Postlab 3.2


1.  Databases surround us on the web and everyday life.  Now that you have a clearer idea of what database systems
do, find two examples of web sites that you believe are likely to use databases and discuss what kinds of data they 
might be storing, as in the example answer.
Amazon.com stores data about products, availability, customers, customer reviews, advertisements, etc.

e-bay.com and dell.com 

2.  Identify relationships.  Suppose you are creating a database to help a university keep track of its course
offerings.  You might have the following entities in your database, since they are distinct items in real life that
are related to each other in important ways:  course, classroom, professor, and department.  In the space below,
draw an ER diagram with a box for each of these four entities and arrows between the boxes labeled with the 
relationships they denote.  (Don't worry about what fields each of these entities should have for now.)  See the 
example ER diagram in your textbook and in Part 1 of this lab.

3.  Identify many-to-one relationships.  For each of the relationships you diagrammed above, which ones are many-to-
one?  Which ones are many-to-many?  Indicate the relationships by writing 1 or infinity at each end of the relation-
ship arrows.  If you are not sure about whether a relationship is one-to-many or many-to-many, explain why.

many to one would be the professor to the classroom
many to many would be the courses to the department

4.  Identify entities.  Suppose you are creating a database to keep track of a radio station's record collection.  
What are some of the entities your database might include?

what year, person's name, name of the album, name of different songs on the album.


5.  Query results and tables look very similar--like a set of tuples.  How are query results and tables different,
however? 
The queries do not hold data themselves but are ways of building new tables out of the existing tables.