A logical table is essentially a container or an abstraction layer for one or more physical tables within a data source. It provides a way to organize and work with data at a higher level without directly interacting with the underlying physical storage.
Understanding Logical Tables
Here's a more detailed look at logical tables:
- Container for Physical Tables: Think of a logical table as a folder that holds actual database tables. It doesn't store data itself but points to physical tables.
- Row-Level Detail: The level of detail in a logical table is at the row level. When you access a logical table, you're working with individual rows of data.
- Merged Physical Tables: If a logical table contains multiple physical tables, the level of detail remains at the row level of these merged tables. This means that the data from the combined tables is presented in a unified, row-by-row view.
- Distinct and Normalized: Importantly, logical tables don't merge the underlying physical tables in the data source itself. The physical tables remain distinct and typically normalized. The logical table simply provides a unified view.
Practical Insights
- Simplified Data Access: Logical tables simplify data access by providing a single point of contact even when the data is physically spread across multiple tables.
- Data Modeling: They are often used in data modeling to represent relationships and logical groupings of data, providing a clear representation for users.
- Abstraction: Logical tables provide an abstraction layer, shielding users from the complexity of the underlying data storage mechanisms.
- Data Governance: Logical tables can facilitate data governance by allowing metadata and access control policies to be managed at the logical level, rather than directly on the physical tables.
Example
Imagine you have two physical tables: Customers and Orders. You can create a logical table named CustomerOrders that includes relevant columns from both. The underlying Customers and Orders tables remain separate, but the CustomerOrders logical table presents a merged view with customer information and their orders.
Key Takeaways
| Feature | Description |
|---|---|
| Purpose | Abstraction layer over physical tables. |
| Data Storage | Doesn't store data; references physical tables. |
| Detail Level | At the row level of the merged physical tables. |
| Normalization | Underlying physical tables remain distinct and normalized. |
| Functionality | Simplifies access to multiple tables through a unified view; facilitates data modeling. |
