Question

In a requirement gathering session, you have made notes while discussing about Suppliers, with a user from procurement team. A business analyst who is working with you looks at your notes and asks you what the terms below mean with respect to Supplier entity. Explain their meaning giving examples.

1. Unique identifier

2. Composite

3. Single vs Multi-valued

4. Derived

Answer 1

Unique identifier: It is an attribute of an entity which identifies it uniquely. Basically, by identifying any entity with its name may cause some inconsistency due to presence of of multiple same names of two different entities. So it is an in absolute necessity for us to give a unique identifier such as serial number or ID to the entity and this serial number is known as unique identifier.

Composite attribute: Some attributes such as date of birth or date of joining have multiple different data combined together to form the attribute. For example, date of birth consists of three different sub attributes which are day, month and year. All three sub attitudes are composed together to form date of birth and hence date of birth is a composite attribute of day, month and year.

Single and multi valued attribute: Many attributes of entities have single value and many are multiple-valued too. For example, name is a single valued attribute since name can have only one value; a person cannot have more than one name. Mobile number can have multiple value where a person can have more than one service provider phone number. So, the phone number is multiple valued attribute.

Derived attribute: Some attributes of an entity are not directly entered into the database but they are calculated with the help of other attributes present in the database. For example, age can be calculated with the help of date of birth attribute by subtracting the value of date of birth from the value of current date. This will find the age for an entity.