Data Exchange with XML, WDDX and PHP - Polly Wants A Cracker

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Since WDDX data follows the basic rules of XML markup, it can easily be validated against a DTD. And if you look at the DTD, you'll quickly see that all WDDX "packets" are constructed in a standard format.

The root, or document, element for WDDX data is always the <wddxPacket> element, which marks the beginning and end of a WDDX block.

<wddxPacket version='1.0'>

This is immediately followed by a header containing comments,

<header>
<comment>Who da man?</comment></header>

and a data area containing the XML representation of the data structure.

<data>
...</data></wddxPacket>

This data area can contain any of WDDX's basic datatypes, which are described in detail in the WDDX DTD - here's the short version, with examples:

Boolean values, represented by the element <boolean> - for example

<wddxPacket version='1.0'>
<header/><data><struct><var name='validUser'><boolean value='true'/></var></struct></data></wddxPacket>

Numbers, represented by the element <number> - for example

<wddxPacket version='1.0'>
<header/><data><struct><var name='page'><number>76</number></var></struct></data></wddxPacket>

String values, represented by the element <string> - for example

<wddxPacket version='1.0'>
<header/><data><struct><var name='phrase'><string>Polly wants a cracker</string></var></struct></data></wddxPacket>

Arrays and hashes (or associative arrays), represented by the elements <array> and <struct> respectively - for example

<wddxPacket version='1.0'>
<header/><data><struct><var name='desserts'><array length='5'><string>apple pie</string><string>angel food cake</string><string>chocolate fudge</string><string>strawberries and cream</string><string>tiramisu</string></array></var></struct></data></wddxPacket>

Tabular data, represented by the element <recordset> - for example

<wddxPacket version='1.0'>
<header/><data><recordset rowCount="2" fieldNames="symbol, price"><field name="symbol"><string>HDST</string><string>BDGF</string></field><field name="price"><number>56.78</number><number>373.03</number></field></recordset></data></wddxPacket>

Timestamps, represented by the element <dateTime> - for example

<wddxPacket version='1.0'>
<header/><data><struct><var name='today'><dateTime>2001-08-08T16:48:23</dateTime></var></struct></data></wddxPacket>

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