	XML crosses the chasm		Table of contents		Indexes		Using the technology

A manager's guide to the latest hot topics

Holman, Ken

Ken Holman

Chief Technology Officer

Canada

Crane Softwrights Ltd.

Kars

Ontario

Crane Softwrights Ltd., Box 266
Kars Ontario Canada web site: www.CraneSoftwrights.com

Biography

G. Ken Holman — Mr. G. Ken Holman is the Chief Technology Officer for Crane Softwrights Ltd., a Canadian corporation offering OmniMark programming, DSSSL and XSL/XSLT language training, and general SGML and XML related computer systems analysis services to international customers. Mr. Holman is the current Canadian chair of the ISO subcommittee responsible for the SGML family of standards, an invited expert to the W3C, the author of "Practical Transformation Using XSLT and XPath (XSL Transformations and the XML Path Language)" (ISBN 1-894049-04-7), and has often been a speaker at related conferences. Prior to establishing Crane, Mr. Holman spent over 13 years in a software development and consulting services company working in the NAPLPS and the SGML industries.

Well-formed XML

XML - (Well-formed) Extensible Markup Language

http://www.w3.org/XML

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

http://www.w3.org/XML/xml-19980210-errata

http://www.xml.com/axml/axml.html - annotated version

a syntax for structured information

rules for properly nested hierarchically organized information

identifies information with markup that can be accessed

the model of the document is implicit in the hierarchy of the data

enables custom marked up information to be served, received, and processed on the Web in the way that is now possible with HTML

designed for ease of implementation and for interoperability with both SGML and HTML

A well-formed instance:

<?xml version="1.0"?>
<weather>
<current>
<temp scale="F">72</temp>
<pressure>1005</pressure>
<humidity>43</humidity>
</current>
<min>
<temp scale="F">65</temp>
<pressure>998</pressure>
<humidity>38</humidity>
</min>
<max>
<temp scale="F">78</temp>
<pressure>1010</pressure>
<humidity>43</humidity>
</max>
</weather>

Valid XML

XML - (Valid) Extensible Markup Language

http://www.xml.com/axml/axml.html

http://www.xml.com/axml/axml.html - annotated version

a syntax for specification of a model of structured information

the model of the document is explicit in the set of declarations

enables tools to constrain the creation of information to a given model

enables tools to confirm information conforms to a given model

is focused on the hierarchical structure (with no content typing)

A valid instance:

<?xml version="1.0"?>
<!DOCTYPE weather [
<!ELEMENT weather  ( current, ( min, max )? )>
<!ELEMENT current  ( temp, pressure, humidity )>
<!ELEMENT min      ( temp, pressure, humidity )>
<!ELEMENT max      ( temp, pressure, humidity )>
<!ELEMENT temp     ( #PCDATA )>
<!ATTLIST temp     scale ( C | F ) #REQUIRED>
<!ELEMENT pressure ( #PCDATA )>
<!ELEMENT humidity ( #PCDATA )>
]>
<weather>
<current>
<temp scale="F">72</temp>
<pressure>1005</pressure>
<humidity>43</humidity>
</current>
<min>
<temp scale="F">65</temp>
<pressure>998</pressure>
<humidity>38</humidity>
</min>
<max>
<temp scale="F">78</temp>
<pressure>1010</pressure>
<humidity>43</humidity>
</max>
</weather>

XML Schema

http://www.w3.org/TR/xmlschema-1/ - Structures

http://www.w3.org/TR/xmlschema-2/ - Datatypes

a vocabulary for specifying schemata for different vocabularies

defines and describes classes of XML documents

defines structural, syntactic and value constraints and relationships

elements

attributes

contents

datatypes

documents meaning and usage

supplies default values for attributes and elements

XML instance syntax

schema document contains representations of schema components

hierarchical constructs

can be embedded within a document instance

need not be a standalone document

can be created with standard XML instance editing tools

unlike Document Type Definitions

Does not attempt to provide all facilities

some applications must still provide customized semantic validation

Part 1: Structures

nature of XML schemas and component parts

application of XML schemas to XML documents

defines hierarchical relationships of constituent members

type definition hierarchies

Part 2: Datatypes

nature of content of attributes and text

e.g.: integer, date, string, boolean, float, double, decimal, etc.

