Overview of XML-related standards

Steven J. DeRose, Ph.D.

Brown University
Scholarly Technology Group

Steven_DeRose@brown.edu
http://www.stg.brown.edu/~sjd

XML and related specs

XML: The basic syntax

Plus Namespaces, Schemas, InfoSet

DOM: API to the Information Set

XML Linking

XPath: Expressions to find XML nodes

XPointer: XPath++ for addressing

XLink: hypermedia connections

Stylesheet Attachment

XSL: stylesheets and transforms

XML specification

A “Recommendation” since 2/1998

The highest level for a W3C specification

Defines the syntax/grammar

Not any particular processing/semantics

Schemas or DTDs define applications (poem, manual, eCommerce,...)

All these can be parsed by generic XML, just as new words can be readily fitted into existing sentence structures

Schemas are political as well as technical

XML Namespaces

Disambiguate element type names

<head><html:title>Oncataloging</html:title>…
<biblio><entry id='DeRo98'>
<loc:title>Navigation, Access, Control…

Declaring prefixes

<sec xmlns:loc="http://foo.com/mynamesp”
xmlns:html='http://www.w3.org/1999/xhtml'
xmlns="http://…"> <loc:title>…

Declaration without prefix sets default

Attributes can have namespaces

No renaming (x:foo to y:bar)

XML Schemas

Let you define a document type

What elements/attributes are defined?

Where can they occur?

What content is allowed?

What datatypes are represented?

Required for validation

Similar to DTDs, but

More powerful (esp. for datatyping)

Use XML syntax

XML Information Set

What data in XML document “counts”?

Elements, attributes, content

Order and hierarchy of nodes

Required for interoperability

Applications must count nodes consistently

Not whitespace inside tags

Not which kind of quotes around attributes

Candidate recommendation 2001-05-14

http://www.w3.org/TR/xml-infoset

7 types of Infoset Nodes

Root: Above the document

<?foo ?> <doc>…</doc> 

Element: Main structure

<div n='1'>…</div>

Text: Spans of unbroken text

Attribute: Properties of elements

Namespace: Prefixes/URIs

Processing Instr: <?…?>

Comment:

Example

More Infoset details

DOM

"Document Object Model"

An API for accessing the Infoset

Many tools use this

Level 1 complete

http://www.w3.org/TR/REC-DOM-Level-1

Level 2 core complete

http://www.w3.org/TR/DOM-Level-2-Core

XML Base

Similar to the HTML <base> element

Useful for keeping URIs simpler and uniform.

Applies to relative URLs

<html>
<head>
<base href="http://www.example.com/">
…</head>

<body>… <a href="fig/mosquito.png">

The hrefs combine to make whole URI:

http://www.example.com/fig/mosquito.png

XML Base

XML Base provides similar feature

By a reserved attribute

<?xml version="1.0"?>

<doc xml:base="http://eg.org/today/">

See <link xlink:type="simple" xlink:href="new.xml">the news</link>

Applies to attributes & descendants

Can be overridden on descendants

Final REC as of 2001-06-27

http://www.w3.org/TR/xmlbase/

Stylesheet attachment

Lets documents point to stylesheets

Based on HTML <link type='stylesheet'>

Multiple, anywhere in XML prolog

May point to CSS, XSL, etc.

Example:

<?xml-stylesheet alternate="yes" href= "mystyle.css" title="Medium" type="text/css"?>

Equivalent of HTML:
<LINK href="mystyle.css" title="Medium" rel="alternate stylesheet" type="text/css">

REC: http://www.w3.org/TR/xml-stylesheet

XSL specification

Stylesheet language

Based on ISO DSSSL and W3C CSS

2 major pieces:

XSLT: document transformation

Builds on XPath (more later)

Match elements, then construct output

XSL-FO: Formatting objects

To actually render blocks, fonts, tables, etc.

Hypermedia support unfinished (=CSS)

http://www.w3.org/TR/xsl/

Current XML organization

XML Plenary coordinates
several WGs

XML-Linking specifications

XPath: expressions on infoset nodes

REC: http://www.w3.org/TR/xpath

XPointer: XPath + ranges, in URIs

CR: http://www.w3.org/TR/WD-xptr

XLink: gather locations to make links

REC: http://www.w3.org/TR/xlink/

(XML Base)

XML-Linking goals: end user

Links from un-writable documents

Which is most of the Web, for any person

Perhaps the most important single feature

->Bidirectional and multi-ended links

->Annotations and annotation sharing

Dynamic updates, patches, highlighting

Precise link attachment in any media

Large sets/databases of managed links

An entirely new market for links per se

Anyone can publish/sell their commentary

Pointing vs. linking

In HTML, many things are combined:

<a href="eg.org/foo">wow</a>

Technically:

"eg.org/foo" is a pointer (namely a URI)

