Database Systems: Design, Implementation, and Management, 11th Edition. Chapter 3 Review Questions

1. What is the difference between a database and a table?

A table is a logical structure that represents an entity set. It is only one of the components of a database. The database is a structure that houses one or more tables and metadata. The metadata includes the data characteristics and the relationships between the entity sets.

7. A database user manually notes that "The file contains two hundred records, each record containing nine fields." Use appropriate relational database terminology to "translate" that statement.

An entity set contains two hundred tuples with each record consisting of nine attributes.

6. Explain why the data dictionary is sometimes called "the database designer's database."

Because it contains metadata relating to the datatypes used and sizes as well has the relations in the database.

2. What does it mean to say that a database displays both entity integrity and referential integrity?

Entity integrity describes a condition in which all tuples with a table are uniquely identified by their primary key. The unique value requirement prohibits a null primary key value, because nulls are not unique. Referential integrity describes a condition i which a foreign key value value has a match i the corresponding table or in which the foreign key value is null. The null foreign key value makes it possible not to have a corresponding, but the matching requirement on values that are not null make it impossible to have an invalid value.

3. Why are entity integrity and referential integrity important in a database?

Entity integrity is important because it means that a proper search for an existing tuple will always be successful and the failure to find a match on a row search will always mean that the row for which the search is conducted does not exist in that table. Referential integrity is important because its existence ensure that it will be impossible to assign a non existing foreign key value to a table. For example, the referential integrity enforcement in a SALESREP is assigned to CUSTOMER relationship means that it will be possible for a customer to not have a sales rep assigned to him or her but it will be impossible to assign non existing sales rep to a customer.

5. Which relational algebra operators can be applied to a pair of tables that are not union-compatible?

SELECT, PROJECT, DIVIDE, PRODUCT, and JOIN

4. What are the requirements that two relations must satisfy to be considered union-compatible?

Using the proper relational terminology, the statement may be translated to " the table or entity set contains two hundred rows/tuples.