atomic and aggregate types

primitive and generated types

built-in and user-generated types

a language for use with XML Schema and other future XML Recommendations

perhaps including XSL and RDF

high degree of type checking

ensures robustness in information interchange

extensible to custom types

stand-alone

derived from standardized types

attribute content and element content

Schematron

http://www.ascc.net/xml/resource/schematron/schematron.html

developed by Rick Jelliffe, Academia Sinica Computing Centre

a data assertion validation language useful for validating information against business rules

an approach to validating an instance unlike using schemata

a schema defines a grammar

the validating process checks the instance against the grammar

parent/child relationships specified in content models

a set of assertions describes expected content of an instance

the Schematron checks the instance against the set of assertions

arbitrary relationships (e.g. cousin, grandparent, etc.) can be specified

encoding of business rules related to structural integrity of the instance

assertions are made using XPath expressions

provides for coupling expressions

assertions can rely on other assertions being true or false

unable to be expressed in a grammar-based schema

A valid XML instance needing Schematron for business rule validation:

<?xml version="1.0"?>
<!DOCTYPE thing [
<!ELEMENT thing ( a | b )>
<!ATTLIST thing content ( a | b ) #REQUIRED>
<!ELEMENT a (#PCDATA)>
<!ELEMENT b (#PCDATA)>
]><thing content="a"><b>test</b></thing>

Using a Schematron:

Of note:

there are a number of different Schematrons providing different styles of reports

the output of using Schematron is a validation/reporting stylesheet

the stylesheet can be run on any number of instances without regenerating

Namespaces

Vocabulary distinction

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

http://www.megginson.com/docs/namespaces/namespace-questions.html

specifies a simple method for qualifying element and attribute names used in XML documents

allows the same element type name to be used from different vocabularies in a given document

consider two vocabularies each defining the element type named " <set> ", each with very different semantics

in SVG (Scalable Vector Graphics) the element <set> refers to setting a value within the scope of contained markup

in MathML (Math Markup Language) <set> refers to a collection of constructs treated as a set

any document needing to mix elements from the two vocabularies may need to use the same named

without namespaces an application cannot distinguish which construct is being used

a namespace prefix differentiates the element type name suffix in an instance

<svg:set>

<math:set>

composite name lexically parses as an XML name

the use of the colon is defined by the namespaces recommendation

also used to uniquely distinguish identification labels in some Recommendations

e.g.: customized sort scheme label

URI value association

associates element type name prefixes with Universal Resource Identifier (URI) references whether or not any kind of resource exists at the URI

examples:

xmlns:svg="http://www.w3.org/2000/svg-20000303-stylable"

xmlns:math="http://www.w3.org/1998/Math/MathML"

URI domain ownership under auspices of established organization

URI conflicts avoided if rules followed

explicitly does not expect nor require to de-reference any kind of information from the given URI

note that the Resource Description Framework (RDF) recommendation does have a convention of looking to the URI for information, though this is outside the scope of the Namespaces recommendation

according to the recommendation, the URI is only used to disambiguate otherwise identical unqualified members of different vocabularies

The choice of the prefix is arbitrary and can be any lexically valid name

the name need not be consistent with the use (though this helps legibility)

the name is never a mandatory aspect of any Recommendation

the prefix is discarded by the XML namespace-aware processor along the lines of:

<{http://www.w3.org/2000/svg-20000303-stylable}set>

<{http://www.w3.org/1998/Math/MathML}set>

the above use of " { " and " } " are for example purposes only

note how the " / " characters of the URI would be unacceptable given the lexical rules of names, thus, the URI could never be used directly in the tags of an XML document

the prefix is merely a syntactic shortcut preventing the need to specify long distinguishing strings

Extensible HyperText Markup Language (XHTML)

http://www.w3.org/TR/xhtml1

a reformulation of HTML using XML 1.0

reproduces, subsets and extends HTML 4 vocabulary

XML-conforming and operates in HTML 4 conforming user agents

XHTML files are acceptable input to XML processing tools

stylesheets

applications

Cascading Stylesheets (CSS)

http://www.w3.org/TR/REC-CSS1

http://www.w3.org/TR/REC-CSS2

formatting property assignment for web documents (HTML and XML)

no document manipulation capabilities

only ornamentation of the document tree

attaching stylistic information to nodes

simple prefixing and suffixing of nodes with text

control of whitespace around information

overlapping and transparent rectangular regions

multiple media type support

character display presentation properties

tabular presentation properties

aural presentation properties for visually impaired browsing

disabled users

mobile users

doesn't (shouldn't) interfere with legacy browsers not supporting CSS

working group producing a common formatting model for web documents

Example HTML Specification:

