In low-level design, entities represent the key objects or concepts within a system. These entities can include user accounts, products, orders, transactions, and more. Defining entities accurately is crucial for building a well-designed system.
To define entities and their relationships, you can follow these steps:
Identify the Entities: Begin by identifying the main entities in your system. Consider the different types of data that need to be stored and manipulated in your application. For example, in a payment app, you may have entities like 'User', 'Payment', 'Transaction', 'Product', and 'Cart'.
Establish Relationships: Once you have identified the entities, determine the relationships between them. Relationships can be one-to-one, one-to-many, or many-to-many. For example, a 'User' can have multiple 'Payments' or 'Transactions', and a 'Cart' can contain multiple 'Products'. Use appropriate notations like associations, aggregations, or compositions to represent these relationships in your design.
Define Attributes: For each entity, define the attributes or properties that it possesses. Attributes represent the data associated with an entity. For example, a 'User' entity may have attributes like 'name', 'email', and 'password'. Similarly, a 'Product' entity may have attributes like 'name', 'price', and 'quantity'.
Consider Cardinality and Multiplicity: Cardinality and multiplicity define the number of instances that can be associated with a relationship. For example, a 'User' can have one-to-many 'Transactions', meaning a single user can have multiple transactions, but each transaction is associated with only one user.
Once you have gone through these steps, you will have a clear understanding of the entities within your system and their relationships. This will serve as a foundation for further steps in the low-level design process, such as creating a class diagram and designing a database schema.
Let's put these concepts into practice with an example:
Consider a payment app where users can make payments and track their transactions. In this app, the main entities could be:
- User
- Payment
- Transaction
- Product
The relationships between these entities would be:
- A User can have multiple Payments and Transactions
- A Payment belongs to one User
- A Transaction belongs to one User
- A Transaction is linked to one Payment
- A Payment can have multiple Products
- A Product is associated with multiple Payments
The attributes for each entity would include:
- User: name, email, password, etc.
- Payment: amount, date, status, etc.
- Transaction: type, description, date, etc.
- Product: name, price, quantity, etc.
Keep in mind that these are just examples, and in real-world scenarios, the entities, relationships, and attributes may vary based on the specific requirements of your application.
Now that we have defined the entities and relationships for our payment app, we can proceed to the next steps in the low-level design process.