4D Summit Europe 2014 - Conférence d'A&C Consulting "XML Demystified"

XML demystiﬁed
4D Summit Europe 2014

4D Summit 2014 • Paris • Celebrating 30 years
Bruno LEGAY
Responsable Bureau d’Etudes
A&C Consulting
www.ac-consulting.fr

What is xml ?

What is xml ?
• Markup langage

What is xml ?
• Markup langage
• Serialization

What is xml ?
• Markup langage
• Serialization
• Data structure

What is xml ?
• Markup langage
• Serialization
• Data structure
• Data exchange

What is xml ?
• Markup langage
• Serialization
• Data structure
• Data exchange
• Data storage

Where is xml ?

Where is xml ?
• Web (xml-rpc, web-services/SOAP,Ajax, Rss, Atom,
Rest, xhtml)

Where is xml ?
Rest, xhtml)
• Ofﬁce documents

Where is xml ?
Rest, xhtml)
• User interface (XUL/XAML)

Where is xml ?
Rest, xhtml)
• Preference ﬁles (4D, OS X, etc...)

Where is xml ?
Rest, xhtml)
• Svg

Where is xml ?
Rest, xhtml)
• Svg
• etc...

History of XML
Where does it come from ?

GML
1969 : Generalized Markup Language (IBM)!
Documentation

GML
SGML
1986 : Standard Generalized Markup Language (ISO)!
Documentation
Documentation

GML
SGML
1991 : Hypertext Markup Language (CERN/W3C)!
Hypertext documents
Documentation
Documentation
HTML

GML
SGML
XML
Hypertext documents
1998 : eXtensible Markup Language (W3C)!
Anything
Documentation
Documentation
HTML

GML
SGML
XML
XHTML
2000 : XHTML (W3C)!
Hypertext documents
Anything
Documentation
Documentation
HTML

GML
SGML
XML
XHTML
HTML5
2008 : HTML5 (WHATWG / W3C)
2000 : XHTML (W3C)!
Hypertext documents
Anything
Documentation
Documentation
HTML

GML
SGML
XML
XHTML
HTML5
2008 : HTML5 (WHATWG / W3C)
2000 : XHTML (W3C)!
Hypertext documents
Anything
Documentation
Documentation
SVG
MathML
HTML

XML / HTML
XML HTML
strict loose

XML / HTML
XML HTML
strict loose
case-sensitive case-insensitive

XML / HTML
XML HTML
strict loose
<emptyTag/> <emptyTag>

XML / HTML
XML HTML
strict loose
<emptyTag/> <emptyTag>
unlimited tags predeﬁned tags

Why XML ?

Before xml

Before xml
• Flat text ﬁles

Before xml
• csv

Before xml
• csv
• Binary ﬁles

Before xml
• csv
• Binary ﬁles
• Propriatery ﬁle formats

Advantages of xml

Advantages of xml
• Meta markup language

Advantages of xml
• Flexible data structure

Advantages of xml
• Text based

Advantages of xml
• Text based
• Self documented

Advantages of xml
• Text based
• Self documented
• Easy to read

Advantages of xml
• Text based
• Self documented
• Easy to read
• Strict

Advantages of xml (cont.)

• Validity checking

• Multiple encoding support (us-ascii, macroman,
windows1252, iso-8859-1, utf-8, etc...)

• Introspection

• Introspection
• Namespaces

• Introspection
• Namespaces
• Rich toolset

• Introspection
• Namespaces
• Rich toolset
• Compression friendly

• Introspection
• Namespaces
• Rich toolset
• Compression friendly
• Comments

Examples
start tag end tag
attribute

Empty elements

Element vs Attribute
Element Attribute
Unique no yes

Element Attribute
Unique no yes
Ordered yes no

Element Attribute
Unique no yes
Ordered yes no
Can have children yes no

Element Attribute
Unique no yes
Ordered yes no
Can have attributes yes no

Element Attribute
Unique no yes
Ordered yes no
Can have attributes yes no
Normalized no yes

Hierarchy

Common mistake
redundant information

XML document

XML document
prolog

XML document
prolog
xml declaration

XML document
prolog
xml declaration
Document type declaration

XML document
prolog
xml declaration
root element
Document type declaration

XML prolog
<?xml version="1.0" encoding="UTF-8" standalone="no"?> 
<!DOCTYPE html> 
…