<html>
<head>
<Title>Test</title>
<style type="text/css">
H1    { color: green; text-align: right }
.info { color: red }
</style>
</head>
<body>
<h1>Test File</h1>
<p class="info">This is a test</p>
</body>
</html>

Example XML Specification:

The file samp.css :

EMPH        { color: red; display: inline; font-style:italic }
PARA, TITLE { font-family: arial, sans-serif; display: block }
TITLE       { font-weight: bold }
TITLE EMPH  { color: blue }

for the file samp.xml :

<?xml version="1.0"?>
<?xml-stylesheet type="text/css" href="samp.css"?>
<INFO>
<TITLE>Title with <EMPH>emphasis</EMPH></TITLE>
<P>This is a paragraph.</P>
<P>This has <EMPH>emphasis</EMPH>.</P>
<P>Last paragraph</P>
</INFO>

Document Object Model (DOM)

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

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

a tree-oriented platform- and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure and style of documents

a programmatic interface for XML and HTML

a model of objects for XML and HTML

a standard interface for manipulating the objects

built on three layers of functionality

Core

fundamental interfaces

XML extended interfaces

HTML extended interfaces

an agreed-upon fence between a programmer and a vendor

programmers write to the standard interface without knowledge of vendor implementation

vendors support the standard interface to their internal data structures without needing to share proprietary information

Example Principles:

the document is a hierarchy of nodes

a node can be in an ordered node list

a node can be named in an unordered set

the interface implementation can build node trees, lists and sets from documents

a programmer can manipulate node trees, lists and sets from program control

Example Interface Definition:

interface Attr : Node {
readonly attribute  DOMString            name;
readonly attribute  boolean              specified;
attribute  DOMString            value;
};

the name of the attribute

the indication of the attribute being specified (true) or defaulted (false)

the attribute's value (obtainable and settable)

Example Language Binding (Java):

public interface Attr extends Node {
public String             getName();
public boolean            getSpecified();
public String             getValue();
public void               setValue(String value);
}

Simple API for XML (SAX)

http://www.megginson.com/SAX

developed entirely within the user community under the direction of David Megginson, using the XML-DEV mail list

a stream-oriented platform- and language-independent specification of functions that allows programs to process XML information

classical event-handling scheme

XML constructs trigger events defined by the interface

program routines handle events to implement application-specific processing

no need to maintain the XML hierarchy in memory

an application can use a SAX interface to build an XML hierarchy from a stream

SAX 2 currently under development

Multiple implementations freely available:

Java

Python

COM

Perl

C++

many XML processors include a SAX interface to the XML information

Example of events defined in SAX:

start of document

start of element

characters

end of element

end of document

Simple Object Access Protocol (SOAP)

http://search.ietf.org/internet-drafts/draft-box-http-soap-01.txt

defines a remote procedure call (RPC) mechanism using XML syntax

implements client-server interaction across a network

a standard object invocation protocol built on Internet standards

HTTP transport layer

XML for encoding

invocation requests

responses

extensible protocol

extensible payload format

incorporates SOAP vocabulary for enveloping information

incorporates user vocabularies for payload

simple datatypes for values based on XML Schema Datatypes

includes arrays, compound and other types to the simple types

XML Path language (XPath)

Addressing identifies a hierarchical position or positions

common semantics and syntax for addressing

functionality required by both XSLT and XPointer

a compact non-XML syntax

for use in attribute values of XML documents

select="id('start')//question[@answer='y']"

select all question elements whose answer attribute is " y " that are descendants of the element in the current document whose unique identifier is " start "

A single W3C recommendation

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

a data model for representing an XML document as a node tree

a mechanism for addressing information found in the document node tree

an expression language for the manipulation of boolean, numeric, string and node values

a core upon which extended functionality specific to each of XSLT and XPointer is added

XPath is not a query language

one aspect of querying is addressing information that needs to be found

other aspects of querying involve working with the information that is addressed before returning a result to the requestor

XPath is used only to address components of an XML instance, and in and of itself does not provide any traditional query capabilities (though hopefully would be considered as the addressing scheme by those defining such capabilities)

