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I am glad to announce three works related to XML:
I. Constraint Specification for XML, available at
http://www.cs.ucla.edu/~mani/webdb2003/constraints.pdf
The main things to note here are: a uniform framework by which we can
compare different constraint specification schemes. They all specify the
keys in terms of (rel, sel, field), this means for an element that
satisfies rel, the key for all elements that satisfy sel is given by the
set of path expressions in field.
Different proposals use types or path expressions for rel and sel, whereas
field is always a set of path expressions. For example, XSD uses type for
rel, and path expression for sel. Suppose XSD says something like:
Library -> (Book (sel: Author, key:name), Book, Paper)
then we can actually consider it as
Library -> (Book1, Book2, Paper) and then the key
(Book1, Author, name)
XML Schema actually uses path expression for selector. Besides this, our
main results include
(a) A new proposal where we use type for both relative and selector axes -
I argue that this seems more appropriate.
(b) Given the above assumption, we can prove that all we need is only path
expression leading to values in field. We do not need path expressions
leading to nodes..
To sum up, our key specification is (rel, sel, field) where rel and sel
are types, and field is set of path expressions. Our foreign key
specification is similar, and we also provide additional capabilities for
identifying target types for IDREF and IDREFS attributes. Our work is
again at a theoretical level, which can be translated to practice.
II. Normalization theory for XML, available at
http://www.cs.ucla.edu/~mani/webdb2003/normal.pdf
This talks about redundancies and how to understand them, and how we can
eliminate them, if we want to. Redundancies should be well-understood, as
they can cause problems with respect to updates etc.
Normalization theory is one field where relational DBs have done lot of
excellent work, and it is very good that we are able to study XML
normalization very similar to relational normalization.
III. Another work under progress is how to model real world application
scenarios in XML, this is similar to ORM etc. We study this from a DB
perspective (almost universal) - that is we want to model classes and
relationships between them.. This is work in progress and most of the
current status can be found at www.cs.ucla.edu/~mani/er03/modeling.pdf
I would be very glad to receive any comments on these works..
thanks and regards - murali.
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