xml – 1h. xml: contents what is xml? what is “well formed” xml? what is “valid” xml?...
TRANSCRIPT
XML – 1h
XML: Contents
• What is XML?
• What is “Well Formed” XML?
• What is “Valid” XML?– Document Type Definitions– Scalable Vector Graphics (SVG)
• XML in 10 Points
• Some Questions for You
What is XML?
XML is a method of putting structured data in a file format. It is not a programming language; it doesn’t DO anything
• An XML document includes text and mark-up; just like HTML.
• XML permits new markup tags to be defined
• XML is rather more strict than HTML
<?xml version="1.0" standalone="no"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "../../svg11-flat.dtd">
<svg width="12cm" height="4cm" viewBox="0 0 1200 400" xmlns="http://www.w3.org/2000/svg" version="1.1">
<circle cx="600" cy="200" r="100" fill="red" stroke="blue" stroke-width="10" />
<rect width="20" height="10"/>
<text>Kilroy was here.</text></svg>
An Easy Example (SVG)
What is “Well Formed” XML?
• 1. Taken as a whole, it matches the production labelled document.
• 2. It meets all the well-formedness constraints given in the W3 specification.
• 3. Each of the parsed entities which is referenced directly or indirectly within the document is well-formed.
…I find this a bit vague…
What is “Well Formed” XML?
• There are Elements, Tags and Character Data, eg:
<person> Alan Turing</person>
• The whole example was a person Element. • Alan Turing was Character Data• <person> was a tag
What is “Well Formed” XML?
• Elements MUST be closed
• Tags may be opening or closing tags of elements
• Alternatively, single tags may be closed by a slash, eg
<img src=“picture.gif” />
• Elements may also be empty
What is “Well Formed” XML?
• Tags have Names and Attributes <p font=“ariel”>
(p was a name; font was an attribute)
• XML is case sensitive, so the name “BR” is regarded as different to “br”
• XML must be well nested: <b><i> Horrors!!! </b></i>
What is “Well Formed” XML?
Names and attributes may contain:
• A…Z, a…z or the characters of ANY alphabet (eg: ي...א )
• Numbers 0…9• Underscore_ • Hyphen- • Period.• That’s it.
What is “Well Formed” XML?
• Tags must be closed.
• Elements may contain elements - nesting must "proper".
• Tags may contain attributes.
• Characters such as < and & must be "escaped" as < and & - they have a special significance in XML and may not appear in data unescaped
What is “Well Formed” XML?
• Must begin with the XML declaration• Must have one unique root element• All start tags must match end-tags• XML tags are case sensitive• All elements must be closed• All elements must be properly nested• All attribute values must be quoted• XML entities must be used for special characters
What is “Well Formed” XML?
• Well-formedness is not the same as Validity (see later)
Amazingly strict rule:
• If a parser encounters a well-formedness violation while parsing a document, it MUST STOP (usually with a useful error message)
Pop Quiz
5 Minutes Maximum!
WHICH OF THESE IS WELL-FORMED?
?<p><b>but soft!</b> what <i>light</i> through…</p>
<stuff><stuff>bits</stuff>&<pieces></stuff>
<tree>I think <tree>that I will never see <tree>a poem</tree> lovely as <tree>a tree</tree> </tree></tree>
<a href="http://www.w3.org">link</a>
<p>a picture<img src="pic.gif"><br>Next line</p>
<p>a picture<img src="pic.gif"/><br></br></p>
<p>We may be sure that within the realm of real numbers x*x<0 is never true.</p>
<a href='http://www.o'reilly.com'>Nutshell Series</a>
And of course and ampersand may be escape-escaped &amp;
Pop Quiz
Truth is relative.
Let’s vote on the answers.
What is “Valid” XML?
If an XML document is well-formed we may ask if it is valid. A valid XML document is one that agrees with the additional rules set out in a DTD (document type definition). The DTD includes:
• ELEMENT: These dictate what kind of child
nodes each element is permitted.• ATTLIST: This indicates what kind of attributes
are permitted.
Scalable Vector Graphics (SVG)
• (In bit-map graphics we specify the colour of each pixel in a grid). This isn’t it.
• Instead, we describe objects to be rendered. • Allows us to produce graphics (boxes, lines,
curves, text) in a scalable format. • Arbitrarily high resolution with constant file size. • Similar to Flash (but Flash has binary format)• Designed and controlled by W3C
<?xml version="1.0" standalone="no"?><!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "../../svg11-flat.dtd">
<svg width="12cm" height="4cm" viewBox="0 0 1200 400" xmlns="http://www.w3.org/2000/svg" version="1.1">
<circle cx="600" cy="200" r="100" fill="red" stroke="blue" stroke-width="10" />
<rect width="20" height="10"/>
<text>Kilroy was here.</text></svg>
An Easy Example (SVG)
Scalable Vector Graphics (SVG)
• Good example of an XML application.
• Standard defined by www.w3.org
• W3C supply a DTD and a description of how each element should be interpreted
• Anyone can produce a processor for the language
• Anyone can produce content.
Narrative and Record Documents
• XML documents normally fall into two categories:
• An XHTML description of a web page starts at the beginning of the document and works its way down to the end
• An XML description of a spreadsheet simply describes the data (there isn’t a beginning or an end)
Narrative and Record Documents
• An XHTML web page is an example of a Narrative document
• A spreadsheet in Microsoft Office Open XML (OOXML) is an example of a record document.
XML in 10 Points
1. XML lets you put structured data in a text file
2. XML looks like HTML but isn't HTML
3. XML is text, but isn't meant to be read
4. XML is a family of technologies
5. XML is verbose, but that is not a problem
XML in 10 Points
6. XML is new, but not that new
7. XML is license-free
8. XML is platform-independent
9. XML is well-supported
10. XML is a W3 standard
11. For what it does, there are no competitors
Recap of Unit
• What is XML?
• What is “Well Formed” XML?
• What is “Valid” XML?– Document Type Definitions– Scalable Vector Graphics (SVG)
• XML in 10 Points
• Some Questions for You