DIG 3134 – Internet Software Design

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DIG 3134 – Internet Software Design

Lecture 17 - XML:

eXtensible Markup LanguageJ. Michael Moshell

University of Central Florida

Original image* by Moshell et al .

Imagery is fromWikimedia except where marked with *. Licensing is listed.

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Purposes of XML:

• Make data more easily used• Make data last longer (across generations of technology)

Strategy of XML:

• Provide a basis for creating 'dialects' for special purposes- Thus, XML is a meta-language

• Provide tools you can use, rather than re-invent

Structure of XML:

• Inject <tags> into text files

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XML Syntax:

Declaration:

Nested elements:

<?xml version="1.0" encoding="UTF-8">

<student> <person>

<last-name>Wilson</last-name><first-name>Henry</first-name><address>122 Smith Road</address>

</person> <major>Digital Media</major> <transcript>

<course semester="Fall 06">DIG 4921c</course><course semester="Fall 06">DIG 4526 </course>

</transcript></student>

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XML Syntax:

Declaration:

Nested elements:


<student> <person>





content

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XML Syntax:

Declaration:

Nested elements:


<student> <person>





attribute

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XML Syntax:

Declaration:

Nested elements:


<student> <person>




</transcript></student> valuename

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XML Syntax:

Declaration:

Nested elements:


<student> <person>




</transcript></student> valuename

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Real World Example:

E-commerce (Euro processing) in a PHP application

function sendResponse($status, $statusmessage, $neworderid, $batchid){ echo '<?xml version="1.0" encoding="utf-8"?>'; echo "<responsemessage>"; echo "<status>".$status."</status>"; echo "<statusmessage>".$statusmessage."</statusmessage>"; echo "<neworderid>".$neworderid."</neworderid>"; echo "<batchid>".$batchid."</batchid>"; echo "</responsemessage>";}

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This raises a Question;

Nested elements:<student> <person>





How does one represent the 'grammar' ofan element ... e. g. A transcript will consist of

zero or more courses.

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This raises a Question;

Nested elements:<student> <person>



<course semester="Fall 06">DIG 4921c</course><course semester="Fall 06">DIG 4526 </course><gradepoint>3.62</gradepoint>


How does one represent the 'grammar' ofan element ... e. g. A transcript will consist of

zero or more courses.

This will be done via a SCHEMA.

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Two kinds of "grammaticality"

Well-formed:

• one ROOT ELEMENT - e. g. <student> ... </student> per document

• all non-empty elements are delimited with start & end tags.

• Empty elements are delimited properly

- intentionally empty placemarkers: <thisway />

- temporarily empty placemarkers: <likethis></likethis>

• All attribute values are quoted.

• Tags do not overlap.

• Document complies to its character set definition.

1. Well-formedness (standard XML)2. Validity (based on a schema)

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Schemas represent a particular

We're not going to explore Schemas in this lecture.

But we do have ANOTHER issue to mention:

NAMESPACES ... consider this piece of XML:

<student> <person>


</person> <major>Digital Media</major>

"language" subset of XML

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Namespaces

What's a 'major'? What are the legal values? What is its relationship to a particular university? Does it have a relationship to any national or world standards?

<student> <person>

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Namespaces

What's a 'major'? What are the legal values? What is its relationship to a particular university? Does it have a relationship to any national or world standards?

<student> <person>

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Namespaces

At the listed "URI" (similar to a URL) would be founda description of what kinds of things can be put intothe 'major' field.

This allows people to establish and share standards.(There is no such thing as example.org ... it's a placeholder)

<student> <person>


</person> <major xmlns="http://example.org/academicmajor">

Digital Media</major>

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Namespaces: Another example

<root>

<h:table xmlns:h="http://www.w3.org/TR/html4/">

<h:tr>

<h:td>Apples</h:td>

<h:td>Bananas</h:td>

</h:tr>

</h:table>

<f:table xmlns:f="http://www.w3schools.com/furniture">

<f:name>African Coffee Table</f:name>

<f:width>80</f:width>

<f:length>120</f:length>

</f:table>

</root>

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XML into PHP: Start simple...

<person>

<lastname>Wilson</lastname>

<firstname>Henry</firstname>

<address>122 Smith Road</address>

</person>

$xml = simplexml_load_file($filename);print "Raw xml:";

print_r($xml);

print " ";

Then I ran this code to suck it into PHP and look at it:

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And the results: <person>




</person>

Raw xml:SimpleXMLElement Object (

[lastname] => Wilson

[firstname] => Henry

[address] => 122 Smith Road )

The resulting object looked like this ( via print_r )

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To access some piece (e. g. lastname): <person>




</person>

$lastname=$xml->lastname; // $xml is an objectprint "ln=$lastname ";

print " ";

And the output was

ln=Wilson

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A more complex record:

<student>

<person>




</person>

<transcript>

<course level='undergrad'>

<title>DIG 3134</title>

<semester>Fall 2011</semester>

<grade>A</grade>

</course>

<course>

<title>DIG 3353</title>

<semester>Spring 2011</semester>

<grade>C</grade>

</course>

</transcript>

</student> see xample.php (as .txt)

The Battleship XML This example represents two ships for the 'black' team.<ocean>

<ship number='1'>

<x>A</x> <y>1</y>

<orientation>horizontal</orientation> <type>black</type>

</ship>

<ship number='2'>

<x>H</x> <y>1</y>

<orientation>vertical</orientation> <type>black</type>

</ship>

</ocean>

The Battleship XML This example represents two ships for the 'black' team.<ocean>

<ship number='1'>

<x>A</x> <y>1</y>

<orientation>horizontal</orientation> <type>black</type>

</ship>

<ship number='2'>

<x>H</x> <y>1</y>

<orientation>vertical</orientation> <type>black</type>

</ship>

</ocean>

Attribute-

Value

pair

How do we read XML?

