CSI 3125, XML, page 1 An introduction to XML and friends based on these sources and inspirations: ...

CSI 3125, XML, page 1

An introduction to XML and friends

based on these sources and inspirations:

Erik T. Ray, "Learning XML", 1st ed., O’Reilly

Robert Eckstein with Michel Casabianca, "XML Pocket Reference", 2nd ed., O’Reilly

the World-Wide Web—thousands of places

Go O'Reilly!


GML and SGML

• The story begins with GML—Generalized Markup Language, invented in 1969 by Goldfarb, Mosher and Lorie from IBM as a means of allowing the text editing, formatting, and information retrieval subsystems to share documents.

• In 1978-1986 GML was substantially enlarged and then standardized by ANSI and ISO as SGML — Standard Generalized Markup Language.

• http://www.sgmlsource.com/history/sgmlhist.htm


Markup in SGML

Procedural markup

Section One

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

1

16 pt. Helvetica Bold

12 pt. Helvetica

12 pt. TimesItalic

10 pt. Palatino

12 pt. Courier

Descriptive markup

Section One

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

1

chapter head

section head

leadparagraph

paragraph

page number


HTML

• SGML is not a single markup language. It is a standard for creating markup languages.

• HTML (HyperText Markup Language) is one such language. It began modestly. In 1993, Tim Berners-Lee based his first browsing and authoring system for the Web on a handful of markup tags. The present, hugely enlarged, version is HTML 4.01—still a single language.

• HTML standards are maintained by W3C (the World-Wide Web Consortium):

– http://www.w3.org/MarkUp/

– http://www.w3.org/TR/html401/ (already 4 years old...)

http://www.w3.org/TR/html401/


XML

• XML (eXtensible Markup Language) was developed in 1996, and standardized by W3C in 1998. It is a subset of SGML.

• XML is one part of a large—and growing—family of interconnected, cooperating languages: DTD, XSL, XSTL, CSS, XPath, XPointers, XLinks, XML Schema... and that's only the beginning .

• [But what would a programmer's life be without acronyms?]

• http://www.w3.org/XML/


XML in 10 points

1. XML is for structuring data2. XML looks a bit like HTML3. XML is text, but isn't meant to be read4. XML is verbose by design5. XML is a family of technologies6. XML is new, but not that new7. XML leads HTML to XHTML8. XML is modular9. XML is the basis for RDF and the Semantic Web10. XML is license-free, platform-independent and

well-supported

http://www.w3.org/XML/1999/XML-in-10-points


XHTML

• The emergence of XML has prompted a rethinking of HTML. The new "best thing since sliced bread" is XHTML 1.0: The eXtensible HyperText Markup Language, A Reformulation of HTML 4 in XML 1.0.

• The most recent recommendation:

• August 1, 2002 : XHTML 1.0, The Extensible HyperText Markup Language (Second Edition).

– http://www.w3.org/TR/xhtml1

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

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


But what is HTML?


The structure of HTML documents

<html><head>

head elements

</head><body>

body elements

</body></html>

A quick checklist• text, images,

multimedia• resource identifiers,

URLs• element placement• fonts, colours• paragraphs, divisors• tables• forms• scripts, applets• frames

document type, title, content

descriptors, ...OPTIONAL


Links and hot links in HTML

The power of HTML lies, naturally, in HyperText links. A click on a link is a request for some content: a string, an image, a complete document, a location in a document.

<a href="http://www.google.com/"><img src="gifs/Logo_25.gif" border="0"></a>

There are two links here: an anchor (pointing to a Web location) and an image address (pointing to a local file).

XML generalizes links—see later in this presentation.


HTML up-close (1)<base href="http://www.site.uottawa.ca/~szpak/teaching/3125/"><html><head><title>CSI 3125, Fall 2002: Concepts of Programming Languages</title></head><body background="gifs/3125.gif" bgcolor=#eeeeee text=#000066 link=#0066ff vlink=#9900cc alink=#ff0000><TABLE BORDER=0 CELLSPACING=10 CELLPADDING=0 WIDTH=384><TR><TD VALIGN=TOP ALIGN=LEFT WIDTH="80%">

<p align=right><script src="Date.js"></script> <p>

Javascript


HTML up-close (2)

<center><font size=+2>Welcome to the<font color="#AA3322">CSI 3125</font>Web site!</font><br><hr width=324 size="3"><TABLE BORDER=0 CELLSPACING=10 CELLPADDING=0 WIDTH=352><TR><a href="news.html"><img src="gifs/news.gif" width=136 height=34 border=0 alt="[What's new?]"></a></TR>

seven buttons start here


HTML up-close (3)

<TR>

<TD VALIGN=CENTER ALIGN=CENTER><a href="syl3125_ToC.html"><img src="gifs/syllabus.gif" width=136 height=34 border=0 alt="[The syllabus]"></a></TD>

<TD VALIGN=CENTER ALIGN=CENTER><a href="handouts/"><img src="gifs/handouts.gif" width=136 height=34 border=0 alt="[The handouts]"></a></TD>

</TR>

</TABLE>

and two other rows of buttons


HTML up-close (4)

