Datasheet

The markup in XML documents consists of data enclosed in elements, where that data may consist of

nested (child) elements. Every XML document contains a single root (or document) element, and ele-

ments nested within the root element make up a hierarchy of data. Apart from the root element, XML

documents may contain a single XML declaration, and zero or more processor directives. Each element,

including the root element, has either a start tag and an end tag, or a single empty element tag. Start tags

and empty element tags can include attributes that consist of name/value pairs.

Here’s an example of an XML document:

<?xml version=”1.0” encoding=”utf-8” ?>

<name>Cheese and Tomato</name>

</foodStuff>

<name>Four Seasons</name>

</foodStuff>

</foodStuffs>

The XML declaration on the first line of the document identifies the version of XML to which the docu-

ment conforms and how it is encoded (that is, the character set used). The root element of the document

<foodStuffs>, which contains two <foodStuff> elements. Each <foodStuff> element has an

attribute called

category, and child elements called <name>, <size>, and <rating>, each of which

contains text data. Each of these elements consists of a start tag (for example,

<size>) and an end tag

that includes a preceding front slash (<

/size>). The second <foodStuff> element also contains an

empty element,

<isNasty>, which includes a trailing front slash to indicate that the element is empty.

One way of looking at this document is as an array of

foodStuff objects, each of which has properties

that are represented as attributes or child elements.

There are a few more rules concerning XML documents. For a start, they are case-sensitive.

<foodStuff> and <Foodstuff>, for example, are interpreted as two completely different elements.

Also, every start tag must have a matching end tag, and elements can’t overlap, that is to say that the fol-

lowing is illegal:

Here’s an example in which <element2> is correctly nested inside <element1>:

And in this example, neither element is nested in the other:

Database Fundamentals

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