02 - XML - Fundamentals

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eXtensible Markup LanguageLectu rer : Phan Vo Minh Than g MSc.

eXtensible Markup Language

Fundamentals

eXtensible Markup Language Phan Vo Minh Thang


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XML Lectures Notes XML Fundamentals


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< e s o 0 > < ate a > ectu es otes u da e ta s

Attributes

Attach additional information to elements An attribute is a name-value pair attached to an elements

start-tag

One element can have more than one attribute

Name and value are separated by = and optional whitespace

Attribute value is enclosed in double or single quotation marks

03-5712121

Attribute order is not significant

Example 2-4

Alan Turing


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Attributes and Elements

When and whether one should use child elements orattributes to hold information?

Attributes are for metadata about the element, while elements arefor the information itself

Each element may have no more than one attribute with agiven name

The value of attribute is simply a text string limited instructure

An element-based structure is a lot more flexible and

extensible If you are designing your own XML vocabulary, it is up to

you to decide when to use which


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XML Names

Rules for naming elements, attributes May contain essentially any alphanumeric character

and non-english letters, numbers, and ideograms

May contain underscore(_), period (.), and hyphen (-)

XML may not contain whitespace of any kind

All names beginning with the string xml (in anycombination of case) are reserved for standardization inW3C XML-related specifications

Start with either letters. ideograms and underscore (_)

No limit to the name length


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XML Names (Cont.)

HTML elements in XML are always in uppercase XML elements are frequently written in lowercase

When a name consists of several words, the words are usually

separated by a hyphen (-)

address-book

OR

The first letter of each word in XML elements are frequently inuppercase and no separation character

AddressBook


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Element names example

Which tags are named correctly?


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Entity References

What if the character data inside an element contains < ? Entity reference when an application parses an XML

document, it replaces the entity reference with the actual

characters to which the entity reference refers Entity references are markups

XML predefines 5 entity references you can define more

the greater-than sign

" the straight, double quotation marks (")

' the straight single quote (')


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CDATA Sections

What if your character data have a lot of


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Comments

XML documents can be commented so that coauthors canleave notes for each other and themselves

Begin with

The double hyphen -- should not appear anywhere inside thecomment until the closing -->

Comments may appear anywhere in the character data ofa document

Comments may appear before or after the root element

Comments may not appear inside a tag or inside another

comment Comments are strictly for making the raw source code of

an XML document more legible to human readers


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The XML Declaration

XML documents should (but not have to) begin with anXML declaration

The XML declaration must be the first thing in the document

It must not be preceded by any comments, whitespace

An XML declaration specifies encoding and standalone

Encoding: specify the character set used in the XML document

Default to Unicode/UTF8

Standalone: if the value is "no", then an application may berequired to read an external DTD to determine the proper valuesfor parts of the document


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Rules for Well-Formed XML

Rule 1: Mandatory closing tags The set of tags is unlimited but all container tags must have end

tags

Example of legal XML Phan Minh Vo Thang

Associate Professor 25

Rule 2: There must be exactly one root element


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Rules for Well-Formed XML (Cont.)

Rule 3: Proper element nesting All tags must be nested correctly. Like HTML, XML can intermix

tags and text, but tags may not overlap each other.

Legal XML Hao-Ren Ke is an

pioneerforComputerized Interlibrary Loanin Taiwan

Illegal XML

ClavenXML provides a data bus


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Rules for Well-Formed XML (Cont.)

Rule 4: Attribute values must be single or double quoted Legal

Illegal

Rule 5: An element may not have two attributes with thesame name

Rule 6: Comments and processing instructions may not

appear inside tags Rule 7: No unescaped < or & signs may occur in the

character data of an element or attributes


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Rules for Well-Formed XML

Rule 8: Empty elements must be written in an abbreviatedform using special XML syntax.

Legal

is equivalent to

Illegal


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Four Common Errors

Forget End Tags Forget that XML is Case Sensitive

Introduce Spaces in the Name of Element

Forget the Quotes for Attribute Value


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Exercise

Is it a well-formed XML document?

The XML Handbook

Prentice Hall PTR

Charles F. Goldfarb

XML Basics

Carolyn Strong

April 17


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Well-formed checking using tools


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Info

Course name:

Special Selected Topic in

Information System Section: XML Fundamentals

Number of slides: 26

Updated date: 12/02/2006 Contact: Mr.Phan Vo Minh Thang

([email protected])

02 - XML - Fundamentals

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