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

1. The unique identifier is a numeric or alphanumeric sequence thatwithin a given scheme is associated with a single individual.UIDs allow the object to be addressed,so it can be accessed and engaged with. In case of suppliers, the supplier_id will be the unique identifier which that will help the others to identify the supplier uniquely. That is for every different supplier, the supplier_id will be different even if they have same names. This will allow anyone to distinguish between suppliers.
2. A key that has more than one attribute is known as composite key. That is, a combination of two or more columns in a table that can be used to uniquely identify each row in the table. In case of supplier, both the supplier_id and category_id(the item category that the supplier supplies) will alow any one to identify the item_price, availability and other item details. Here, unlike UID, we are suing two entities(supplier_id and category_id) that will identify terms like price, availability etc.
3. An entity of type sigle valued can only contain a single value. For example, the supplier_id is a single valued attribute, cause the supplier id will be only a single value for any supplier. An entity of type multivalued can contain either a single value or multiple values. That is, the category_id can be a multi valued attribute, cause the same supplier can hold more than one category.
4. A derived attribute is an attribute whose value can be derived from other attributes. In case of supplier, the attribute experience can be derived from employed_date, delivery_count. That is by using, employed_date and delivery_count we can derive the experience of supplier.