In response to Michael Kay,
My definition of procedural and nonprocedural (or declarative), which I still go by, is that procedural languages require the user to specify what data is needed and how to get it, while nonprocedural languages require a user to specifying what data is needed without specifying how to get it. XPath user navigation for selecting data going down a path does require coding the data types in the order they are retrieved. This is a set of step-by-step instructions that must be exactly followed. This is a procedural process and also requires the user to have exact knowledge of the data structure.
Yes, XPath 1.0 was a navigation tool. XPath 2.0 was a predecessor of XQuery. The XQuery language is performing joins based on separate navigation requests.
Multi-leg queries (known as LCA queries) such as selecting data from one leg of a hierarchical structure based on data in another leg of the structure was used in the example at the end of the article. So there was an example demonstrating a multi-leg query.
The coordinating of the multiple legs specified in the query requires Lowest Common Ancestor (LCA ) hierarchical logic to derive only the meaningful combinations of the legs involved. This is a complex operation and is usually only practical when performed nonprocedurally and navigationlessly. This also insures the result is hierarchically correct.
As far as my opinion having no reasoned argument, my stated opinion in the article is that XML markup and XML database data need to be processed differently and I stated why in the artical. I am also planning to do a dedicated article on why XML markup and database data need to be processed differently.
Sorry for using my company’s ANSI SQL navigationless XML hierarchical Query prototype to demonstrate the example shown. If there was another navigationless XML hierarchical (LCA) query product available, I would have used it. I have been publishing my independent research on ANSI SQL's inherent hierarchical processing capability for use in SQL/XML integration for quite awhile and this research has lead up to this prototype which certainly validates this ANSI SQL hierarchical processing research and approach.
Regards,
/Mike
Michael M David Advanced Data Access Technologies, Inc. mike@adatinc.com |