Session02 XML Syntax

8/14/2019 Session02 XML Syntax

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2008 MindTree Consulting

XML Syntax

Rules of XML Language

Sep-2009


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Slide 2

Agenda

Need for XML

Quiz

XML Syntax - Rules of XML language


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2008 MindTree Consulting

Need For XMLRevision of previous session

Quiz


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Slide 5

XML

How can you have both more tags and fewer tags in a singlelanguage?

To resolve this dilemma, XML makes essentially two changes to HTML:

It predefines no tags.

It is stricter.


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Slide 6

What is Markup

In an electronic document, the markup is the codes, embeddedwith the document text, which store the information required for

electronic processing, like font name, boldness or, in the case of

XML, the document structure. This is not specific to XML. Every

electronic document standard uses some sort of markup.


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Applications of XML

PublishingXML is being used by an increasing number of publishers as the format

for documents.

Example XML document for a monthly newsletter. As you can see, it uses

elements for the title, abstract, paragraphs, and other concepts commonin publishing.

Business Document Exchange

For example placing the order in XML rather than on paper. Advantage is

that software can process it. An application could read this order andautomatically fulfill it.

RSS / Atom

Eg Bloglines


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XML Introduction - QuizBasic questions on XML Introduction


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XML Introduction - Quiz

XML stands forXML is about the description of data, and not its presentation.

XML allows us to define your own tags, so we can create our own

markup languages.

The XML specification is owned by W3C

XML is designed to be both machine readable and human readable.

XML provides a platform-neutral, language-independent means of

describing data.Obviously, its the markup that differentiates the XML document

from plain text.


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The XML SyntaxStart & End Tags, Elements, Element nesting XML Names, Attributes,

XML Declaration, Entities, CDATA, Comments, Processing Instructions,Well formed XML


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XML - Example

Listing 2.1: An Address Book in XML

John Doe

34 Fountain Square Plaza

OH45202

CincinnatiUS

513-555-8889

513-555-7098

JackSmith

513-555-3465


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Elements Start and End Tags

The building block of XML is the element, as thats what comprisesXML documents. Each element has a name and a content.

513-555-7098

The content of an element is delimited by special markups known

as start tag and end tag.

Unlike HTML, both start and end tags are required. The following is

not correct in XML:

513-555-7098


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Names in XML

Element names must follow certain rules. As we will see, there are othernames in XML that follow the same rules.

Names in XML must start with either a letter or the underscore character

(_). The rest of the name consists of letters, digits, the underscore

character, the dot (.), or a hyphen (-). Spaces are not allowed in

names.

Finally, names cannot start with the string xml, which is reserved for the

XML specification itself.

Unlike HTML, names are case sensitive in XML.

By convention, XML elements are frequently written in lowercase. When a

name consists of several words, the words are usually separated by a

hyphen, as in address-book or written as AddressBook. Choose the

convention that works best for you but try to be consistent.


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Names in XML - Quiz

The following are examples of valid or invalid element names inXML:


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Attributes

It is possible to attach additional information to elements in the form ofattributes.

Attributes have a name and a value. The names follow the same rules as

element names.

The syntax is similar to HTML. Elements can have one or more attributes in

the start tag, and the name is separated from the value by the equalcharacter.

The value of the attribute is enclosed in double or single quotation marks.

For example, the tel element can have a preferred attribute:

513-555-8889Unlike HTML, XML insists on the quotation marks. The XML processor would

reject the following:

513-555-8889


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Empty Element

Elements that have no content are known as empty elements.Usually, they are enclosed in the document for the value of their

attributes.

There is a shorthand notation for empty elements: The start and

end tags merge and the slash from the end tag is added at the endof the opening tag.

For XML, the following two elements are identical:

Quiz

An empty element tag can have attributes. ( Yes / no)


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Nesting of Elements

Element content is not limited to text; elements can contain otherelements that in turn can contain text or elements and so on.

An XML document is a tree of elements. There is no limit to the depth ofthe tree, and elements can repeat. As you see in Listing 2.1, there are twoentry elements in the address-book element. The entry for John Doe hastwo tel elements. Figure 2.1 is the tree of Listing 2.1. [Refer: XML Example

slide]An element that is enclosed in another element is called a child. The

element it is enclosed into is itsparent.

Jack

Smith

Start and end tags must always be balanced and children are alwayscompletely enclosed in their parents. Following is legal or illegal?

JackSmith


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Root

At the root of the document there must be one and only oneelement. In other words, all the elements in the document must be

the children of a single element.

Quiz: Following example is legal or illegal?

John Doe

JackSmith


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Slide 20

XML Declaration

TheXML declaration is the first line of the document. Thedeclaration identifies the document as an XML document. The

declaration also lists the version of XML used in the document.

