I remember wondering what the big deal was with the Exception type. I guess it was annoying not being able to return an error from, say, constructors:
"The use of exceptions adds to a consistent framework design and allows error reporting from members, such as constructors, that cannot have a return type." - http://msdn.microsoft.com/en-us/library/ms229014
Tuesday, July 10, 2012
Friday, July 6, 2012
Nodes aren't just elements...
Caught myself thinking that. So to set my mind right:
According to the DOM, everything in an XML document is a node.
The DOM says:
- The entire document is a document node
- Every XML element is an element node
- The text in the XML elements are text nodes
- Every attribute is an attribute node
- Comments are comment nodes
Text is Always Stored in Text Nodes
A common error in DOM processing is to expect an element node to contain text.
However, the text of an element node is stored in a text node.
In this example: <year>2005</year>, the element node <year>, holds a text node with the value "2005".
"2005" is not the value of the <year> element!
This is exacerbated by JavaScript referring to nodeValue ....
This is exacerbated by JavaScript referring to nodeValue ....
XML Elements vs. Attributes
XML Elements vs. Attributes
Take a look at these examples:
<person sex="female">
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>
<person>
<sex>female</sex>
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>
<sex>female</sex>
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>
In the first example sex is an attribute. In the last, sex is an element. Both examples provide the same information.
There are no rules about when to use attributes or when to use elements.
However, YOU SHOULD AVOID USING ATTRIBUTES WHEN POSSIBLE. USE ELEMENTS INSTEAD. (except for true MetaData)
The following three XML documents contain exactly the same information:
A date attribute is used in the first example:
<note date="10/01/2008">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<note>
<date>10/01/2008</date>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<date>10/01/2008</date>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<note>
<date>
<day>10</day>
<month>01</month>
<year>2008</year>
</date>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<date>
<day>10</day>
<month>01</month>
<year>2008</year>
</date>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
Avoid XML Attributes?
Some of the problems with using attributes are:- attributes cannot contain multiple values (elements can)
- attributes cannot contain tree structures (elements can)
- attributes are not easily expandable (for future changes)
Don't end up like this:
<note day="10" month="01" year="2008"
to="Tove" from="Jani" heading="Reminder"
body="Don't forget me this weekend!">
</note>
to="Tove" from="Jani" heading="Reminder"
body="Don't forget me this weekend!">
</note>
XML Attributes for Metadata
Sometimes ID references are assigned to elements. These IDs can be used to identify XML elements in much the same way as the id attribute in HTML. This example demonstrates this:
<messages>
<note id="501">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<note id="502">
<to>Jani</to>
<from>Tove</from>
<heading>Re: Reminder</heading>
<body>I will not</body>
</note>
</messages>
<note id="501">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
<note id="502">
<to>Jani</to>
<from>Tove</from>
<heading>Re: Reminder</heading>
<body>I will not</body>
</note>
</messages>
So, metadata (data about data) should be stored as attributes, and the data itself should be stored as elements.
excerpted from http://www.w3schools.com/xml/xml_attributes.asp
new line
In Windows applications, a new line is normally stored as a pair of characters: carriage return (CR) and line feed (LF). In Unix applications, a new line is normally stored as an LF character. Macintosh applications also use an LF to store a new line.
XML stores a new line as LF.
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