Oracle
Business key, Natural key and Candidate Key
In relational database management systems (RDBMS), keys are essential for uniquely identifying records in a table. They play a crucial role in database design and ensuring data integrity. Here’s a beginner-friendly overview of three important types of keys: Business Key, Natural Key, and Candidate Key.
Business Key
- Definition: A Business Key is a unique identifier used in the real world to identify an entity within a business context. It is often used outside the database system.
- Example: A Customer ID or ISBN for a book.
- Usage: It’s not always the primary key in the database but is often used as a reference.
-- Example: Creating a table with a business key CREATE TABLE customers ( customer_id VARCHAR2(20) PRIMARY KEY, -- Business Key name VARCHAR2(50), email VARCHAR2(100) );Natural Key
- Definition: A Natural Key is a key that has a logical relationship to the data it identifies and is derived from the data itself.
- Example: Social Security Number (SSN) for a person, or an ISBN for a book.
- Usage: It is a type of business key that is used within the database to uniquely identify records.
-- Example: Creating a table with a natural key CREATE TABLE books ( isbn VARCHAR2(13) PRIMARY KEY, -- Natural Key title VARCHAR2(100), author_id NUMBER );Candidate Key
- Definition: A Candidate Key is a field, or combination of fields, that can uniquely identify each record in a table. There can be multiple candidate keys in a table, and one is chosen as the Primary Key.
- Example: For a table of library books, both ISBN and a combination of book title and author could be candidate keys.
- Usage: Candidate keys are evaluated to choose the primary key of the table.
-- Example: Defining candidate keys in a table CREATE TABLE rentals ( rental_id NUMBER PRIMARY KEY, -- Primary Key (a candidate key) book_id NUMBER, -- Another candidate key member_id NUMBER, rental_date DATE ); -- Alternative candidate key example ALTER TABLE rentals ADD CONSTRAINT unique_rental UNIQUE (book_id, member_id, rental_date); -- Composite Candidate Key
Each type of key serves a unique purpose and is used to maintain the integrity and organization of the data within a relational database.
Business Key
Definition
A Business Key (also known as a Domain Key) is a data attribute or set of attributes that have a meaningful value in the business domain and are used to identify or reference an entity uniquely within a business context. Business keys are chosen based on business logic and are often visible and understandable by end-users.
Characteristics
- Business Relevance:Directly related to the business domain, making them intuitively understandable to business users.
- Uniqueness:Ideally, a business key should uniquely identify a record without ambiguity.
- Stability:Should be relatively stable over time, although not as strictly invariant as surrogate keys.
Use Cases
Business keys are commonly used in scenarios where data needs to be integrated or matched across different systems or databases, relying on business concepts. For example, a customer's social security number (SSN) or a product's SKU number can serve as a business key.
Natural Key
Definition
A Natural Key (also known as a Natural Business Key) is a type of business key that naturally occurs in the real world and is used within databases to uniquely identify a piece of data. It is derived from the existing attributes of the data that are inherent to the entity being represented.
Characteristics
- Inherent:Derived from the data's natural attributes without artificial generation.
- Uniqueness:Uniquely identifies data entities in a natural manner.
- Understandability:Often immediately recognizable and meaningful to users.
Use Cases
Natural keys are used when the uniqueness of a record is defined by real-world attributes. Examples include email addresses for user accounts or vehicle identification numbers (VINs) for cars.
Candidate Key
Definition
Candidate Keys are a set of attributes (or a single attribute) in a table that can qualify as a unique key for identifying rows in the table. A table can have multiple candidate keys, each capable of uniquely identifying a row.
Characteristics
- Uniqueness:Every candidate key must uniquely identify each row in a database table.
- Non-Redundancy:No two rows can have the same value for candidate keys.
- Minimality:A candidate key must be minimal, meaning that removing any attribute from it would result in losing its property of uniqueness.
Use Cases
Candidate keys are considered when designing databases to ensure data integrity and uniqueness. From the set of candidate keys, one is chosen as the primary key for the table, while others can serve as alternate keys or be used to enforce uniqueness through unique constraints.
Key Differences and Relations
Business vs. Natural Key:While both are meaningful within the business domain, natural keys are a subset of business keys that are inherently found in the data. Business keys might not always be natural; they could be imposed by business processes.
Candidate Keys vs. Natural/Business Keys:Candidate keys are a broader concept that includes any potential key that can uniquely identify table rows, including both natural/business keys and surrogate keys. The primary key is a special case of a candidate key that is chosen to serve as the main unique identifier for table rows.
Conclusion
The selection of keys in database design is a critical decision that affects data integrity, performance, and usability. Business keys and natural keys are closely tied to the business domain, offering meaningful ways to identify records. Candidate keys offer a more technical perspective, highlighting all possible unique identifiers from which the primary key is chosen. Understanding these concepts is essential for effective database schema design, ensuring that data remains accurate, consistent, and accessible.
SAMPLE DATA FOR BUSINESS KEY, NATURAL KEY AND CNDIDATE KEY
Department Table
Business Key:
department:This could be a Business Key as it represents a meaningful value in the business domain and is used to uniquely identify a department within the business context.
Natural Key:
There isn't a clear Natural Key in the Department Table as presented. However, if the department names are unique and not subject to change, thendepartmentcould also be considered a Natural Key.
Candidate Keys:
- department_id:This is a strong candidate key because it is unique for each department.
- department:This could also be a candidate key if the department names are guaranteed to be unique.
Employee Table
Business Key:
- employee_number:This might be a Business Key since it appears to be a unique identifier used within the business to identify employees.
- email:Could also serve as a Business Key because emails are unique identifiers in a business context.
Natural Key:
email:Assuming that each employee has a unique email address, this could be a Natural Key because it is a real-world unique identifier that naturally occurs.
Candidate Keys:
- employee_id:Clearly a candidate key as it is a unique attribute for each employee.
- employee_number:If this is unique across the organization, it also qualifies as a candidate key.
- email:If unique, this is another candidate key.
Note that for thedepartment_idin the Employee Table, it's a foreign key that relates to thedepartment_idin the Department Table, establishing a relationship between the two tables.
Key Distinctions and Relations
- Business Keysare defined by business need and may not always be the primary key in database design.
- Natural Keysare keys that naturally and obviously identify an entity, such as an email or social security number.
- Candidate Keysare any keys which could serve as the primary key. In practice, one of them is chosen to be the primary key based on factors like stability and simplicity, and the others may be used for alternate indices or constraints.
Comments Not Found