INF2603 Ch4 – Relational Model Characteristics – True – False

The one-to-many (1:M) relationship is easily implemented in the relational model by putting the foreign key of the "1" side in the table of the "many" side as a primary key.

False

You can think of a table as a persistent representation of a logical relation.

True

DBMSs use indexes for many different purposes.

True

Numeric data are data on which you can perform meaningful arithmetic procedures.

True

RDBMSs enforce integrity rules automatically.

True

A null is created when you press the Enter key or the Tab key to move to the next entry without making a prior entry of any kind.

True

The DIFFERENCE operator subtracts one table from the other.

True

Tables within a database share common attributes that enable the tables to be linked together.

True

Character data can contain any character or symbol intended for mathematical manipulation.

False

In a relational model, if A determines B, C, and D, you write A = B, C, D.

False

The idea of determination is unique to the database environment.

False

A foreign key must exist in both tables that have a relationship.

False

Because the relational model uses attribute values to establish relationships among tables, many database users correctly assume that the term relation refers to such relationships.

False

The DIVIDE operation uses one single-column table (e.g., column "a") as the divisor and one two-column table (e.g., columns "a" and "b") as the dividend.

True

As rare as 1:1 relationships should be, certain conditions absolutely require their use.

True

A left outer join on tables CUSTOMER and AGENT yields all of the rows in the CUSTOMER table, including those that do not have a matching value in the AGENT table.

True

Current relational database software generally provides only a system catalog (and not a data dictionary).

True

Depending on the sophistication of the application development software, nulls can create problems when functions such as COUNT, AVERAGE, and SUM are used.

True

The order of the rows and columns is important to the DBMS.

False

In a natural join, the column on which the join was made occurs twice in the new table.

False

If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that composite key, the attribute (B) is fully functionally dependent on (A).

True

A data dictionary is sometimes described as "the database designer’s database" because it records the design decisions about tables and their structures.

True

Referential and entity integrity are two names for the same thing.

False

The practical significance of taking the logical view of a database is that it serves as a reminder of the simple file concept of data storage.

True

Tables must have the same attribute characteristics (the columns and domains must be compatible) to be used in a UNION.

True

Only a single attribute, not multiple attributes, can define functional dependence.

False

There is never a good reason to use null values in a database.

False

The SELECT operator yields a vertical subset of a table.

False

A data dictionary contains metadata—data about data.

True

Each table in a relational database must have a primary key.

True