[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML vs relational database
Sylvain Lousieu wrote: >For instance, one can ask for a structural property of the tree, in >XPath, say the name of an element, by (1) referring to this element >by its position and (2) using local-name() : >local-name(./children[1]). In a relational algebra model, there is >no order of the field, if I understand correctly. I see no other way >of adressing a field than by its name. Jim Melton wrote: >>the call-level interface (CLI, of which ODBC is >>an implementation) defined in 9075-3:2003 (soon to be 2008) defines >>an API to get the same information without having to do all those >>annoying SELECTs ;^) >>It is true that in the relational model of data, attributes (columns) >>have no order with a relation (table). However, in the SQL model, >>columns are, in fact, ordered. In spite of that, the SQL standard >>strongly(!) discourages code that depends on the sequence of columns >>within a table. SQL/CLI and JDBC provide metadata about a database and query result sets. For operating with a column of a result set (rowset), a JDBC program can, for example, access it by name or ordinal position. In some early drivers, accessing a column by index was less prone to errors than accessing it by name. But a core concept of SQL database technology has been to free applications from navigational logic and details of the physical data model. The idea is to provide operations at a logical level, using a database engine that optimizes queries and produces a plan for physical access to the data. If physical data independence and operating at a logical level had been prime directives during the development of the XML specs, we might be talking about nested sets (which preserve order) as the XML document model.
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