Download - Feb 2001C.Watters1 Grammars, SGML, & XML Agreeing on the rules

Feb 2001 C.Watters 1

Grammars, SGML, & XML

Agreeing on the rules


Overview

What is a grammarBNF notationRegular expressionsContext free grammars (remember Chomsky)SGMLHTMLXML (finally) and the DTD


What is a Grammar?

A grammar is a set of rules which can generate a construct from a list of

terminals determine if a construct obeys the rules

(i.e. is well formed)

Example - English construct is a sentence terminals are words


Syntax not Semantics

Let’s expand definition of noun terminals Noun::=(car | hat | TV) no problem with syntax! Hat running a little vague.

They are flying planes. No problem with syntax. Semantics not so clear


What is a grammar for anyway?

1. Parse Input Examines input and determines if it satisfies

the rules of a given grammar Joe Mary. If(a<3){jump} <html>my page</hjkl>

2. Generate output Use the rules to generate well-formed

entities Joe runs. If(a < 3){b=a} <html>my page </html>


BNFBackus Naur (or Normal) Form

Notation for describing syntax of a languageJohn Backus and Peter Naur, 1960’s for ALGOLMeta-symbols used ::= LHS is defined by RHS | or < > category name (defined somewhere

else)Example <program>::= begin <statements>

end;


Useful extensions to BNF

Optional [else <statements>]repetitive items {<letter> | <digit> }recursion is allowed <integer> ::= <digit> | <integer>

<digit>

brackets for grouping <letter>(<digit> | <letter> <digit>)


Regular Expressions

Simple way to express languages or stringseg. One ‘a’ followed by (one ‘n’ followed by one ‘d’) or by one ‘t’

a((n d) | t)

note: may use + instead of |


Regular Expressions include

Concatenation\sequence A BSelection A|BKleene Closure (0 or more) A*Positive Closure(1 or more) A+

Bounded Repetition (1 to i) Ai

eg. A(n*| t) = {A, An, Ann, …, At}


Context-Free Grammars

CFG is a set of recursive productions used to generate patterns of strings satisfying the construct of the language

SGML and its subsets, HTML and XML are context-free grammars!CFG are more powerful than Regular Expressions


SGML

Standardized General Markup LanguageDeveloped by a committee!Led by Charles Goldfarb, 1978-1986a grammar to define the structure of documents

rules define the construct or structureterminals are <tags> and strings


XML

DTDsHow to use itExamples


DTD - grammar definition for a document type

Defines: element types (structure) attributes (terminals) constraints on combinations of these


Element Type Declaration<!DOCTYPE GarageSale [<!ELEMENT GarageSale (Date, Place, Notes)><!ELEMENT Date (#PCDATA)><!ELEMENT Place (#PCDATA)><!ELEMENT Notes (#PCDATA)> ]>

<GarageSale><Date>today</Date><Place>myhouse</Place><Notes>Rain or

shine</Notes> </GarageSale>


Sub-Elements<!ELEMENT Figure (Graphic|Code)>

<!ELEMENT Figure (Caption, (Graphic|Code))><!ELEMENT Figure (Caption?, (Graphic|Code))>

? Means optional

<!ELEMENT FTNOTE (P+)> 1 or more

<!ELEMENT FTNOTE (P*)> 0 or more

where Graphic etc are also defined as ELEMENTS


AttributesLet you add extra information to elements<!ELEMENT Place (#PCDATA)><!ATTLIST Place Address CDATA Email CDATA Phone CDATA><Place Address=“1234 Oak”>

<!ATTLIST SHIRT Size (small|medium|large)><Shirt size=“small”>

CDATA=> character data


Validating Parser

A DTD (document type definition) defines the grammar of a type of document

memo web page book

Validating Parser uses a DTDto check if a given document satisfies the rules of that grammar


HTML & XMLHTML is a subset of SGML with a

shared DTD HTMLDOC::=(<html> HEAD BODY

</html>)

XML is a subset of SGML with many DTD’s allowed

“XML is like HTML with the training wheels off” -Dan Connolly, leader of XML activity at W3C


XMLUses tags to identify semantics of data

looks like HTML, but isn’t<slide><title>Introduction</title> <author><first>Carolyn</first>

<last>Watters</last> </author>

<content>XML this and that</content></slide>

is license free, platform-independent and well-supported


HTMLHypertext Markup Language

Hypertext Markup Language

Presents documents via WWW browsers

Document layout and hyperlink specifications

Predefined set of tags (ie. Common DTD)