$xml=simplexml_load_file($shipfilename);

But what is now in the variable '$xml' ?

To find out, we use the print_r function.

print_r ($xml); -- what do we get?

SimpleXMLElement Object ( [ship] => Array ( [0] =>

SimpleXMLElement Object ( [@attributes] => Array

( [number] => 1 ) [x] => A [y] => 1 [orientation] => horizontal [type]

=> black ) [1] => SimpleXMLElement Object

( [@attributes] => Array ( [number] => 2 ) [x] => H [y] => 1

[orientation] => vertical [type] => black ) ) )

AMess!

SimpleXMLElement Object (

[ship] => Array (

[0] => SimpleXMLElement Object (

[@attributes] => Array ( [number] => 1 )

[x] => A

[y] => 1

[orientation] => horizontal

[type] => black )



[x] => H [y] => 1

[orientation] => vertical

[type] => black ) ) )

Prettyprint it:

If you "View Source" on a print_r output,

you will see the prettyprinted version.

This is easy with Firefox (Command-U).

Prettyprint it:

Getting at the data

$ships=$xml->ship;

foreach ($ships as $ship)

{

$xc=$ship->x; // x-character (like 'A')

$xlo=(ord(strtoupper($xc))-64); // get it?

$ylo=$ship->y; // y-smallest number (like 1)

$orientation=$ship->orientation; // like 'vertical'

// more to come

Checking the data

$xc=$ship->x; // x-character (like 'A')




logprint("xc=$xc,ylo=$ylo,or=$orientation",5);

output: xc=A, ylo=1, or=horizontal

Ominous storm clouds$xc=$ship->x; // x-character (like 'A')




logprint("xc=$xc,ylo=$ylo,or=$orientation",5);

output: xc=A, ylo=1, or=horizontal

everything looks normal and reasonable .. BUT ...

(cue the scary organ music….) TROUBLE ahead!

Meanwhile … getting at the data

$shipattributes=$ship->attributes( ); // eh?

// The attributes of the <ship> element are

// returned by a special built-in method,

// in the form of an array. We saw:

[ship] => Array (



// so, to 'peel' the info, we access an array element.

$shipnumber=$shipattributes['number'];

Continuing the story …

$ships=$xml->ship;

foreach ($ships as $ship)

{ // … further down the foreach loop:

$type=$ship->type;

if ($type=='black') $fillcolor=BLACK;

else $fillcolor=GOLD;

if ($orientation=='horizontal')

{ // and we get ready to draw a ship into $Grid

Then something WEIRD happened

for ($x=$xlo; $x<=$xlo+4; $x++)

{

$Grid[$x][$y]=$fillcolor;

And this is what happened:

Warning: Illegal offset type in /Applications/MAMP/htdocs/DIG3134/battleship/battleship12.php on line 428

What's that? An 'offset' is an index, like [$x] or [$y]

What is wrong with $x or $y?

So – I whip out my trusty print_r:

Continuing the story …print "xc is "; print_r($xc);

print "ylo is "; print_r($ylo);

xc is SimpleXMLElement Object ( [0] => A )

ylo is SimpleXMLElement Object ( [0] => 1 )

What?? When I printed xc, it just looked like A

So:: the moral is, you get OBJECTS, all the way.

PHP =

-- You always gotta watch it, and be ready to jump --

Fixing the problem$y=$ylo+0; // looks weird. Add zero? Why?

print "y is ";

print_r($y);

y is 1 // problem solved.

How did this work?

PHP automatically assigns a data type to new

variables like $y, based on the types of incoming vars.

$y = $ylo + 0;

(object + number) results in a number.

Creating XML from Objects

<?php // example.php -- here's one way to create a complex string.

$xmlstr = <<XML

<?xml version='1.0' standalone='yes'?> <movie> <title>PHP: Behind the Parser</title> <characters> <character> <name>Ms. Coder</name> <actor>Onlivia Actora</actor> </character>

</characters> <plot> To save space, nothing here. </plot>

</movie>

XML;?>

Creating XML from Objects

<?phpinclude 'example.php';$movie = new SimpleXMLElement($xmlstr);

$character = $movie->characters->addChild('character');$character->addChild('name', 'Mr. Parser');$character->addChild('actor', 'John Doe');

$rating = $movie->addChild('rating', 'PG');$rating->addAttribute('type', 'mpaa');

$stringout= $movie->asXML(); // then write out text file.?>

Take-away:

1. print_r is your friend, in times of confusion.

It can print (and "explain") any PHP variable.

2. simplexml is an easy-to-use tool,

but you gotta understand objects to use it.

3. attribute-value pairs are accessed via a special

method, not simply as object variables.

Looking forward:

* Creating useful outputs(PDF, XLS)

* Reading XLS files directly

* Communicating with otherwebsites (CURL)

* Advanced topics:- recursion, JSON

DIG 3134 – Internet Software Design

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