XML prolog
• Prolog is optional
<!DOCTYPE html> 
…

XML prolog
• XML declaration is optional
<!DOCTYPE html> 
…

XML prolog
• version is mandatory (usually “1.0”)
<!DOCTYPE html> 
…

XML prolog
• encoding is optional (default “UTF-8”)
<!DOCTYPE html> 
…

XML prolog
• standalone is optional (default “no”)
<!DOCTYPE html> 
…

XML prolog
• DTD (Document Type Deﬁnition) is optional
<!DOCTYPE html> 
…

XML prolog
• DTD (Document Type Deﬁnition) is optional
• Unicode BOM (Byte Order Mark) is allowed
<!DOCTYPE html> 
…

Comments
comments

Predeﬁned entities
Name Character Unicode xml html
quot " U+0022 (34) xml 1.0 html 2.0
amp & U+0026 (38) xml 1.0 html 2.0
apos ' U+0027 (39) xml 1.0 xhtml 1.0
lt < U+003C (60) xml 1.0 html 2.0
gt > U+003E (62) xml 1.0 html 2.0

Character entity decimal :
Character entities

Character entity decimal :
Character entity hexadecimal :
Character entities

Custom entities
Declaration :

Custom entities
Declaration :
Usage :

Namespace
Default namespace

Namespace
Default namespace
Custom namespace

Mixed content

PCDATA (parsed) vs CDATA (unparsed)

Validation

Validation
• “Well formed” : xml syntax is ok

Validation
• Well formed is mandatory

Validation
• “Valid” : schema follows DTD or Schema (.xsd)

Validation
• DTD or Schema describe the structure of an xml
document

Validation
• DTD or Schema describe the structure of an xml
document
• Validation is optional (but it will make your code
simpler and more resilient)

DTD vs Schema
DTD Schema
Extension .dtd .xsd

DTD vs Schema
DTD Schema
Extension .dtd .xsd
Syntax specific xml

DTD vs Schema
DTD Schema
Extension .dtd .xsd
Syntax specific xml
Embedded possible no

DTD vs Schema
DTD Schema
Extension .dtd .xsd
Syntax specific xml
Flexibility good best

DTD vs Schema
DTD Schema
Extension .dtd .xsd
Syntax specific xml
Type checking limited powerful

DTD vs Schema
DTD Schema
Extension .dtd .xsd
Syntax specific xml
Custom entity yes no

DTD vs Schema
DTD Schema
Extension .dtd .xsd
Syntax specific xml
Custom entity yes no
Part of XML specs yes no

DTD example

External DTD example

Schema example

XPath

XPath
• XPath allows selection of nodes of an xml document with
expressions

XPath
expressions
• Indexed selection
/children/child[2]

XPath
expressions
• Indexed selection
/children/child[2]
• More powerful selection (functions, boolean operators, etc...)
/children/child[@name="Orville"]

XSLT

XSLT
• Extensible Stylesheet Language Transformations

XSLT
• XSLT purpose is to process an xml document and generate an
output (xml, html, text, etc...)

XSLT
• XSLT purpose is to process an xml document and generate an
output (xml, html, text, etc...)
• Relies on XPath

Storage

Storage
• Text or blob ?

Storage
• Text or blob ?
• Text encoding can be ambiguous if non Unicode is
used

Storage
• Text or blob ?
used
• Blob can be compressed

Storage
• Text or blob ?
used
• Blob can be compressed
• Check that your xml is well formed

Tools

Tools
• Basic text editor (TextEdit, Notepad, vi, etc...)

Tools
• Advanced text editor (TextWrangler, Notepad++, etc...)

Tools
• XML Editor (oXygen, XMLSpy, etc...)

Tools
• XML Editor (oXygen, XMLSpy, etc...)
• xmllint (part of libxml2)

Dealing with XML in 4D

• Don’t treat xml as a text ﬁle, use xml commands

• 4D (SAX, DOM, Schemas, XSLT)

• SAX, DOM and Schemas : Xerces

• XSLT : Xalan

• XSLT : Xalan
• “XSLT plugin” (Miyako) : libxml

• XSLT : Xalan
• XML Plugin (Pluggers) : Libxml & Libxslt

• XSLT : Xalan
• XML Plugin (Pluggers) : Libxml & Libxslt
• Expat 4D (Mark Mitchenall) : based on Expat

SAX / DOM

SAX / DOM
• 4D has two parser APIs

SAX / DOM
• SAX : Simple API for XML

SAX / DOM
• SAX parser reads a ﬁle sequentially

SAX / DOM
• DOM : Document Object Model

SAX / DOM
• W3C standard for xml and html

SAX / DOM
• W3C standard for xml and html
• DOM parser loads the xml “in memory”