<HTML><TITLE>Statistics Canada</TITLE><BODY><H3>Welcome to Stats Canada</H3>Statistics Canada ……. . <p> We like numbers…..<img src=“mapleleaf.gif><ul>What we do<li><a href=“census.html”>Census</a><li><a href=“special.html”>Special surveys</a><li>a href=“online.html”>Online data</a></ul></BODY></HTML>


HTML

HTML - Advantages

Simple - fixed set of tags

Portable - used with all browsers

Linking - within and to external documents

HTML - Disadvantages

Limited tag set

Can’t separate the definition from content

Can’t define structure of contents


XML

XML allows anyone to define a document structure separate from its display structure

Explicit Definition - DTD

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Some CodeSome Code

Schema

Entity Passport Details

SubEntities Last Name First Name Address

Entity Address

SubEntities Street City Town State Province ……..


<!ELEMENT passport_details (last_name,first_name+,address)><!ELEMENT last_name (#PCDATA)><!ELEMENT first_name (#PCDATA)><!ELEMENT address (street,(city|town),(state|province),(ZIP|

postal_code),country,contact_no?,email*)><!ELEMENT street (#PCDATA)><!ELEMENT city (#PCDATA)><!ELEMENT town (#PCDATA)><!ELEMENT state (#PCDATA)><!ELEMENT province (#PCDATA)><!ELEMENT ZIP (#PCDATA)><!ELEMENT postal_code (#PCDATA)><!ELEMENT country (#PCDATA)><!ELEMENT phone_home (#PCDATA)><!ELEMENT email (#PCDATA)>

DTD

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Internal DTD and InstanceInternal DTD and Instance

<?xml version='1.0'?><!DOCTYPE passport_details [<!ELEMENT passport_details

(last_name,first_name+,address)><!ELEMENT last_name (#PCDATA)><!ELEMENT first_name (#PCDATA)><!ELEMENT address (street,(city|town),

(state|province),(ZIP|

postal_code),country,contact_no?,email*)>

<!ELEMENT street (#PCDATA)><!ELEMENT city (#PCDATA)><!ELEMENT town (#PCDATA)><!ELEMENT state (#PCDATA)><!ELEMENT province (#PCDATA)><!ELEMENT ZIP (#PCDATA)><!ELEMENT postal_code (#PCDATA)><!ELEMENT country (#PCDATA)><!ELEMENT phone_home (#PCDATA)><!ELEMENT email (#PCDATA)>]>

<passport_details><last_name>Smith</last_name><first_name>Jo</first_name><first_name>Stephen</first_name><address>

<street>1 Great Street</street>

<city>GreatCity</city><state>GreatState</state><postal_code>1234</

postal_code><country>GreatLand</

country>

<email>[email protected]</email></address>

</passport_details>

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Shared DTDShared DTD

XML Document specifies the DTD<?xml version='1.0'?>

<!DOCTYPE passport_details SYSTEM "PassportExt.dtd">

<passport_details><last_name>Smith</last_name><first_name>Jo</first_name><first_name>Stephen</first_name><address>

<street>1 Great Street</street><city>GreatCity</city><state>GreatState</state><postal_code>1234</postal_code><country>GreatLand</country>

<email>[email protected]</email></address>

</passport_details>


Coordinating Heterogenous Databases

Separation of Structure / Content / Display

Document Validity Checking

Potential Use in Standards

Importance of XML


Example

Boeing

Boeing places a DTD on its site

part purchasers use this DTD

Boeing can use multiple XSL stylesheets


Boeing (cont’d)

customer creates an order document, they can verify the validity of that document against the DTD.

this ensures they are transmitting only type-valid orders.

in turn, Boeing can ensure they are receiving only type-valid documents.


2. Using XML: DOM & SAX

DOM: Document Object Model

The DOM is a standard object application programming interface that gives developers programmatic control of XML document content, structure, formats, and more.

DOM defines a programmatic API for accessing XML documents.


3. Using XML: presenting data

Need to convert XML tags into appropriate HTML tags for use in a browser!!