XSL and XSLT

XSL - Extensible Style Language

XSLT - XSL Transformations

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

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

two separate vocabularies of XML

transformation vocabulary to manipulate input documents into desired output structure

has a processing model makes it possible to script non-linear traversal of information (identical to the DSSSL processing model and unlike the CSS processing model)

uses XPath as a base expression language

added extensions specifically for linking

can transform XML into XML, HTML, HTML+CSS, HTML+DOM+CSS, simple text

formatting vocabulary to express desired semantics for presentation

adopts style semantics from already-established standards

DSSSL (Document Style and Semantics Specification Language - ISO/IEC-10179)

CSS (Cascading Style Sheets - W3C)

Consider the source file being processed includes a <note> element

must be rendered in italics and boldface, between two horizontal lines, as a paragraph on its own, prefixed by "Note: "

To produce formatting objects according to XML lexical and syntax rules:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/XSL/Transform/1.0"
xmlns:fo="http://www.w3.org/XSL/Format/1.0">

<xsl:import href="main.xsl"/>

<xsl:template match="note">
<fo:display-rule/>
<fo:block font-posture="italic" font-weight="bold">
<xsl:text>Note: </xsl:text>
<xsl:apply-templates/>
</fo:block>
<fo:display-rule/>
</xsl:template>

</xsl:stylesheet>

To produce HTML according to SGML lexical and syntax conventions:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/XSL/Transform/1.0">

<xsl:output method="html"/>

<xsl:import href="main.xsl"/>

<xsl:template match="note">
<hr/>
<p><i><b>
<xsl:text>Note: </xsl:text>
<xsl:apply-templates/>
</b></i></p>
<hr/>
</xsl:template>

</xsl:stylesheet>

Stylesheet association

Relating documents to their stylesheets

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

associating one or more stylesheets with a given XML document

same pseudo-attributes and semantics as in the HTML 4.0 recommendation elements:

<LINK REL="stylesheet">

<LINK REL="alternate stylesheet">

Ancillary markup

not part of the structural markup of an instance, thus it is marked up using a processing instruction rather than first-class (declared or declarable in a document model) markup

Typical examples of use:

<?xml-stylesheet href="fancy.xsl" type="text/xsl"?>
<?xml-stylesheet href="normal.css" type="text/css"?>

Less typical examples provided for by the design:

<?xml-stylesheet alternate="yes" title="small"
href="small.xsl" type="text/xsl"?>

provide the processor with an alternate stylesheet if some external stimulus triggers it by name

<?xml-stylesheet href="#style1" type="text/xsl"?>

instruct the processor to find the stylesheet embedded in the source document at the named location

XML pointing and linking languages (XPointer and XLink)

Linking describes a relationship:

the association of information as defined by two components

the addresses of what are being associated

the essence of the association

Two W3C recommendations:

designed to work together to fulfill these two objectives

XPointer

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

defines constructs that support addressing into the internal structure of XML documents

specific reference to elements, character strings and other parts of XML documents

address ranges or individual nodes

extends what is provided in XPath as a core

addressing expressions in URI (Universal Resource Identifier) references as fragment identifiers

independent of use as either a link destination or some other application-specific purpose

Two W3C recommendations (cont.):

XLink

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

defines constructs that support describing the links between addressed information

asserts relationships to exist between two or more data objects or portions of data objects

simple unidirectional hyperlinks

more sophisticated multi-ended and typed links

includes semantic and behavior attributes

some believe these behaviors should be entirely layered upon generic semantic information as happens in formatting

Rich heritage

is based on concepts successfully developed and used in

TEI (Text Encoding Initiative)

HyTime (Hypermedia and Time-based Structuring Language - ISO/IEC-10744)

First-class markup

constructs are not ancillary to the markup of the document

linking information is marked up using elements and attributes

unlike an ancillary construct such as stylesheet association (using a processing instruction)

the linking of two or more pieces of information is part of the essence of the information being described

XML Topic Maps

http://www.infoloom.com/topmap.htm

http://www.TopicMaps.com

http://www.TopicMap.com

an architecture for defining notations for structuring information resources by defining topics and relationships between topics

occurrences

groupings of addressable information objects

associations

relationships between topics

facets

property/value pairs to information objects and components

scopes

limitations on what can be associated (for consistency and appropriateness)

based on ISO/IEC 13250:1999 Topic Maps

itself based on ISO/IEC 10744:1997 HyTime

being recast in XML

will base locations on XPointer

Co-existing models of knowledge domains

ideal for navigation by conceptual subjects and themes

used to relate information found in a corpus of numerous resources of numerous types

oriented to a human as the end user of the information

ideal for indexes, glossaries, thesauri, general finding aids

typically ancillary to the corpus itself

applied from "above" the information set rather than from "within" the information set

information set is untouched by the application of a topic map

Architecture based:

information modelers define vocabularies derived from the Topic Map architecture

navigation tools can accommodate arbitrary vocabularies by acting on Topic Map base architecture

