XML in Brief

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XML in Brief

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Title: XML in Brief

1
XML in Brief
http//www.srdc.metu.edu.tr/ibrahim/courses/cse53
7/
2
XML Extensible Markup Language

Extensible Markup Language has become the
universal standard for representing data and
metadata
A subset of SGML Standard Generalized Markup
Language
Defined by W3C http//www.w3.org/TR/REC-xml
Started out as a standard data exchange format
for the Web (can be considered as a successor of
HTML)
It has quickly become the fundamental instrument
in the development of Web-based online
information services and electronic commerce
applications
Almost all recent electronic commerce standards
are based on XML

3
XML

Provides the ability to describe data in an open
text-based format and thus it can easily be
delivered by using standard http protocol
Content-oriented tagging provides
self-describing, both machine and human-readable
data
HTML enables a universal method of displaying
data XML provides a universal method for
describing data
Many applications on the Web use XML for hosting
large amounts of structured and semi-structured
data
Representation of information in XML documents
has been increasing at an astonishing pace
According to Meta Group, by 2005, about 65 of
corporate data will be stored in XML format

4
Maturity of Web Infrastructure
Technology
Standard
Innovation
Browse the Web
Program the Web
5
XML helps address the challenge

The data is self-describing
e.g. the meaning of the data is included
identifiers surround every bit of data,
indicating what it means
Very flexible method of representing transmitted
information
e.g. batch orders sent together can have
different fields and format without breaking apps
on each end
Open, standard technologies for moving,
processing and validating the data
e.g. the XML parser can automatically parse,
validate, and feed the information to an
application, instead of every application having
to include this functionality in Object-Oriented
environment

6
XML An Example
Data stream in a typical interface
Electronic Commerce, 100, Jones, 25,
Addison-Wesley
Same data stream in XML
ltBOOKgt ltTITLEgt Electronic Commerce
lt/TITLEgt ltQUANTITYgt 100 lt/QUANTITYgt ltAUTHORgtJone
slt/AUTHORgt ltPRICEgt25lt/PRICEgt ltPUBLISHERgtAddison-
Wesleylt/PUBLISHERgt lt/BOOKgt
7
Mark up (or Tagging)

XML uses textual markups to define data
An XML document is comprised of a collection of
tagged elements each containing
a start tag (lttagnamegt),
an end tag (lt/tagnamegt),
and the content between the two tags as follows
lttagnamegt content lt/tagnamegt
Example
ltPONumbergt 1234ABCD lt/PONumbergt

8
Tagging Data in XML
ltPONumbergt 1234ABCD lt/PONumbergt

Considering the content only, it is not possible
to understand what 1234ABCD stands for
The tag name PONumber intuitively tells that the
content is a purchase order number
Similarly, an XML element might be tagged as
name, gender, birth date, salary, price,
XML is extensible in the sense that users can
create their own tag names which are neither
predefined nor limited

9
Structure of XML Documents

XML models tree type hierarchical
semi-structured data
A valid XML document usually contains a single
root element, which constitutes the top-level of
nesting
Tagged elements may be nested to any depth to
provide structured data, or may be repeated to
represent a list of values, or a mixture of those
XML also provides attributes to describe
additional information or properties of elements

10
Processing Instructions

Provides commands or information to an
application that processes the document
lt?targetApp instructions?gt
targetApp is the name of the application that
is expected to do the processing
instructions is a string of characters that
contains the information to be passed to the
processor

11
Processing Instruction Example

ltin.stock.quantitygt
lt?EXECUTE typePL/SQL
nameretrieve.in.stock.quantity
sourceSELECT avail_Qty
FROM inventory_table
WHERE prodID123 ?gt
lt/in.stock.quantitygt

12
XML Namespaces

Namespaces are a simple and straightforward way
to distinguish names used in XML documents, no
matter where they come from
It provides a way to give elements and attributes
programmer-friendly names that will be unique
across the whole Internet
The prefixes are linked to the full names using
the attributes on the top element, whose names
begin xmlns
The prefixes are just shorthand placeholders for
the full names, which are indeed URLs (that is,
Web addresses)

13
Example

lt?xml version"1.0" encoding"UTF-8"?gt
lt!ENTITY rdf.common.schema SYSTEM
"http//www.srdc.metu.edu.tr/sc/common/common.sche
ma.rdf"gt
ltrdfRDF
xmlnsrdf"http//www.w3.org/TR/WD-rdf-syntax
"
xmlnsdc"http//purl.org/metadata/dublin_cor
e"
rdf.common.schema
ltrdfDescription about"http//www.srdc.metu.edu
.tr/sc/M1/M1.catalog.xml"gt
ltdcTitlegtM1's Electronic Cataloglt/dcTitlegt
ltdcSubjectgtManufacturerlt/dcSubjectgt
ltdcTypegtElectronic_Cataloglt/dcTypegt
ltdcFormatgtCBL 1.2 - catalog.dtdlt/dcFormatgt
ltdcIdentifiergt"www.srdc.metu.edu.tr/sc/M1/M1.
catalog.rdf"lt/dcIdentifiergt
ltdcDategt1999-02-02lt/dcDategt
ltdcDescriptiongtThis resource contains the
electronic catalog for
manufacturer M1 in XML conforming to
CBL 1.2 lt/dcDescriptiongt
lt/rdfDescriptiongt
lt/rdfRDFgt