The abstract connection itself is the link

The <a> element is a link representation

"wow" is the local anchor

Anchors are also called link-ends

Data at eg.org is the remote anchor

HTML specifies the link behavior

XPointer: locators

XLink: connections

Describes a relationship
of referenced location(s),

To each other

To descriptions

XLink provides
some key ones

XPointer…

Locates parts of XML resources

Even things without IDs

Even things that aren't whole nodes

XPointer adds (beyond XPath):

Way to refer to point and range selections

Way to use inside URI fragment identifiers

TEI “extended pointer” notation plus XPath logical expressions

Typically, a browser might load a document and scroll to/highlight the part

Anatomy of a URI reference

Fragment identifiers

Part of URIs after "#"

Says where in document is actual target

Separate form for each media type

Identifiers for graphics ¹ for text

IETF MIME definition specifies form

HTML

To scroll to <a name="coyote">

http://example.com/hello.html#coyote

The 3 XPointer/XPath forms

Bare names

An XML "name"* finds element with that ID

For (X)HTML compatibility

HTML uses "NAME", not ID

Child sequences

Stepwise down through elements: /1/4/27/2

May start with an ID: intro/4/3/2

Full XPointers

scheme1(args) scheme2(args)…

For now, the only "scheme" is "xpointer"

XPointer's 2 parts

Provide 'scheme' mechanism

Identify media-specific pointer types

Allow multiple ones to co-exist

Pointing methods for XML

Point to ranges, sets, id's, coords…

Point descriptively

XPointer schemes

Each media type needs pointer type

pngRect(0,10 100,200)

vrml(camera=1,2,3 light=4,50,500)

map(W0°10’/ N51°30’)

Xml(…)

Schemes label fragment identifier types

#scheme1(args) scheme2(args)…

Escape any extra ( ) -- tlg('^(apax')

XPointer() is the first scheme

Multiple schemes in a URL?

When a server responds to a URI, it

Checks what media the client can handle

Picks one of those to send

“content negotiation”

If a visually-impaired user clicks

<a href="http://www.example.com/foo.gif# gif(0,0 1,1) xpointer(id(chap1))">

The server may fall back to an XML file

The client tries fragment identifiers left-to-right, and uses the first one that works

Anatomy of a location step

Summary: axes and functions

root( ), id( )

parent, self, child

ancestor, ancestor-or-self

descendant, descendant-or-self

preceding-, following-sibling

preceding, following

attribute, namespace

here( ), origin( )

String-range(), range-to()

Counting locations

Points and Ranges

Point

What you get by click-selection

Gap before/after node or char

Range

What you get by drag-selection

From a start point to an end point

Not generally a WF XML subtree

May partially contain some elements:

<p>Hello, world.</p><p>Hi, back</p>

Crucial for creating hypertext links

How often do you click/drag exactly one entire element?

XLink is a language that...

Lets you invent your own linking elements and their meanings

In keeping with XML approach overall

Lets you create link databases

Links become first-class objects in the model

Provides some basic traversal behavior

E.g., “Open the target in a new window”

The rest is left to a style mechanism such as XSL

XLink terminology

Linking element

Identifies, connects, and describes anchors

Locator

Locateses some link end (anchor)’s data

Link end or anchor

A data portion reachable as part of a link

Arc

Explicit connection between two link ends

Resource

Anything you can point at on the Web

Using an arc is called Traversal

What links do with link-ends

A link identifies where its ends are

Using some kind of locators

URI#XPointer will be the locator for XML

URI#scheme()scheme() in general

A link attaches metadata to each end

Its formal role in relation to the other ends

A title by which to refer to it (say, in menus)

Some traversal behaviors

Arcs to say which traversals happen

Link itself can also have type, other info

Inline links

Linking element itself (better, the origin() end) is one of the link’s ends

Out-of-line links

Linking element itself isn't automatically made into one of its own resources

Anatomy of an XML link

Arcs

Arcs specify traversal rules

Multi-ended links may restrict travel among their endpoints

Restrictions generic or app-specific

Arcs enable the description of both

An arc is a pair of roles, plus metadata

Enables traversal between ends with the given roles

May be multiple locators per role (useful for document assembly, multiple-choice travel)

Arc example: fuel-type annotations

How to detect links

Could have any name and content at all

<footnote>, <criticism>, …

xlink:type attribute marks linking elements for applications to find:

<!ELEMENT footnote EMPTY>
<!ATTLIST footnote
xlink:type CDATA #FIXED "simple"
xlink:href CDATA #REQUIRED>

For example: ...has studied the issue.<footnote href="http://www.doctools.com" />

Arcs and Traversals

Traversal is split into:

Behavior

Author's intention for behavior of a link.

