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C # tutorial
An XML document contains XML Elements
An XML element is everything from (including) the element's start tag to (including) the element's end tag.
<price>29.99</price>
An element can contain:
<bookstore>
<book category="children">
<title>Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="web">
<title>Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>
In the example above:
<title>, <author>, <year>, and <price> have text content because they contain text (like 29.99).
<bookstore> and <book> have element contents, because they contain elements.
<book> has an attribute (category="children").
An element with no content is said to be empty.
In XML, you can indicate an empty element like this:
<element></element>
You can also use a so called self-closing tag:
<element />
The two forms produce identical results in XML software (Readers, Parsers, Browsers).
Empty elements can have attributes.
XML elements must follow these naming rules:
Any name can be used, no words are reserved (except xml).
Create descriptive names, like this: <person>, <firstname>, <lastname>.
Create short and simple names, like this: <book_title> not like this: <the_title_of_the_book>.
Avoid "-". If you name something "first-name", some software may think you want to subtract "name" from "first".
Avoid ".". If you name something "first.name", some software may think that "name" is a property of the object "first".
Avoid ":". Colons are reserved for namespaces (more later).
Non-English letters like éòá are perfectly legal in XML, but watch out for problems if your software doesn't support them!
Some commonly used naming conventions for XML elements:
Style | Example | Description |
---|---|---|
Lower case | <firstname> | All letters lower case |
Upper case | <FIRSTNAME> | All letters upper case |
Snake case | <first_name> | Underscore separates words (commonly used in SQL databases) |
Pascal case | <FirstName> | Uppercase first letter in each word (commonly used by C programmers) |
Camel case | <firstName> | Uppercase first letter in each word except the first (commonly used in JavaScript) |
XML documents often have a corresponding database. A common practice is to use the naming rules of the database for the XML elements.
XML elements can be extended to carry more information.
Look at the following XML example:
<note>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this weekend!</body>
</note>
Let's imagine that we created an application that extracted the <to>, <from>, and <body> elements from the XML document to produce this output:
To: Tove
From: Jani
Don't forget me this weekend!
Imagine that the author of the XML document added some extra information to it:
<note>
<date>2008-01-10</date>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
Should the application break or crash?
No. The application should still be able to find the <to>, <from>, and <body> elements in the XML document and produce the same output.
This is one of the beauties of XML. It can be extended without breaking applications.