Database chapter 3

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

A table is a two-dimensional structure composed of rows and columns. It is a persistent representation of a logical relationship whose contents can be saved permanently for future use. It contains a group of related entity occurrences. A database is where these tables are stored.

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.

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

Entity integrity in databases is a condition where the rows in all of the tables can be uniquely identified using the primary key of its corresponding table. Referential integrity in databases is a condition in which every reference to an entity instance by another entity instance is valid. Every foreign key entry must either be null or a valid value in the primary key of the related table.

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

Having an entity integrity in your database is important because you can reference every row in a table and searching for a specific row will always give you right results. Failure in getting the correct data will only result in confusion and wrong decision making. Referential integrity is also important because it ensures that only a valid foreign key can be assigned to a table. You cannot add an invalid value to the related table which eliminates possible data entry errors that you might make.

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

SELECT, PROJECT, DIVIDE, PRODUCT, and JOIN

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

The table or entity set contains two hundred rows or, two hundred tuples, or entity occurrences. Each of these rows contains nine attributes.

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

• They should have the same number of attributes • The corresponding columns must share the same or compatible domains