What is it impossible to formulate complex queries?

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Hello,

I am working on a data extraction project.
I think I don’t understand this because I am not a database developer :)
I got the paragraph below from a paper on data extraction.
My question is: why is it not possible to have restricted (complex) queries?
Why is it impossible to formulate such queries?
It does not look trivial to me :(
The way I see queries is: You can formulate any query, no matter how complex it is.

Imagine you would like to monitor interesting eBay
offers (www.ebay.com) of notebooks, where an interesting
offer is, for example, defined by an auction item
which contains the word \notebook", has current value
between gbp 1500 and 3000 and which has received at
least three bids so far. The eBay site does not offer the
possibility to formulate such complex queries. Similar
sites do not even give restricted query possibilities and
leave you with a large number of result records organised
in a huge table split over many web pages. You
have to wade through all these records manually, because
of no possibility to further restrict the result.

Thanks in advance :)

Posted 7-Apr-11 22:39pm

The_Real_Chubaka

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OriginalGriff · Accepted Answer · 2011-04-07T23:03:00

Solution 1

It isn't impossible to formulate such queries, but it is very difficult to design a user interface that allows non-technical people to construct them, without scaring off the ~~idiots that will by any old tat on eBay~~ average eBay user.

Think about it: Google lets you do some of this, with Advanced searches, and "+" and "-" prefixes, "site:" definitions, "Define:" etc., but it is not advertised because it is hard for "normal users" to understand.

Posted 7-Apr-11 23:03pm

OriginalGriff

Comments

The_Real_Chubaka 8-Apr-11 5:15am

Thanks. I am actually working on a project where i have to use machine learning theory to automatically construct wrapper to extract data from thousands of web pages and put them together on common database.

This makes more sense now :)

Sergey Alexandrovich Kryukov 9-Apr-11 0:07am

Nice style with using scratch! My 5 (I mean because it's also correct).
--SA