In a database system, the capacity to change the conceptual schema without having to change external schemas or application programs is called what type of data independence?

Introduction / Context:
Data independence is a key goal of database management systems and is one of the reasons they are preferred over file based systems. The idea is to separate different levels of the database so that changes at one level do not force changes at others. Understanding the difference between physical and logical data independence is essential for appreciating the power of the three level architecture. This question focuses specifically on the ability to change the conceptual schema without impacting external schemas or application programs.

Given Data / Assumptions:

• The conceptual schema describes the logical structure of the entire database.
• External schemas describe individual user views and application perspectives.
• The question asks about changing the conceptual schema while keeping external schemas and programs unchanged.
• Standard DBMS theory defines physical and logical data independence with distinct meanings.

Concept / Approach:
Logical data independence refers to the capacity to change the conceptual or logical schema without forcing changes in external schemas or application code. Examples include adding a new attribute to a table, splitting a table into two logically related tables, or defining new relationships. As long as the external views remain consistent, applications built on those views can continue to work. Physical data independence, in contrast, refers to changing internal storage structures without affecting the conceptual schema, such as reorganizing files or changing indexing strategies.

Step-by-Step Solution:
Step 1: Recall that logical data independence deals with changes at the conceptual level.Step 2: Recognize that the question explicitly mentions changing the conceptual schema.Step 3: Note that external schemas and application programs should not need to change.Step 4: Match this description to the definition of logical data independence.Step 5: Conclude that the correct answer is logical data independence.

Verification / Alternative check:
Imagine a database where you add a new column to a table or define a new relationship between existing tables. If user views and application queries do not use these new elements, they should continue to function without modification. This demonstrates logical data independence in practice. By contrast, if you change the way records are stored on disk, but keep the conceptual schema unchanged, that would showcase physical data independence instead.

Why Other Options Are Wrong:
Option A, physical data independence, is about changing internal storage structures without altering the conceptual schema, so it does not match the scenario described in the question. Option C, both physical and logical data independence, is too broad and does not specifically answer the question, which clearly targets changes at the conceptual level. Option D, no form of data independence, is incorrect because such independence is a fundamental goal of DBMS design, not an impossibility.

Common Pitfalls:
A common error is to mix up physical and logical data independence, especially because both involve the word independence. Students sometimes assume that any independence between levels is the same, but the levels being separated are different in each case. Another pitfall is to forget that applications usually interact with external schemas or views, not directly with the conceptual schema, which is why logical data independence is so valuable. Keeping the definitions clearly separated helps in answering exam questions accurately.

Final Answer:
The ability to change the conceptual schema without changing external schemas or application programs is called Logical data independence, which corresponds to option B.