Slide 8.22: SQL approaches

SQL Approaches

Learning how to use a new language is an arduous task for users. A new system which uses a familiar language is usually adopted smoothly by the users. This approach views the Web as a huge database, where each record matches a web page, and designs an SQL-like language to support effective and flexible searches.

Syntax (SQL + Regular Expressions)

 query := SELECT select_cause
           FROM from_clause
           [ WHERE condition_clause ];
select_clause := arguments
from_clause := path

Find documents about Toronto that reside in servers in Canada.

 SELECT d.url, d.title
   FROM Document d SUCH THAT d MENTIONS "Toronto"
   WHERE d.url CONTAINS ".ca$";

Find documents about “excursions” near WWW6 homepage.

 SELECT d.url, d.title
   FROM Document d SUCH THAT d MENTIONS
     "www6conf.slac.stanford.edu" (→|→→|→→→) d
   WHERE d.text CONTAINS "excursions";

Path Regular Expression
→	Local link: same server
⇒	Global link: different server
→\|⇒	Path of length one, either local or global
→*	Local path of any length

Find educational pages containing the keyword “database.”
SELECT url FROM http://*.edu/* WHERE keyword LIKE 'database';
where the symbol ‘*’ is a wild card matching any string.