FWIW, this sounds like a subset of the Query By Example stuff that
someone is working on. I don't have a URL handy since I'm on a plane,
but I think google can find it.
On Mar 3, 2007, at 8:12 AM, ranbeer makin wrote:
Here is a description of what the SKYLINE operator is:
---
Suppose you wish to purchase books and you are looking for books
with high rating and low price. However, both the criteria of
selecting books are complementary since books of higher rating are
generally more expensive. For finding such books, you'll query the
database system of the book store which will return a set of
interesting books. The word 'interesting' implies all the books
which are as good or better in both the dimensions (rating and
price) and better in at least one dimension. This set of
interesting points forms the Skyline.
Skyline operator finds points which are not dominated by other data
points. A point dominates another point if it is as good or better
in all dimensions and better in at least one dimension.
For specifying the Skyline queries, we extend SQL SELECT statement
by an optional SKYLINE OF clause as given below:
SELECT ... FROM ... WHERE...
GROUP BY ... HAVING...
SKYLINE OF [DISTINCT] d1 [MIN | MAX | DIFF], .., dm [MIN | MAX |
DIFF]
ORDER BY...
Where, d1, d2 ,…, dm denote the dimensions of the Skyline, and MIN,
MAX, DIFF specify whether the value in that dimension should be
minimized, maximized, or simply be different. When DIFF is
specified, two tuples are compared only if the value of the
attribute on which DIFF is applied is different.
When DISTINCT clause is specified and if there are two or more
tuples with the same values of skyline attributes, then only one of
them is retained in the skyline set. Otherwise, all of them are
retained.
Let's consider the above example of purchasing books with high
rating and low price.
Book Name
Rating (out of 5)
Price (Rs)
Prodigal Daughter
3
250
The city of Joy
5
400
Vanishing Acts
2
250
The Notebook
4
300
Fountain Head
5
350
Dear John
5
500
Table1. Sample of book database
Now, in order to get books with high rating and low price, you
simply can issue the following query:
SELECT *
FROM Books
SKYLINE OF rating MAX, price MIN;
The Skyline set returned will be:
Book Name
Rating (out of 5)
Price (Rs)
Prodigal Daughter
3
250
The Notebook
4
300
Fountain Head
5
350
Table2. Skyline set
From this set, you can now make your choice of books, by weighing
your personal preferences for price and rating of the books.
For more information, you can refer to:
S. Borzsonyi, D. Kossmann, and K. Stocker. The skyline operator. In
ICDE, pages 421.430, 2001
---
Thanks.
On 3/3/07, Martijn van Oosterhout <kleptog@svana.org> wrote: On
Sat, Mar 03, 2007 at 07:02:41PM +0530, ranbeer makin wrote:
> We at International Institute of Information Technology (IIIT)
Hyderabad,
> India, have extended the Postgres database
> system with the skyline operation. For this work, we were guided
by our
> Prof. Kamalakar Karlapalem
> (http://www.iiit.ac.in/~kamal/).
<snip>
> Can this piece of work contribute to PostgreSQL? If yes, then
we'll send out
> a detailed report of this project including changes
> made, issues involved/need to be solved, limitations, future
work, and the
> source code etc.
Well, that kind of depends. I have no idea what "Skyline" means so
telling us what it is would be a good start
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/
kleptog/
> From each according to his ability. To each according to his
ability to litigate.
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--
Jim Nasby [EMAIL PROTECTED]
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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