Input to style mechanism

Not a presentation command

Actuation

Defines the event that triggers a link

Events are very generic, intentionally

Two kinds of behavior policies

show attribute

new to traverse and provide new “context”

replace to display in existing “context”

embed to display in the body of the initiating resource

Some semantic details are left unspecified: combining multiple ends, style inheritance, etc.

actuate attribute

onRequest to require external request

onLoad to traverse when link processed

Link databases let you…

Attach descriptive information from afar

Annotate other people's stuff

Maintain links more easily

When a destination changes, you don’t have to touch documents with links to it

Engage in online commerce in links

Express, package, and sell point-of-view

Collect out of line links as databases

External Linksets

Users will have persistent linkdbs

Subscriptions, interest groups, private,...

Document can specify relevant link dbs

Linked by special type of extended link

Included within regular documents too

LinkDBs enable link management

Needed to author using external links

Example: Public annotations on….

An external Linkset Instance

<xls>
<linkbase xlink:href="linkset1.xml" />
<linkbase xlink:href="linkset2.xml" />
<linkbase xlink:href="linkset3.xml" />

</xls>



	Steven J. DeRose, Ph.D.
	Brown University Scholarly Technology Group Steven_DeRose@brown.edu http://www.stg.brown.edu/~sjd


	XML: The basic syntax
		Plus Namespaces, Schemas, InfoSet
		DOM: API to the Information Set
	XML Linking
		XPath: Expressions to find XML nodes
		XPointer: XPath++ for addressing
		XLink: hypermedia connections
	Stylesheet Attachment
	XSL: stylesheets and transforms


	A “Recommendation” since 2/1998
		The highest level for a W3C specification
	Defines the syntax/grammar
		Not any particular processing/semantics
	Schemas or DTDs define applications (poem, manual, eCommerce,...)
		All these can be parsed by generic XML, just as new words can be readily fitted into existing sentence structures
		Schemas are political as well as technical


	Disambiguate element type names
		<head><html:title>Oncataloging</html:title>… <biblio><entry id='DeRo98'> <loc:title>Navigation, Access, Control…
	Declaring prefixes
		<sec xmlns:loc="http://foo.com/mynamesp” xmlns:html='http://www.w3.org/1999/xhtml' xmlns="http://…"> <loc:title>…
		Declaration without prefix sets default
	Attributes can have namespaces
	No renaming (x:foo to y:bar)


	Let you define a document type
		What elements/attributes are defined?
		Where can they occur?
		What content is allowed?
		What datatypes are represented?
	Required for validation
	Similar to DTDs, but
		More powerful (esp. for datatyping)
		Use XML syntax


	What data in XML document “counts”?
		Elements, attributes, content
		Order and hierarchy of nodes
	Required for interoperability
		Applications must count nodes consistently
		Not whitespace inside tags
		Not which kind of quotes around attributes
	Candidate recommendation 2001-05-14
		http://www.w3.org/TR/xml-infoset


	Root: Above the document
		<?foo ?> <doc>…</doc> <!-- hi -->
	Element: Main structure
		<div n='1'>…</div>
	Text: Spans of unbroken text
	Attribute: Properties of elements
	Namespace: Prefixes/URIs
	Processing Instr: <?…?>
	Comment: <!-- … -->


	"Document Object Model"
	An API for accessing the Infoset
		Many tools use this
	Level 1 complete
		http://www.w3.org/TR/REC-DOM-Level-1
	Level 2 core complete
		http://www.w3.org/TR/DOM-Level-2-Core


	Similar to the HTML <base> element
		Useful for keeping URIs simpler and uniform.
	Applies to relative URLs
		<html> <head> <base href="http://www.example.com/"> …</head>
		<body>… <a href="fig/mosquito.png">
	The hrefs combine to make whole URI:
		http://www.example.com/fig/mosquito.png


	XML Base provides similar feature
		By a reserved attribute
		<?xml version="1.0"?>
		<doc xml:base="http://eg.org/today/">
		See <link xlink:type="simple" xlink:href="new.xml">the news</link>
		Applies to attributes & descendants
		Can be overridden on descendants
	Final REC as of 2001-06-27
		http://www.w3.org/TR/xmlbase/


	Lets documents point to stylesheets
		Based on HTML <link type='stylesheet'>
		Multiple, anywhere in XML prolog
		May point to CSS, XSL, etc.
	Example:
		<?xml-stylesheet alternate="yes" href= "mystyle.css" title="Medium" type="text/css"?>
		Equivalent of HTML: <LINK href="mystyle.css" title="Medium" rel="alternate stylesheet" type="text/css">
		REC: http://www.w3.org/TR/xml-stylesheet


Stylesheet language
	Based on ISO DSSSL and W3C CSS
2 major pieces:
	XSLT: document transformation
		Builds on XPath (more later)
		Match elements, then construct output
	XSL-FO: Formatting objects
		To actually render blocks, fonts, tables, etc.
	Hypermedia support unfinished (=CSS)
http://www.w3.org/TR/xsl/