SAX vs DOM
SAX DOM
Memory footprint small proportional

SAX vs DOM
SAX DOM
Document Size big small

SAX vs DOM
SAX DOM
Scalablity good limited

SAX vs DOM
SAX DOM
Validation no yes

SAX vs DOM
SAX DOM
Validation no yes
Xpath no yes

SAX vs DOM
SAX DOM
Validation no yes
Xpath no yes
Type Read|Write Read+Write

SAX vs DOM
SAX DOM
Validation no yes
Xpath no yes
Modification no yes

SAX vs DOM
SAX DOM
Validation no yes
Xpath no yes
Modification no yes
Target File
File, text,
blob, http

SAX vs DOM
SAX DOM
Validation no yes
Xpath no yes
Modification no yes
Target File
File, text,
blob, http
* SAX is a read only API. 4D has a “SAX” parser/reader. 4D has also a sequential xml writer named “SAX”.

DOM with large XML...

SAX Examples

Sax parsing

Sax writing

DOM Examples

Parse

HTTP get + parse

Sample xml

New xml document

Count all child elements

List all child elements

List all attributes

Pitfall

Process 4D Tags

Office ﬁle formats

Office file formats
OpenDocument Office Open XML
OASIS Microsoft
Open Office MS Office : Word, Excel
odf
WordML
SpreadsheetML
ooxml
2005 2003 2007
.odt, .ods,
etc...
.xml
.docx, .xlsx,
etc...
zip + xml xml zip + xml

SVG

SVG
• SVG :“ScalableVector Graphics” image format

SVG
• xml based

SVG
• xml based
• Light, scales smoothly

SVG
• xml based
• Supported in most modern browser

SVG
• xml based
• Supported in 4D (natively)

SVG
• xml based
• Supported in 4D (natively)
• 4D provides “SVG Component” and “SVG Area”

SVG example

SVG in plain 4D

SVG with “4D SVG”
component

C_OBJET and
JSON

JSON format

JSON example
<children><child dob="1867-04-16" name="Wilbur"/><child dob="1871-08-19" name="Orville"/></children>
{"child":[{"name":"Orville","dob":"1871-08-19"},{"name":"Orville","dob":"1871-08-19"}]}
JSON :
XML :
JSON compact :
XML compact :

C_OBJECT to JSON
code

JSON to C_OBJECT
code

Can C_OBJECT work
with XML ?

C_OBJECT to XML
code

C_OBJECT to XML
code (cont.)

XML vs JSON
XML JSON
Approach tree list

XML vs JSON
XML JSON
Approach tree list
Arrays no yes

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8
Comments yes no

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8
Comments yes no
Mixed mode yes no

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8
Comments yes no
Mixed mode yes no
Namespace yes no

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8
Comments yes no
Mixed mode yes no
Namespace yes no
Conformity dtd, schema no

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8
Comments yes no
Mixed mode yes no
Namespace yes no
Direct Access yes (xpath) no

XML vs JSON
XML JSON
Approach tree list
Arrays no yes
Encoding many utf-8
Comments yes no
Mixed mode yes no
Namespace yes no
Direct Access yes (xpath) no
Transformation yes (xslt) no

XML vs JSON (in 4D)
XML JSON
Debugger friendly no yes

XML vs JSON (in 4D)
XML JSON
Native type no yes

XML vs JSON (in 4D)
XML JSON
Native type no yes
Memory leak possible no

XML vs JSON (in 4D)
XML JSON
Native type no yes
Large documents yes (sax) no

XML vs JSON (in 4D)
XML JSON
Native type no yes
Large documents yes (sax) no
Available since 4D v2003 4D v14

Does JSON make XML
obsolete ?

Why XML is still
relevant

Why XML is still
relevant
• XML is an industry standard

Why XML is still
relevant
• XML has rich tool set

Why XML is still
relevant
• JSON features are a subset of XML features

Why XML is still
relevant
• JSON is relevant in a “small” subset of XML
“market” (web 2.0, web-services)

Why XML is still
relevant
• Performance gain should be measured not guessed

Why XML is still
relevant
• Web-Services APIs can provide both XML and JSON

Why XML is still
relevant
• Web-Services APIs can provide both XML and JSON
• Choice is good

Demonstration

Thank you!
http://www.w3.org/TR/xml/
http://www.w3.org/TR/xml11/
http://www.w3schools.com
http://www.oxygenxml.com/
http://www.saxproject.org
https://github.com/miyako/4d-plugin-xslt

Thank you!
Bruno LEGAY
Responsable Bureau d’Etudes
A&C Consulting
www.ac-consulting.fr

4D Summit Europe 2014 - Conférence d'A&C Consulting "XML Demystified"

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