A sample movie database spans semistructured data from a total of six sites. The Internet Movie Database site contains a wealth of movie data; Videotastic is a monthly, on-line movie industry magazine, portions of which are available only by subscription; the Haus du Flicks site charges a fee in e-cash for access to each of its many film clips, the fee being collected by an e-cash broker when a clip is accessed; Joe Doe is a Yankee On-line User site devoted to science fiction movies; the site Horsing Around Movies has data about R- and NC-18 rated films, portions of which are restricted to web surfers over the age of 18; and the Internet Archives site offers movie data collected by a robot that periodically traverses part of the web.
Figure 2 shows a portion of the movie database. Edges are directed arrows, values are given in italics, and objects are depicted as ovals. Most of the semistructure is not shown--many other edges and nodes exist in the complete movie database.
The database models the following pertinent facts. Information about a new movie, Star Wars IV, was added to the database on 31/Jul/1998. A review of this movie appeared in the June issue of Videotastic, which was made available on 25/May/1988. The review is only available to paid subscribers. Joe Doe also has a review of Star Wars IV, but since he is a Yankee On-line User, it is deemed to be of low quality. Haus du Flicks charges $2 dollars for a Star Wars IV film clip, but under a deal with Videotastic, paid subscribers can get the clip for free in one of the magazine's reviews. Bruce Willis stars in Star Wars IV. His misspelled name was corrected on 2/Apr/1997. Finally, Horsing Around Movies has data about the NC-18 rated movie, Color of Night, which also stars Bruce Willis. Only surfers with an appropriate security clearance are permitted to view this movie.
We will use this sample database for illustration throughout the paper.