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In engineering, some methods or components make special demands on the system. The extra design features necessary to accommodate these demands are called overhead. For instance, in electrical engineering, a particular integrated circuit might draw large current, requiring a robust power delivery circuit and a heat-dissipation mechanism.
An example from software engineering is the encoding of information and data. The date and time "2011-07-12 07:18:47" can be expressed as Unix time with the 32-bit signed integer
1310447927, consuming only 4 byte. Represented as ISO 8601 formatted UTF-8 encoded string
2011-07-12 07:18:47 the date would consume 19 byte, a size overhead of 275% over the binary integer representation. As XML this date can be written as follows with an overhead of 218 characters, while adding the semantic context that it is a CHANGEDATE with index 1.
<?xml version="1.0" encoding="UTF-8"?> <DATETIME qualifier="CHANGEDATE" index="1"> <YEAR>2011</YEAR> <MONTH>07</MONTH> <DAY>12</DAY> <HOUR>07</HOUR> <MINUTE>18</MINUTE> <SECOND>47</SECOND> </DATETIME>
The 349 byte, resulting from the UTF-8 encoded XML, correlates to a size overhead of 8625% over the original integer representation.
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