<hr width=324><p>The instructor's email address:<p><ahref="mailto:[email protected]">[email protected]</a> <img src="gifs/rtarrow.gif" align=bottom border=0 alt="To "><a href="http://www.site.uottawa.ca/~szpak/"><img src="gifs/home.gif" border=0 align=bottom alt="my home page"></a><p><hr width=324 size="3"><font size=-1>Updated on August 6, 2002</font><hr width=324>


HTML up-close (5)

<form method=get action="http://www.google.com/search"><table bgcolor="#dddddd"><tr><td><a href="http://www.google.com/"><img src="gifs/Logo_25.gif" border="0" alt="google"></a><input type=text name=q size=25 maxlength=256 value=""><input type=submit name=sa value="Go"></td></tr></table></form>

Google


HTML up-close (6)

<br><img src="gifs/macspin.gif" width=176 height=40 alt="[A Spinning Apple]">

</center>

</TD></TR></TABLE>

</body>

</html>

not in the picture on page

8


Back to XML...

• HTML mixes in one language two aspects of SGML: procedural markup of a document (its structure) and descriptive markup (its presentation). For example, <head> and <p> are elements of structure, while <font> and <i> describe formatting.

• In the XML world, the two aspects have been separated again. A DTD (Document Type Definition) defines the markup language, and a valid XML document must have this type. DTD has been around since the beginning of SGML. XML Schema is a new alternative, standardized in May 2001 (version 1.0).


A tiny XML document...<?xml version="1.0"?><?xml-stylesheet type="text/xsl" href="cd.xsl"?><!DOCTYPE cd SYSTEM "cd.dtd">

<cd type="single"> <title>Revolver, top two</title>

<band>The Beatles</band>

<track> <song>Eleanor Rigby</song> <time>2:45</time> </track>

<track> <song author="Paul and John"> For No One </song> </track></cd>

formatting(discussed

later)

structure

cd.xml


... its DTD...



<!ELEMENT cd (title, band, track+)><!ATTLIST cd type (single | regular) #REQUIRED><!ELEMENT title (#PCDATA)><!ELEMENT band (#PCDATA)><!ELEMENT track (song, time?)><!ELEMENT song (#PCDATA)><!ELEMENT time (#PCDATA)><!ATTLIST song author CDATA "Paul">

cd.dtd


... and its validation

Three easy steps to validate an XML document:

– Connect (ssh) to the Linux machine site2.

– Have the document and its DTD in the same directory.

– Invoke the XML validator xmllint.

szpak|site2-1: ls cd.*

cd.dtd cd.xml

szpak|site2-2: xmllint --valid --noout cd.xml

szpak|site2-3:

(In this course, you will get to validate a few XML documents. )


Elements and attributes

Empty elements

<name attr1 = "val1" attr2 = "val2" ... />

<price amount="11.98" />

Container elements

<name attr1 = "val1" attr2 = "val2" ... >

content

</name>

<song author="Paul and John">

For No One

</song>


Snippets of DTD syntax

<!ELEMENT cd (title, band, track+)>Elements of cd in this order, with one or more track.<!ELEMENT title (#PCDATA)>Parsed-character data: entity references resolved.<!ELEMENT track (song, time?)>time is optional.<!ATTLIST cd type (single | regular) #REQUIRED>One of these two values must be present.<!ATTLIST song author CDATA "Paul">Character data, default is Paul.<!ATTLIST song lyricist NMTOKEN #IMPLIED>An identifier (more or less), optional, no default.


XML is stricter than HTML

• XML is case-sensitive.

• Attribute values must be in quotation marks.

• A container (non-empty) element must have an opening and closing tag.

• An empty element must have a final slash.

• Tags must be nested correctly (see next page).

• Whitespace in element content is preserved.

You can think of an XML document as an HTML document with customized tags (and much more — you will soon see a little of that), but keep in mind that XML is a lot more picky than HTML.


A document is a tree

<cd type="single"> <title>Revolver, top two</title> <band>The Beatles</band> <track> <song>Eleanor Rigby</song> <time>2:45</time> </track> <track> <song author="Paul and John"> For No One </song> </track></cd>


Entities in HTML

HTML allows us to refer to hard-to-type characters using the & convention. Examples:

non-breaking space

ë ë

a a

à à

é é

This is significantly extended in XML. An entity is a "placeholder for content"; it can denote anything, even a fragment of markup. Entities are resolved, or replaced, quite like macros.


