000Gb 32x …..

DTD and Production Rules  DTD: Production Rule: PROCESSOR  MANF MODEL SPEED  DTD: <!ELEMENT DISK (HARDDISK|CD|DVD) Production Rule: Disk  HARDDISK|CD|DVD  DTD:

 Production Rule: PC  AB A  Model Price Processor Ram B  Disk+  Last production is illegal.we introduce C B  CB|C C  Disk  We can rewrite above expression PC  Model Price Processor Ram B B  Disk B|Disk

Example DTD-2  <!DOCTYPE SENTENCES [ }>

Production Rules (SENTENCE)  (NOUN-PHRASE)(VERB-PHRASE) (NOUN-PHRASE)  (CMPLX-NOUN)|(CMPLX-NOUN)(PREP-PHRASE) (VERB-PHRASE)  (CMPLX-VERB)|(CMPLX-VERB)(PREP-PHRASE) (PREP-PHRASE)  (PREP)(CMPLX-NOUN) (CMPLX-NOUN)  (ARTICLE)(NOUN) (ARTICLE)  A|THE (NOUN)  BOY|GIRL|FLOWER (VERB)  TOUCHES|LIKES|SEES (PREP)  WITH

CONCLUSION  DTD for both XML and CFG describe languages with certain rules and restrictions, and thereby declare what’s legal and what’s not in a given language.  An XML document is considered valid if it’s well formed and has been validated against a DTD.  A string is a valid string in a given Context-free language if the Context-free grammar for that language can generate it.

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