14
Document Type Definition
15
Example XML document

lt?xml version1.0 ?gt
ltPurchaseOrderRequestgt
ltPONumbergt1234ABCD lt/PONumbergt
ltPurchaseOrderDategt20030601lt/PurchaseOrderDategt
ltLineItemgt
ltItem_Identification No9344 /gt
ltQuantityOrderedgt 16 lt/QuantityOrderedgt
ltUnitPricegt 95 ltUnitPricegt
lt!-- this is the discount price we
get --gt
lt/LineItemgt
ltLineItemgt lt/LineItemgt
lt/PurchaseOrderRequestgt

16
Giving Structure to Data
PurchaseOrderRequest
PurchaseOrderDate
LineItem
PONumber
Item_Identification
QuantityOrdered
UnitPrice
17
DTD Document Type Definition

The principle purpose is to declare the
hierarchy of document elements
A document type definition defines
The name of the elements,
The content model of each element,
How often and in which order elements may appear,
If the end-tags can be shortcut,
The possible presence of attributes and their
default values,
The names of the entities

18
An Example DTD

lt?xml version1.0 encodingUTF-8?gt
lt!DOCTYPE simple
lt!ELEMENT PurchaseOrderRequest (PONumber,
PurchaseOrderDate, LineItem)gt
lt!ELEMENT LineItem (Item_Identification,
QuantityOrdered,
UnitPrice)gt
lt!ELEMENT Item_Identification(PCDATA)gt
lt!ELEMENT QuantityOrdered (PCDATA)gt
lt!ELEMENT UnitPrice (PCDATA)gt
lt!--This is a comment line to state that the
other elements are skipped --gt ...gt

19
DTD Syntax Rules

A DTD specifies the structure of an XML element
by declaring the names of its sub-elements and
attributes
Sub-element structure is specified using the
operators
, (comma) Sequence indicator
(asteriks) Set with zero or more elements
(plus sign) Set with one or more elements
? (question mark) Optional
(verticle bar) Or
() (paranthesis) Grouping
Main constructs of DTDs
Elements
Attributes
Entities

20
Main Constructs of DTD

Elements
lt!ELEMENT element-name content-typegt
where
content-type EMPTY PCDATA
(sub.element.list) ANY
EMPTY Element may not have a content.
PCDATA Element may have character data content,
but may not
contain any tagged data (sub
elements).
ANY The element may contain character
data and/or any
tagged data, these may be mixed in
any order.

21
Element Definition Examples

lt!ELEMENT male EMPTYgt
Use in XML document ltmalegt lt/malegt
or its shortcut ltmale/gt
lt!ELEMENT bold (PCDATA)gt
Use in XML document ltboldgt you can write a
note herelt/boldgt
(The data inbetween may not contain special
chars. such as lt gt )
lt!ELEMENT parag (PCDATA bold) gt
(mixed content)
Use in XML document ltparaggt This is a
paragraph with ltboldgt bold
lt/boldgt and regular ltboldgt
textlt/boldgt lt/paraggt

22
Element Definition Examples

Sequence lt!ELEMENT elem (A, B) gt
Use in XML document ltelemgt ltAgt...lt/Agt
ltBgt...lt/Bgt lt/elemgt
Choice lt!ELEMENT elem (A B) gt
Use in XML document ltelemgt ltAgt...lt/Agt lt/elemgt
Combination lt!ELEMENT elem (A, (B C), D) gt
Use in XML document ltelemgt ltAgt...lt/Agt
ltBgt...lt/Bgt ltDgt...lt/Dgt lt/elemgt
Grouping lt!ELEMENT elem (A,(((BC),D),(EF))?
) gt
Use in XML document ltelemgt ltAgt...lt/Agt lt/elemgt
lt!ELEMENT freedata ANYgt
Use in XML document ltfreedatagt This
ltverbgtislt/verbgt a ltboldgt bold lt/boldgt ltbluegt
ltobjgt text lt/objgt lt/bluegt lt/freedatagt

23
Main Constructs of DTD

Attributes
lt!ATTLIST element-name
attribute-name attribute-type
presence-spec default-value
gt
element-name Name of the element that
attributes are defined for.
attribute-name Name of the attribute
being defined.
attribute-type Indicates the list of values
that an attribute may have.
presence-spec Defines the presence
requirements of the attribute
FIXED The attribute always has the same
fixed value, thus
it does not need to be presented with
the element.
IMPLIED The attribute takes the given value
if it is presented.
REQUIRED The attribute must always be
presented with the element.