A navigation description document:

Resource Description Framework (RDF)

http://www.w3.org/RDF

http://www.w3.org/TR/PR-rdf-schema

http://www.w3.org/TR/REC-rdf-syntax

general treatment of metadata (information about information)

oriented to a computer as the end user of the information

enables automated processing of web resources

searching

cataloguing

hierarchical site maps

an RDF data model resembles an entity-relationship diagram

classes and properties

schema-specification vocabulary in XML syntax

user defines resource description language as an application-specific schema

attributes and relationships of items on the web

resources and their properties

XML Query

http://www.w3.org/TR/xmlquery-req

create a data model for XML documents

based on the XML Information Set

includes support for Namespaces

create a set of query operators against the data model

for a fixed collection of documents

for a single document

for a collection of simple and complex values

independent of any evaluation strategy

completely declarative

supports simple and complex types from XML Schema Datatypes

supports references within and between XML documents

supports real and virtual documents

can act on transient result of transformation not present in a static form

XML Signature

http://www.w3.org/TR/xmldsig-requirements

http://www.w3.org/TR/xmldsig-core/

a XML syntax used for creating and representing signatures on digital content

procedures for computing and verifying such signatures

methods of referencing collections of resources

algorithms

keying information and management

flexible signing methods

enveloped signatures for content from one or more resources in the same or separate XML documents

detached signatures for data outside of the document containing the signature

basic signature services

data integrity ("this data is unchanged and whole")

authentication ("this data came from me")

non-repudiation ("this data came from you")

Scalable Vector Graphics (SVG)

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

http://www.svgcentral.com/

a vocabulary for representing two-dimensional graphics

common semantics with differing application syntax

that can be exchanged

final-use rendering properties embedded in the instance

guarantees interoperability

explicitly does not include facilities for embedding stylesheets or style declaration blocks

XML alternative for graphic interchange formats such as Encapsulated PostScript (EPS)

that can be styled

final-use rendering properties are not embedded in the instance

arbitrary styling languages can influence presentation

external stylesheets

internal stylesheets

embedded style declaration blocks

cascade of styling properties

using DOM and scripting allows an existing instance of SVG to be manipulated and dynamically refreshed

can be the result vocabulary of the output of applying XSL Transformations to XML sources

Basic types of constructs

geometric vector

image

text

Unlimited application areas:

charting

information visualization

cartography

Consider a simple example of polygons:

<?xml version="1.0"?>
<svg width="175" height="145" >
<g style="stroke:black; fill:black" >
<polygon points="  5, 50,  5, 81, 12, 64" />
<polygon points="  5, 45, 41,116, 41, 73" />
<polygon points=" 44, 76, 44,119, 61,115" />
<polygon points=" 46, 73, 75,140,105, 73" />
</g>
<g stroke="black" fill="black">
<polygon points="107, 76,106,119, 89,115" />
<polygon points="144, 45,109,116,109, 73" />
<polygon points="145, 41,167,  4,109, 71" />
<polygon points=" 66, 72, 75, 63, 84, 72" />
</g>
</svg>

Mathematical Markup Language (MathML)

http://www.w3.org/TR/REC-MathML

http://www.w3.org/TR/MathML2

a vocabulary for describing mathematical notation

captures structure/presentation

28 element types

traditional math constructors

basic kinds of symbols

expression-building structures

captures intended semantics

75 element types

encoding of underlying mathematical constructs

accommodates ambiguous presentation of differing concepts

may be processed and evaluated

supports (though not necessarily completely) arithmetic, algebra, logic and relations, calculus, set theory, sequences and series, trigonometry, statistics, linear algebra

well-defined interaction between presentation and semantics

catalogue of entities for extended characters

Wireless Application Profile (WAP)

http://www.wapforum.org/

a vocabulary targeted for information delivery and presentation for mobile applications

Wireless Markup Language (WML)

derived from HTML

includes WML scripting language

presentation controls optimized for smalls screens

scalable from line displays to graphical displays

navigation controls facilitate one-hand usage

security facilities

client-server architecture

simple, thin user agent (micro-browser)

WAP Gateway manages and directs information traffic


	XML crosses the chasm		Table of contents		Indexes		Using the technology