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Explain different type of data attributes.

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Different types of data attributes are:
a.      Key & Non-Key Attribute: Key attributes are those attributes which uniquely identifies an entity. Non-Key are all those attributes which are not a key. For example: in entity student, student_roll_number can be primary key as it uniquely identify the entity student, other all attributes like first_name, middle_name, last_name, address, date_of_birth etc. are non-key attributes.

b.      Single & Composite Attribute: Composite attributes are the attributes having many parts to them whereas Single attributes are those which does not. Composite attributes can be sub-divided into other single attributes, which will still have its meaning. Single attributes are simple an attribute which cannot be sub divided. For example: consider an entity student having an attribute: name, which can be divided: first_name, middle_name and last_name. Here, the attribute, name can be considered as composite attribute and first_name, middle_name and last_name.

c.       Single-valued & Multi-valued Attributes: Single-valued attributes can only have one value while multi-valued attributes usually can store multiple data in them. For example: in entity student, attribute address can be considered as multi-valued, as it can hold multiple values like street address, city etc. and student’s last_name can be considered as single valued attribute as a student have only one last_name.

Derived attributes: Derived attributes are those attributes whose value can be calculated from other attributes. For Example: in entity student, attribute age can be calculated form attribute date_of_birth.
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