Entities in XML (1)

We have general entities (either defined locally, or external and publicly available) and parameter entities used in DTDs. We also have predefined character entities, among them five necessary to avoid confusion with markup syntax:

& &

' '

> >

< <

" "


Entities in XML (2)

<!ENTITY % basiccontent "(#PCDATA)">

<!ELEMENT cd (title, band, track+)><!ATTLIST cd type (single | regular) #REQUIRED><!ELEMENT title %basiccontent;><!ELEMENT band %basiccontent;><!ELEMENT track (song, time?)><!ELEMENT song %basiccontent;><!ELEMENT time %basiccontent;><!ATTLIST song author CDATA "Paul">

cd3.dtd

references

parameterentity


Entities in XML (3)<?xml version="1.0"?><?xml-stylesheet type="text/xsl"

href="cd3.xsl"?><!DOCTYPE cd SYSTEM "cd3.dtd" [ <!ENTITY favourite "For No One"> <!ENTITY bestever "The Beatles"> ] ><cd type="single"> <title>Revolver, top two</title> <band>&bestever;</band> <track> <song>Eleanor Rigby</song> <time>2:45</time> </track> <track> <song author="Paul and John"> &favourite; </song> </track></cd> cd3.xml

local entities

reference

reference


The stylesheet philosophy

• The presentation aspect of XML documents is handled in an elegant, general manner: by structure transformation. A stylesheet defines templates that can transform elements of a valid XML document into another structure. for example, into HTML.

• Access to elements is made easy by XPath, a rich language that allows us to move around a document and apply a variety of conditions. (We will see no XPath here—no time. )


A simplistic stylesheet (1)

<?xml version="1.0"?><xsl:stylesheet id="cds" version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output method="html"/><xsl:template match="cd"> <html> <body> <xsl:apply-templates/> </body> </html></xsl:template>

cd.xls

<cd type="single">......</cd>

<html> <body> ------ </body></html>

This is an XML document!



<xsl:template match="title"> <h3><xsl:apply-templates/></h3> <br /><br /></xsl:template>

<xsl:template match="band"> <h4><xsl:apply-templates/></h4> <hr /></xsl:template>

<xsl:template match="track"> <p><xsl:apply-templates/></p></xsl:template>

<band>....</band>

<h4>----</h4><hr />

cd.xls



<xsl:template match="track"> <p><xsl:apply-templates/></p></xsl:template>

<xsl:template match="song"> <b><xsl:apply-templates/></b> <br /></xsl:template>

<xsl:template match="time"> <i><xsl:apply-templates/></i> <br /></xsl:template>

</xsl:stylesheet>

<song>...</song>

<b>---</b><br />

cd.xls


Links in XML, on one example

target is any local or public resource.

showhow is new, embed or replace. (In HTML: open a new window, embed a graphic, follow a link in the same window.)

showwhen is onLoad or onRequest.

/>if element empty

<elementname xlink:type = "simple" xlink:href = "target" xlink:show = "showhow" xlink:actuate = "showwhen">some content</elementname>


A larger example: checkbook

This example, due to Erik T. Ray ("Learning XML"), can be found on the course Web site:

checkbook.dtd

checkbook.xml

checkbook.xsl

Visit

http://www.site.uottawa.ca/~szpak/teaching/3125/handouts/other/perl_xml.html

and enjoy as best you can.

And now...


In another course • XML Schema (much more control of the form of data

than DTDs)

• CSS (Cascading Style Sheets—old but useful)

• XSL—lots of details

• Namespaces

• XSLT (Extensible Style Language for Transformations)

• XPath (locating objects in documents)

• XLink, XPointer (links between documents)

• XML tools (parsers, syntax checkers, validators, tree processors, etc.)

• Standards, public documents, Web resources


XML validation

Three easy steps to validate an XML document:

• ssh to the Linux machine site2.

• Have the document and its DTD in the same directory.

• Invoke the XML validator xmlvalid.

% ls cd.*

cd.dtd cd.xml

% xmlvalid cd.xml

cd.xml is valid

(there will be error

messages if not )

XML/XSL tools in Linux


XML parsing

Another XML tool in Linux:

• ssh to the Linux machine site2.

• Have the document and its DTD in the same directory.

• Invoke the XML processor xmllint.

% ls cd.*cd.dtd cd.xml% xmllint cd.xml(there will be error messages if not valid)

xmllint has many options.To find out about them, type:% xmllint

For even more, type:% man xmllint



You can also see some simple facts about a valid XML document. The Perl program dbstat, posted on the course Web site, does it for us. Remember to make it executable.

% dbstat cd.xml

Node frequency: 2 PI nodes 8 element nodes 0 comment nodes 2 attribute nodes 19 text nodes 0 CDMS nodes

32 total nodes

Element frequency: 1 <band> 1 <cd> 2 <song> 1 <time> 1 <title> 2 <track>

XML statistics



Then there is an XSL processor xsltproc, also with many options. To see them, type:

% xsltproc

For even more, type:

% man xsltproc

You can parse (and validate) an XSL file:

% xsltproc cd.xsl

(there will be error messages if not valid)

XSL processing



You can also run the XSL processor on an XML file, according to a stylesheet, and get the result — for example, an HTML file.

% xsltproc cd.xml<html><body> <h3>Revolver, top two</h3><br><br>

<h4>The Beatles</h4><hr>

<p> <b>Eleanor Rigby</b><br> <i>2:45</i><br> </p>

<p> <b> For No One </b><br> </p></body></html>

XSL processing

Date post:	04-Jan-2016
Category:	Documents
Upload:	dorthy-freeman
View:	223 times
Download:	0 times

CSI 3125, XML, page 1 An introduction to XML and friends based on these sources and inspirations: ...

Documents