The declaration can contain other attributes to support otherfeatures such as character set encoding.

The XML declaration is optional.

If the declaration is included however, it must start on the first

character of the first line of the document. The XMLrecommendation suggests you include the declaration in every XML

document.


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Slide 21

XML Declaration Stand-alone document

If an XML document can be read with no reference to external sources, it is said to

be a stand-alone document. Such documents can be annotated with a standaloneattribute with a value of yes in the XML declaration. If an XML document requiresexternal sources to be resolved to parse correctly and/or to construct the entiredata tree (for example, a document with references to external general entities),then it is not a stand-alone document. Such documents may be markedstandalone='no', but because this is the default, such an annotation rarely appears in

XML documents.XML declarations


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Slide 22

Comments

To insert comments in a document, enclose them between .

Comments are used for notes, indication of ownership, and more.

They are intended for the human reader and they are ignored by

the XML processor.

Comments cannot be inserted in the markup. They must appear

before or after the markup.


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Slide 23

Unicode

Characters in XML documents follow the Unicode standard.

XML uses the 16 bit Unicode character set.XML processor must recognize the UTF-8 and UTF-16 encodings.

Most processors support other encodings. In particular, for WesternEuropean languages, they support ISO 8859-1 (the official name for Latin-1).

Documents that use encoding other than UTF-8 or UTF-16 must start withan XML declaration. The declaration must have an attribute encoding toannounce the encoding used. For example, a document written in Latin-1(such as with Windows Notepad) could use the following declaration:

Jos Dupont


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Slide 24

XML Declaration - Quiz

How the XML processor can read the encoding parameter. Indeed,to reach the encoding parameter, the processor must read the

declaration. However, to read the declaration, the processor needs

to know which encoding is being used.

What about those documents that have no declaration (since thedeclaration is optional)?


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Slide 26

Predefined Entities in XML

XML predefines entities for the characters used in markup (angle brackets,

quotes, and so on). The entities are used to escape the characters from

element or attribute content. The entities are

< left angle bracket must be escaped with > in the combination ]]> inCDATA sections (see the following)

' single quote can be escaped with ' essentially in parameter

value

" double quote can be escaped with " essentially in parameter

valueQuiz Correct / Incorrect?

Mark & Spencer

Mark & Spencer


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Slide 27

Character references

XML also supports character references where a letter is replaced by its

Unicode character code.

DecimalUnicodeValue;

Character references that start with provide a decimal representation of the character

code.

HexadecimalUnicodeValue;

Character references that start with provides a hexadecimal representation of the

character code.

Example - Character references

Martin

Franais


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Slide 28

Processing Instructions

Processing instructions (abbreviated PI) is a mechanism to insertnon-XML statements, such as scripts, in the document.

The processing instruction is enclosed in .

The first name is the target. It identifies the application or the

device to which the instructions are directed. The rest of theprocessing instructions are in a format specific to the target. It

does not have to be XML.


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Slide 29

CDATA Sections

As you have seen, markup characters (left angle bracket and ampersand)that appear in the content of an element must be escaped with an entity.

For some applications, it is difficult to escape markup characters, if only

because there are too many of them. Also, it is difficult to include an XML

document in an XML document.

CDATA (Character DATA) sections are intended for these cases. CDATA

sections are delimited by . The XML processor ignores

all markup except for]]>

PCDATA stands for parsed character data and means the element can

contain text. #PCDATA is often (but not always) used for leaf elements.The difference between CDATA and PCDATA is that PCDATA cannot contain

markup characters.


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Slide 31

CDATA Section - Example

The following example uses a CDATA section to insert an XMLexample into an XML document:


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Slide 32

Well Formed XML

The end tag matches the corresponding start tag, and there is:

No overlapping in element definitions.

No instances of multiple attributes with the same name for one element

Syntax conforms to the XML Specifications

Start-tags all have matching end-tags (or are empty-element tags).

Element tags do not overlap.Attributes have unique names.

Markup characters are properly escaped.

Elements form a hierarchical tree, with a single root node.

There are no references to external entities, except if a DTD is

provided.


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Slide 33

Well formed XML - example

Suraj

Kumar

Verma

IT Services

C2

, even these symbols don't bother it.]]>

AbhiDhar

R&D Services


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Slide 34

Four Common Errors in XML Syntax

Forget End TagsForget That XML Is Case Sensitive

Introduce Spaces in the Name of Element

John Doe

Forget the Quotes for Attribute Value

513-555-8889


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Thank you

XML Technology, Semester 4

SICSR Executive MBA(IT) @ MindTree, Bangalore, India

By Neeraj Singh (toneeraj(AT)gmail(DOT)com

)
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