Slide 12.4: Database terminologies (cont.)

Database Terminologies (Cont.)

Databases, Tables, Rows, and Columns

Different terminologies exist:
- tables or relations,
- rows, tuples, or records, and
- columns, attributes, or fields.

A database is defined to be a set of named tables or relations:
```
   CAP = { customer, agent, product, order }
```

The heading of a table (relational schema) is the set of column names:

 Head( customer ) =
   { cid, cname, city, discnt }
 Head( customer ) =
   cid   cname   city   discnt

A database schema is the set of all relational schemes for a database.

Domains and Datatypes

SQL> CREATE TABLE customer3 (
  2    cid    CHAR(5),
  3    cname  VARCHAR(32),
  4    city   VARCHAR(32),
  5    discnt REAL );

A domain is the set where an attribute of a table takes on values from:
- The domain of the attribute city might be the set of all character strings corresponding to cities in the US.
- The domain of the discnt column might be defined as consisting of all floating-point numbers between 0.00 and 20.00.

Integrity constraints is a constraint (rule) that must remain true for a database to preserve integrity. Integrity constraints are specified at database creation time and enforced by the DBMS. For example, add an integrity constraint to the customer table to assure that the discnt column always has a value between 0.00 and 20.00 inclusive.
SQL> ALTER TABLE customer3 MODIFY 2 discnt REAL CHECK ( discnt >= 0.00 AND discnt <= 20.00 );

“Whenever you find yourself on the side of the majority,
it is time to reform (or pause and reflect).”
― Mark Twain