In the world of IBM i and DB2, understanding how to structure and access data efficiently is critical for both performance and security. One key object that plays a significant role in this is the Logical File (LF).

What is a Logical File?

A Logical File is a database object that provides an alternate way to view or access data stored in a Physical File (PF). While the PF contains the actual data, the LF acts as a filter or lens—presenting the data in different formats, sequences, or subsets without duplicating the data itself.

Think of a Physical File as the full data table and Logical Files as custom views built on top of it.

Practical Applications of Logical Files

Let’s explore some real-world scenarios where Logical Files can significantly enhance data handling in DB2 on IBM i.

1. Keyed Logical Files – Accessing Data Using Different Keys

You can define Logical Files with different keys to access the same data in multiple ways:

• LF1: Access customer data by NAME

• LF2: Access the same data by EMPID

This is incredibly helpful when different programs or users need to access the same dataset using different keys for performance or functional needs.

PF:

LF1:

LF2:

2. Selected Fields – Only What You Need

Logical Files can be designed to expose only specific fields from the Physical File. This is useful when:

• You want to limit data exposure (e.g., hide sensitive fields)

• Reduce I/O by avoiding unnecessary data transfer

For example, a PF may contain 20 fields, but the LF can expose only 5 fields relevant to a specific task or user.

LF: Do not allow user to access Salary

3. Filtered Data – Retrieve Only What Matters

Logical Files can be created with select/omit criteria to filter records based on certain conditions:

• Example: Retrieve only those records where Salary > 10000

This means you don’t need to write filtering logic in your program; the LF itself returns only relevant records.

4. Restricting Data Entry – Prevent Unwanted Updates

You can use Logical Files to control write access:

• Create a read-only LF that doesn’t allow add or update operations.

• Expose only those fields or records that are safe to interact with.

• Don't allow user to add entry where Age < 18

This acts as an additional data protection layer, ensuring users or programs cannot add or alter data inappropriately.

LF:

If user try to add record where age is less than 18 then user will get error:

5. Join Logical Files – Combining Multiple Physical Files

Logical Files can also be used to join multiple Physical Files based on common fields.

• Result: A single view showing customer names along with their orders

This is particularly useful for reporting or when your application needs data from multiple sources in a unified view.

PF1 and PF2

Join LF:

Final Thoughts

Logical Files in DB2 on IBM i offer flexibility, performance optimization, and data security—all without duplicating data. Whether you're building applications or managing data access, using Logical Files effectively can greatly improve your development and operational efficiency.