	XPath: expressions on infoset nodes
		REC: http://www.w3.org/TR/xpath
	XPointer: XPath + ranges, in URIs
		CR: http://www.w3.org/TR/WD-xptr
	XLink: gather locations to make links
		REC: http://www.w3.org/TR/xlink/
	(XML Base)


Links from un-writable documents
	Which is most of the Web, for any person
	Perhaps the most important single feature
	->Bidirectional and multi-ended links
	->Annotations and annotation sharing
		Dynamic updates, patches, highlighting
Precise link attachment in any media
Large sets/databases of managed links
	An entirely new market for links per se
	Anyone can publish/sell their commentary


In HTML, many things are combined:
	<a href="eg.org/foo">wow</a>
Technically:
	"eg.org/foo" is a pointer (namely a URI)
	The abstract connection itself is the link
	The <a> element is a link representation
	"wow" is the local anchor
		Anchors are also called link-ends
	Data at eg.org is the remote anchor
	HTML specifies the link behavior


Describes a relationship of referenced location(s),
	To each other
	To descriptions
		XLink provides some key ones


	Locates parts of XML resources
		Even things without IDs
		Even things that aren't whole nodes
	XPointer adds (beyond XPath):
		Way to refer to point and range selections
		Way to use inside URI fragment identifiers
	TEI “extended pointer” notation plus XPath logical expressions
	Typically, a browser might load a document and scroll to/highlight the part


	Part of URIs after "#"
		Says where in document is actual target
	Separate form for each media type
		Identifiers for graphics ¹ for text
		IETF MIME definition specifies form
	HTML
		To scroll to <a name="coyote">

		http://example.com/hello.html#coyote


Bare names
	An XML "name"* finds element with that ID
	For (X)HTML compatibility
		HTML uses "NAME", not ID
Child sequences
	Stepwise down through elements: /1/4/27/2
	May start with an ID: intro/4/3/2
Full XPointers
	scheme1(args) scheme2(args)…
	For now, the only "scheme" is "xpointer"


	Provide 'scheme' mechanism
		Identify media-specific pointer types
		Allow multiple ones to co-exist
	Pointing methods for XML
		Point to ranges, sets, id's, coords…
		Point descriptively


Each media type needs pointer type
	pngRect(0,10 100,200)
	vrml(camera=1,2,3 light=4,50,500)
	map(W0°10’/ N51°30’)
	Xml(…)
Schemes label fragment identifier types
	#scheme1(args) scheme2(args)…
		Escape any extra ( ) -- tlg('^(apax')
XPointer() is the first scheme


	When a server responds to a URI, it
		Checks what media the client can handle
		Picks one of those to send
		“content negotiation”
	If a visually-impaired user clicks
		<a href="http://www.example.com/foo.gif# gif(0,0 1,1) xpointer(id(chap1))">
		The server may fall back to an XML file
		The client tries fragment identifiers left-to-right, and uses the first one that works



		root( ), id( )
		parent, self, child
		ancestor, ancestor-or-self
		descendant, descendant-or-self
		preceding-, following-sibling
		preceding, following
		attribute, namespace
		here( ), origin( )
		String-range(), range-to()


Point
	What you get by click-selection
	Gap before/after node or char
Range
	What you get by drag-selection
	From a start point to an end point
	Not generally a WF XML subtree
		May partially contain some elements:
		<p>Hello, world.</p><p>Hi, back</p>
Crucial for creating hypertext links
	How often do you click/drag exactly one entire element?


	Lets you invent your own linking elements and their meanings
		In keeping with XML approach overall
	Lets you create link databases
		Links become first-class objects in the model
	Provides some basic traversal behavior
		E.g., “Open the target in a new window”
		The rest is left to a style mechanism such as XSL


	Linking element
		Identifies, connects, and describes anchors
	Locator
		Locateses some link end (anchor)’s data
	Link end or anchor
		A data portion reachable as part of a link
	Arc
		Explicit connection between two link ends
	Resource
		Anything you can point at on the Web
	Using an arc is called Traversal


	A link identifies where its ends are
		Using some kind of locators
		URI#XPointer will be the locator for XML
		URI#scheme()scheme() in general
	A link attaches metadata to each end
		Its formal role in relation to the other ends
		A title by which to refer to it (say, in menus)
		Some traversal behaviors
		Arcs to say which traversals happen
	Link itself can also have type, other info


	Linking element itself (better, the origin() end) is one of the link’s ends


	Linking element itself isn't automatically made into one of its own resources


	Arcs specify traversal rules
	Multi-ended links may restrict travel among their endpoints
	Restrictions generic or app-specific
		Arcs enable the description of both
	An arc is a pair of roles, plus metadata
		Enables traversal between ends with the given roles
		May be multiple locators per role (useful for document assembly, multiple-choice travel)