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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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