Datasheet

Chapter 1 ✦ An Eagle’s Eye View of XML

Self-describing data

Much computer data from the last 40 years is lost, not because of natural disaster or

decaying backup media (though those are problems too, ones XML doesn’t solve),

but simply because no one bothered to document how the data formats. A Lotus 1-2-3

file on a 15-year-old 5.25-inch floppy disk might be irretrievable in most corporations

today without a huge investment of time and resources. Data in a less-known binary

format such as Lotus Jazz may be gone forever.

XML is, at a low level, an incredibly simple data format. It can be written in 100 per-

cent pure ASCII or Unicode text, as well as in a few other well-defined formats. Text

is reasonably resistant to corruption. The removal of bytes or even large sequences

of bytes does not noticeably corrupt the remaining text. This starkly contrasts with

many other formats, such as compressed data or serialized Java objects, in which

the corruption or loss of even a single byte can render the rest of the file unreadable.

At a higher level, XML is self-describing. Suppose you’re an information archaeologist

in the twenty-third century and you encounter this chunk of XML code on an old

floppy disk that has survived the ravages of time:

<NAME>

<GIVEN>Judson</GIVEN>

<SURNAME> McDaniel</SURNAME>

</NAME>

<BIRTH>

<DEATH>

</PERSON>

Even if you’re not familiar with XML, assuming you speak a reasonable facsimile of

twentieth-century English, you’ve got a pretty good idea that this fragment describes

a man named Judson McDaniel, who was born on February 21, 1834 and died on

December 9, 1905. In fact, even with gaps in or corruption of the data, you could

probably still extract most of this information. The same could not be said for a

proprietary, binary spreadsheet or word-processor format.

Furthermore, XML is very well documented. The World Wide Web Consortium

(W3C)’s XML specification and numerous books tell you exactly how to read XML

data. There are no secrets waiting to trip the unwary.

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