Business logic refers to the custom rules and algorithms that process the exchange of information between a user’s screen and a database. It contains the operational policies and procedures that constrain how a business operates. Business logic acts as the brain of an application, making decisions and determining how data is created, stored, and changed.
The Core Components of Business Logic
Business logic is composed of two elements: business rules and workflows. Business rules are the specific criteria and constraints that govern business operations. These are often expressed as straightforward conditions, such as a rule stating that a customer’s password must contain at least eight characters or that a user cannot withdraw more money than their available balance.
Workflows are the sequence of steps or ordered tasks that put business rules into motion. A workflow dictates the procedural flow of data, executing tasks according to established rules. For example, the user login process is a workflow: it checks if the username exists, validates the password, and then grants or denies access. This sequence of actions is guided by the business rules for valid credentials.
Examples of Business Logic in Action
E-commerce Website
On an e-commerce platform, business logic manages numerous functions. When a customer adds an item to their cart, logic is applied to ensure inventory levels are adequate. During checkout, the system calculates shipping costs based on rules like package weight, destination, and shipping speed. If a customer enters a discount code, the business logic validates the code, checks its eligibility, and adjusts the final price.
Banking Application
In a banking application, business logic is responsible for complex calculations and transaction enforcement. It dictates how monthly interest is calculated on a savings account, applying the correct rate to the balance. When a customer applies for a loan, the application’s logic evaluates their eligibility by processing data against a set of rules, such as checking their credit score, verifying income, and comparing their debt-to-income ratio to the bank’s lending standards.
Social Media Platform
The feed a user sees on a social media platform is a direct result of business logic. An algorithm, which is a complex set of business rules and workflows, determines which posts are most relevant to the user and in what order they should appear. Another example is the rule that prevents a user from creating a username that is already in use. The logic queries the database to ensure the chosen name is unique before allowing account creation.
Ride-Sharing App
Ride-sharing apps use business logic to manage their dynamic operating environments. A prominent example is surge pricing, where fares are automatically adjusted based on real-time data. The logic analyzes the ratio of available drivers to rider requests in a specific area. When demand outpaces supply, the business rules dictate that the price should increase to incentivize more drivers to enter that area.
Where Business Logic Lives in an Application
In modern software design, applications are structured using a three-tier architecture, which organizes the program into distinct layers: the presentation tier, the application tier, and the data tier. Business logic resides in the middle layer, the application tier, often called the business logic layer (BLL). This layer acts as an intermediary, managing communication between the user interface and the database.
The presentation tier is the user interface (UI) people interact with, while the data tier is the database responsible for storing information. The BLL sits between them, processing requests from the presentation layer, applying its rules, and interacting with the data layer. This structure ensures the core operations of the business are not directly tied to how information is displayed or stored.
Why Separating Business Logic is Important
Isolating business logic into its own layer provides practical advantages for developing and managing software. A primary benefit is improved maintainability. When business rules change, developers can modify the logic in the business layer without altering the user interface or database structure. This separation makes updates faster and reduces the risk of introducing bugs into other parts of the application.
This modularity also promotes reusability, as the same business logic can serve multiple user interfaces. For instance, a company’s website and mobile app can both use the same business logic layer to process orders or manage user accounts. This prevents code duplication and ensures rules are applied consistently across all platforms.
This separation also supports scalability and simplifies testing. Different layers of the application can be scaled independently, so the business logic layer can be enhanced without impacting the others. Testers can also focus on verifying the business logic on its own, ensuring calculations and workflows are correct without interference from UI elements.