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birth whose values may be Juma, 11101 values we can assign to an attribute and
Kivukon, and 2/3/1980, respectively. can be considered as a constraint on the
attribute’s value. Each attribute has a
(c) Relation domain. For example, for an attribute
It is a set of tuples or records with the “Grade” in a student database, its domain
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same attributes; a set of columns and rows can be a positive number between 0 Chapter Eight: Databases and Database Management Systems
as in Figure 8.8. Also, we refer to it as an and 100. Another example could be
entity that is a generalised class of people, an attribute “Regions” in the Tanzania
places, concepts, or things for which data census database in which by March 2022,
is collected, stored, and maintained. The there were 31 regions (26 from Tanzania
entity is also named Table in a database. mainland and 5 from Zanzibar); thus, the
For example, a school database may domain alphabetically is “Arusha, Dar
include Students, Classes, and Courses. es Salaam, Dodoma, Kaskazini Pemba,
Attribute Kusini Unguja , Tabora, Tanga”.

(e) Primary key
The primary key is a tuple, field, or set
of tuples or fields that uniquely identify a
Tuple record or tuple concerning a table. A table
can have only one primary key, often
denoted as PK. The primary key cannot
Relation Or Entity be null due to the dependency of other

Figure 8.8: Illustration of some relational fields concerning a table. A good example
database basic terminologies is a National Identification Number in the
National Identification Authority (NIDA)
(d) Domain database or a student registration number
The domain is a set of allowable values in a student database, as indicated in
for an attribute. It refers to a group of Figure 8.9 as “StudID.”

Figure 8.9: Example of the primary, candidate and alternate keys using a student

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Student’s Book Form Five

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