Logical database design focuses on what the database should contain and how the data elements relate to each other, independent of the physical implementation. It's about defining the structure of the data and the relationships between them based on business requirements.
Key Characteristics of Logical Database Design
The characteristics of a logical database design can be summarized as follows:
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Independence from specific database and data storage structures: A logical model is not tied to any particular database management system (DBMS) or storage technology. This allows for flexibility in choosing the appropriate technology later in the database development process.
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Specification of entities and attributes to be implemented: It defines the specific entities (objects or concepts about which you want to store information) and their attributes (properties of those entities) that will be included in the database.
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Identification of business rules and relationships: It captures the business rules that govern the data and the relationships between entities and attributes.
Elements Included in a Logical Data Model
Here's a breakdown of what a typical logical data model specifies:
| Element | Description | Example |
|---|---|---|
| Entities | Real-world objects or concepts about which the database needs to store information. | Customer, Product, Order |
| Attributes | Characteristics or properties of an entity. | Customer: CustomerID, Name, Address, PhoneNumber Product: ProductID, ProductName, Price |
| Relationships | Associations between entities. These define how entities are related to each other. | A Customer places an Order. A Product is part of an Order. |
| Primary Keys | Attributes that uniquely identify each instance of an entity. | CustomerID for the Customer entity, ProductID for the Product entity. |
| Foreign Keys | Attributes in one entity that refer to the primary key of another entity. Used to establish and enforce relationships between entities. | CustomerID in the Order entity, referencing the CustomerID in the Customer entity. |
| Data Types | The type of data that each attribute will hold (e.g., text, number, date). | Name: Text, Price: Number, OrderDate: Date |
| Business Rules | Constraints and rules that govern the data and its relationships, reflecting how the business operates. These can include validation rules and integrity constraints. | An Order must have at least one Product. A Customer's age must be greater than 18. |
Example
Consider an e-commerce database. A logical data model would define entities such as Customers, Products, and Orders. It would specify the attributes for each entity, like CustomerID, Name, Address for Customer, and ProductID, ProductName, Price for Product. Furthermore, it would define the relationships between these entities, such as a Customer places an Order, and an Order contains one or more Products. Business rules, such as ensuring every Order is associated with a valid Customer, would also be defined.
