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In other words, XML in a relational database is a hack?
Ronald Bourret wrote:
> It's a bit hard to get used to the idea, but an "XML type" is a first
> class data type whose disk storage is optimized for XML.
>
> By analogy, think about how other data types are stored. A two byte
> integer data type is stored in two bytes where each bit is treated as a
> digit in a binary number. A ten-byte ASCII character data type is stored
> as ten bytes where each byte is treated as an integer representing an
> ASCII character. And an XML data type is stored (insert leap of faith
> here) in a structure designed to hold an XML document.
>
> What's weird about this is that we're used to thinking of relational
> data types as scalar types, whereas the XML data type has much more
> structure. However, this isn't much different than in object-relational
> databases where a column can have an object data type, although that is
> presumably mapped to a set of scalar storage locations under the covers.
>
> How the XML data type is actually stored depends on the database. For
> example, Oracle stores complete XML documents in CLOBs and indexes the
> heck out of them. SQL Server stores documents using a proprietary binary
> format in BLOBs, as well as storing them in a node table with columns
> like node ID, node name, node type, parent ID, and node value. DB2
> stores documents using a proprietary disk format that is designed for
> node-level addressability and is separate from their relational storage.
>
> Another way to think about all of this is that the XML data type is the
> exposed tip of a native XML database embedded inside a relational database.
>
> Clear as mud?
>
> -- Ron
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