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What is the XML metadata format?


ECS Metadata is now generated in Extensible Markup Language (XML) format, with file
extension .xml, instead of the old ODL format, with file extension .met .
The main reason an XML file is useful in ECS is because it is a commonly accepted portable data
format, which makes it easier for interested third parties to write software to manipulate it.
XML is not a data format description itself, but rather a framework and syntax for defining one.

In addition, XML data are able to be displayed in user-defined ways in common web browsers.
For example, the particular metadata attributes displayed in a browser can be easily changed by
changing a stylesheet, which is a text file that describes how the metadata is formatted for the
browser.

At the nuts and bolts level, XML and ODL are simply different file formats.
For example, part of an ODL .met file might look like:

GROUP = RANGEDATETIME
OBJECT = RANGEENDINGTIME
NUM_VAL = 1
VALUE = "01:00:00.000000"
END_OBJECT = RANGEENDINGTIME

OBJECT = RANGEENDINGDATE
NUM_VAL = 1
VALUE = "2000-06-08 00:00:00.0"
END_OBJECT = RANGEENDINGDATE
END_GROUP = RANGEDATETIME

The equivalent XML representation is:

<RangeDateTime>
<RangeEndingTime>01:00:00.000000</RangeEndingTime>
<RangeEndingDate>2000-06-08 00:00:00.0</RangeEndingDate>
</RangeDateTime>

The data model to which a given XML file must adhere is called a Data Type Definition (DTD).
The DTD specifies the allowed attributes and tags. For ECS, the metadata DTD implements the
ECS Data Model. A variety of parsers and validators exist for ensuring XML documents are both
syntactically correct, and adhere to their DTDs. (An XML Schema is an alternate way to define a
data model in XML.)






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