People who develop the application programs need to know the logical schema of the database completely.

This statement is partially correct. Application developers need to understand the logical schema of a database to a certain extent. The logical schema of a database refers to its structure and organization, including how data is stored, organized, and accessed. This knowledge is crucial for developers to design and implement effective applications that interact with the database.

However, they do not necessarily need to know the logical schema "completely". The level of understanding required can depend on the complexity of the application and the database, as well as the specific tasks the developer is responsible for. For example, a developer working on a simple application that only interacts with a small part of the database might not need to understand the entire logical schema.

Moreover, in many development environments, there are abstraction layers (like ORM - Object-Relational Mapping) that allow developers to interact with databases in a more intuitive way, without needing a deep understanding of the underlying schema.

So, while a good understanding of the logical schema can certainly be beneficial for application developers, it is not always a strict requirement for them to know it completely.