24
Attribute Definition Examples

lt!ELEMENT price (PCDATA)gt
lt!ATTLIST price
currency CDATA
REQUIRED gt
Use in XML document ltprice currencyUSDgt123.
50 lt/pricegt
(Conforms to DTD even if currency code is
mistakenly written as UST !)
lt!ATTLIST price
currency (USD CAD
GBP TRL) REQUIRED gt
lt!ATTLIST price
currency (USD CAD
GBP TRL) TRL gt
lt!ATTLIST price
currency CDATA IMPLIED
gt

25
Main Constructs of DTD

General Entities
lt!ENTITY entity-name entity-valuegt
Entities are used to define shortcuts to common
text or common definitions.
Entities can be either internal or external.
Internal entity
lt!ENTITY cValue this is an example of
commonly used text gt
External entity
lt!ENTITY cValue SYSTEM http//www.abc.com/com
montxt.xmlgt
Use in XML document lttextgt cValue lt/textgt

26
Main Constructs of DTD

Parameter Entities
lt!ENTITY entity-name entity-valuegt
Parameter entities can only be used in DTDs.
Using an example parameter entity
lt!ENTITY myURL http//www.abc.com gt
lt!ENTITY cValue SYSTEM myURL/commontxt.xml
gt
Or
lt!ENTITY dataType INTEGER FLOAT
STRING gt
lt!ATTLIST varName
varType (dataType) REQUIRED gt

27
Limitations of DTD

Extremely limited Data Typing (no Integer, Float,
Enumaration or formatted data descriptions, etc.)
Very limited power to describe number of
occurences of an element (remember , , ?)
No support for inheritance in schema definitions,
which results in very large DTDs
Not enough support for self-documentation
DTD is not XML DTDs are written in their own
language, not in XML

28
XML Parsers
29
XML Parsers

A parser takes an XML document and makes its
structure and content available to an application
through an API
There are two main Application Programming
Interfaces (APIs) for writing parsers
Document Object Model (DOM) and
Simple API for XML (SAX)
Today, many parsers are both DOM and SAX compliant

30
The SAX API

The Simple API for XML is an event-based parser.
It reads XML document from beginning to end, each
time it recognizes a construct, it raises a
relevant event.
For example
When lt comes, startElement is raised
When lt/ comes, endElement is raised
When data comes, characters event is raised
SAX parser can not modify XML document
Events are actually methods of ContentHandler
object.

31
An example SAX API

ltPurchaseOrderRequestgt parser calls
startElement
ltPONumbergt 1234ABCD lt/PONumbergt parser calls
startElement, characters, and endElement
ltPODategt20030601lt/PODategt parser calls
startElement, characters, and endElement
ltQuantitygtltboxgt3lt/boxgtlt/Quantitygt parser
calls startElement, startElement, characters,
endElement and endElement
lt/PurchaseOrderRequestgt parser calls endElement

32
XML DOM Parser
A parser validates and makes the data contained
in an XML document available to the application
33
XML StyleSheet Language (XSL)
34
Extensible Stylesheet Language

XSL describes the presentation of data
Three parts of XSL
XSLT (language for transforming XML documents)
XPath (language for extracting parts of an XML
document)
XSL Formatting Objects (vocabulary for formatting
XML documents)

35
XSL Functions

Transforms XML into any other language or format
Filters and sorts XML data
Extracts parts of an XML document
Formats XML data based on the data value (like
displaying negative numbers in red)
Outputs XML data to different devices, like
screen, paper or voice (SpeechML)

36
XML Style Sheet Processing
SOURCE SOFTWARE AG
37
(No Transcript)
38
XSLT Processor

Converts an XML document to another form
An XSL style sheet is a set of transformation
instructions for converting a source XML document
to a target document

39
Multiple uses of data with XML XSL

Data is created once and can be delivered in many
different formats

SOURCE OASIS
40
Impact of XML

Interchange mechanism between applications
Rapidly becoming the database language of the Web
XML client/server/server transactions over HTTP
XML properties
Scalable
Maintainable
Easy to use (spreadsheet style skills)
Interoperable (exchange business components)

41
Why use XML?
42
Why use XML?

It is a W3C recommendation and has become a
universally accepted standard way of structuring
data and meta-data (syntax)
It models tree/forest type hierarchical
semi-structured data,
It facilitates implementation-level
interoperability by providing hardware-representa
tion-free data exchange
Anyone can invent new tags for any purpose and
define their meaning in DTDs or schemas,
Content-oriented tagging provides self-describing
and human-readable data
Strong industrial and academic support,
A lot of free or inexpensive tools
Expected to be dominant data representation
format on the Internet in the near future.

43
XML versus EDI
44
XML vs EDI
45
XML vs EDI
46
Interoperability and XML
47
Extensibility in XML

Anyone can invent new tags and attach a meaning
to those tags
For example
ltHandHeldDevicegt This devicelt/HandHeldDevicegt
ltMobileDevicegt This devicelt/MobileDevicegt
But if every user creates its own XML definition
for describing his data, it is not possible to
achieve interoperability

48
Agreement on tags is necessary