<lastname>Smith</lastname>

<b>Smith</b> Smith


Stylesheets are used to present XML: The Cascading Stylesheet Specification (CSS)

The Extensible Style Language (XSL)

CSS XSL

Can be used with HTML? Yes No

Can be used with XML? Yes Yes

Transformation language? No Yes

Syntax CSS XML


CSS and XSL

CSS - Cascading Style Sheets can predefined HTML display (font etc) these are shared and reused

XSL - XML Style language predefine display characteristics for XML

entities transform into CSS for browsers to use

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Cascading Style SheetsCascading Style Sheets

CSSlast_name

{font-family: verdana, arial;font-size: 15pt;font-weight:bold;display: block;margin-bottom: 5pt;

}first_name

{font-family: verdana, arial;font-size: 15pt;font-weight:bold;display: block;margin-bottom: 5pt;

}

street, city, town, state, province, ZIP, postal_code{font-family: verdana, arial;font-size: 12pt;font-weight:bold;color:green;display:block;margin-bottom: 20pt;margin-top: 40pt;

}email

{font-family: verdana, arial;font-size: 12pt;font-weight:bold;color:blue;display:block;margin-top: 5pt;

}


CSS

Most local definition has precidenceMay be referred to (shared)

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<?xml version='1.0'?><xsl:stylesheet

xmlns:xsl="http://www.w3.org/TR/WD-xsl"xmlns="http://www.w3.org/TR/REC-html40"result-ns="">

<xsl:template><xsl:apply-templates/></xsl:template><xsl:template match="/"> <html>

<head><title><xsl:value-of select="/passport/last_name"/></title></head><body> <H1><xsl:value-of select="/pastport/last_name, first_name"/></H1> <H2>Address</H2>

<BLOCKQUOTE><xsl:apply-templates select="/passport/address"/></BLOCKQUOTE>

</body> </html>

XSL (Style Language)


Understanding A Template

Most templates have the following form:<xsl:template match="para"> <p><xsl:apply-templates/></p> </xsl:template>

The whole <xsl:template> element is a template

The match pattern determines where this template applies

Literal result elements come from non-XSL namespace(s)

XSLT elements come from the XSL namespace


Options for displaying XML

XMLDocument

CSSStylesheet

CSSStylesheet

XSLStylesheet

XSLStylesheet

XML enabledWeb BroswerXML enabledWeb Broswer

XML DisplayEngine

XML DisplayEngine

XSLTransformation

spec

HTMLDocument

Web BroswerWeb BroswerXSL

Transformation


2. Using XML:How does browser read XML ?

XML parser: A tool for reading XML documents

Microsoft's Internet Explorer 4.0 was the first Web browser to implement XML

Netscape will support XML metadata in Communicator/Navigator 5.0 as a delivery component code-named Aurora.


Desktop

Middle - Tier

Storage

Display

Multiple view created from the XML-base data

Data Delivery,

Manipulation:XML exchanged over HTTP manipulated via the DOM

Data Integration

XML emitted or generated from multiple source

XML delivered to other applications or objects for further processing

HTML view #1(eg.

Purchasing Agent)

HTML view #2(eg.

Consumer)

Web ServerDB Access, Integration

Business Rules(eg. Purchase order)

Web ServerDB Access, Integration

Business Rules(eg. Purchase order)

Mainframe Database

XML

XML Architecture


4. Case Study

An example of XML Tree structure

A simply example: Portfolio.xml Portfolio.xsl

http://msdn.microsoft.com/xml/samples/review/review-xsl.xml

Feb 2001 C.Watters 44..

storystory

addressaddressbookstorebookstore

menumenu

bodybody

reviewreview

logologo

namename

phonephone

datedate

reviewerreviewer personperson

summarysummary personperson

booksbooks

office suppliesoffice supplies

..

Tree Structure of the example


In the major Web Browser products.

In Microsoft Office 2000.

In every major database tool by end of 2000.

In every HTML tool by end of 2000.

CommerceNet believes that XML may just be the “killer application” needed to open up the Worldwide Web for Electronic Commerce.

Is this for real?


XML - AdvantagesPlatform and system independentUser-defined tagsDoesn’t require explicit DTDDisplay format and content are separate

XML - DisadvantagesRequires a processing application“Pickier” than HTMLMust be converted to HTML to view in browser

Summary


W3 Consortium: www.w3.com

kazillions of XML books in every bookstore!

Resources


6. Reference

Jon Bosak and Tim Bray, Scientific American, May 1999 [http://www.sciam.com/1999/0599issue/0599bosak.html]

Norman Walsh: What is XML? Oct. 3, 1998 [http://xml.com/xml/pub/98/10/guide1.html#AEN58]

Graphic Communications Association web site [http://www.gca.org/whats_xml/default.htm]

University College Cork [http://www.ucc.ie/xml/]

Microsoft MSDN online samples [http://msdn.microsoft.com/xml/samples/review/review-xsl.xml]

[http://www.oasis-open.org/cover/xsl.html]

Charles F. Goldfarb, Paul Prescod, The XML Handbook, 1998

Download - Feb 2001C.Watters1 Grammars, SGML, & XML Agreeing on the rules

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