Types of attributes in dbms: types of attributes in dbms with example. Database management system types of attributes:
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What are we going to learn?
What are attributes?
What are different types of attributes?
Examples of different types of attributes.
What are attributes?
Attributes are the properties of the entities that describe the entity.
What are entities?
Entities are the real world objects or a thing in a real world which have their independent existence.
What are attributes?
For example an EMPLOYEE entity has attributes like salary, title, name etc.
An entity has a particular value for each attributes.
Also, the attribute values of the entities become a large part of the data stored on the database.
Various types of attributes:
Several types of attributes occur in the ER model:
1. simple versus composite,
2. single valued versus multivalued,
and
3. stored versus derived
SIMPLE V/S COMPOSITE ATTRIBUTES
Composite attributes are the attributes that can further be divided into subparts which further represent more basic attributes.
Simple attributes are the attributes that cannot be divided any further. They are also called atomic attributes.
Example:
An attribute like address of an entity employee, can be divided into subpart attributes like street name, house number, city, state etc.
Whereas a simple attribute cannot be divided any further, for example gender attribute of an entity employee named “Sam” will be male. It cannot be divided any further.
Single valued v/s Multivalued attributes
Single valued attributes are the are the attributes that can have only one value at a time.
For example age attribute of a person. A person can be of only a certain age and not multiple ages.
Whereas Multivalued attributes are the attributes that can have multiple values at the same time.
For example a car can have multiple colors at the same time, like a car
Stored v/s Derived attributes
Some attribute values can directly be retrieved from the database, whereas some attribute values must be derived from other stored attribute values.
The attributes whose values are stored in the database and can directly be retrieved are called stored attributes.
Some attribute values can be derived from related attributes. These attributes are called Derived attributes.
Example
Two attributes, “date of birth” and “age” are related attributes.
When Date of birth attribute’s value is stored in the database, it can directly be retrieved and hence called stored attribute.
But even when the value of age attribute is not stored, we can derive the value of age from the related attribute, i.e. the date of birth and current date.
This is called Derived attribute, because although the value is not stored in the database, it can be derived from the related attributes.
NULL VALUE:
In some cases, some entities don’t have applicable values for some attributes.
For example, attribute apartment number, is not applicable for a house or a bungalow, because it is not part of an apartment building. Hence the value of the entity apartment number would be “NULL”.
NULL VALUE:
Another case where NULL value can be used is when we know the value exist, but we don’t know the value of that attribute for that particular entity.
For example, Height of a person, is an attribute, whose value if we don’t know, we can add it as “NULL”.
It doesn’t mean that the person has no height, or the height is not applicable, but it means that the value is not known.
COMPLEX ATTRIBUTES
Composite and multivalued attributes are can be nested arbitrarily.
To represent composite attributes, we can nest them in these parentheses() and separate each component with a comma and multivalued attributes, we can nest them in braces { }.
EXAMPLE
Suppose a person has 2 different cars and for each car he has different plate numbers, and each car has 2 different colors, each.
Then, we can nest these complex attribute in the following way.
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