A manager's guide to the latest hot topics

Ken Holman

Crane Softwrights Ltd.

Kars

Canada

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Abstract

No abstract was provided for this paper.

Contents

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>

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Valid XML

XML - (Valid) 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 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>

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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

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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>

Figure 1 . 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

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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

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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

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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>

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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);
}

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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

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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

Table of Contents

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)

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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>

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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

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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

Table of Contents

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:

Table of Contents

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

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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

Table of Contents

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")

Table of Contents

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>

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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

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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

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