Two question about your data model

I read your working draft and I have two simple question:
1) A data model instance is defined as a forest of trees (maybe 
consisting of a single node). In Appendix B you defined two forms of 
ordering among forest nodes, highlighting  that:

"Given a single input document, a global, total order can be defined 
on 
						   nodes. In general, 
however, it may not be possible to define a global order, for example 
when a data model instance contains nodesfrom multiple input 
documents."

In Quilt definition paper (Sigmod/Pods/WebDB2000) authors, instead, 
explicitly stated that on every data model instance a total order 
relation is defined:

"Each instance of the XML Query data model (regardless of whether it 
is a complete document, a fragment of a document, or a list of 
documents) is a forest that includes a total ordering, called 
"document order," among all its nodes."

Are Quilt authors wrong or, instead, do you think to enrich XML Query 
Data Model with a mechanism for defining a total order relation among 
nodes coming from multiple input documents?

2)XML Query Data Model represents an XML document as a node-labelled 
tree, while traditional semistructured database data models exploit 
edge-labelled graphs (e.g., XML-QL). What are the main reasons behind 
your choice and what are the main advantages you think to obtain by 
using a tree representation instead of a graph representation?
-- 
Carlo Sartiani
Ph.D. Student
Computer Science Department
University of Pisa

"Here's to the crazy ones. The misfits. The rebels. The troublemakers.
The round pegs in the square holes. The ones who see things differently.
The ones that change the world!"

Received on Wednesday, 31 May 2000 08:37:56 UTC