When you assess the structure of an acquired set of tables that already contain data, checking the validity of possible referential integrity constraints on foreign keys is part of which step in the evaluation process?

Introduction / Context:
When a database designer inherits an existing set of tables with data, a systematic assessment process is needed to understand the structure and quality of that data. This process usually proceeds in several ordered steps, starting with simple observations and moving toward more detailed logical analysis. One part of this assessment is to check whether the assumed foreign keys and their referential integrity constraints are actually valid for the existing rows. This question asks at which step of that multi step assessment process this referential integrity validation typically occurs.

Given Data / Assumptions:

We are dealing with an acquired set of tables that already contain data, perhaps from a legacy system.
An assessment process with several ordered steps is being followed to understand and normalize the table structure.
Possible foreign key relationships between primary tables and secondary tables have been identified or hypothesized.
The validity of referential integrity constraints means that every foreign key value matches an appropriate primary key value in the referenced table, or is null when allowed.
We are interested in which numbered step of the process includes this validation.

Concept / Approach:
A common four step approach to assessing acquired tables is as follows. In the first step, the designer counts rows, examines column names, and gets a basic feel for the data. In the second step, the designer identifies candidate keys and primary keys in each table. In the third step, the designer examines potential foreign keys and checks whether the assumed referential integrity constraints hold for the existing data. In the fourth step, the designer refines normalization and considers splitting or merging tables based on the discovered dependencies and constraints. By mapping this general approach to the options, we can identify the correct step number for the referential integrity validation activity.

Step-by-Step Solution:
Step 1: Recall that early in the assessment, the focus is on simple structural facts such as the number of rows, the presence of obvious duplicates, and initial candidate keys. This is typically described as the first and second steps. Step 2: After basic keys are understood, the next logical step is to look for relationships between tables. This involves identifying columns that might be foreign keys referencing primary keys in other tables. Step 3: Once potential foreign keys are identified, the designer must test whether every foreign key value actually matches a primary key value in the referenced table. This is what is meant by checking the validity of possible referential integrity constraints on foreign keys. Step 4: In the standard sequence used in many normalization discussions, this referential integrity validation is treated as part of the third step of the assessment, after basic keys are identified but before more advanced restructuring decisions are made.

Verification / Alternative check:
To verify this ordering, imagine that you try to validate referential integrity constraints before you even know which columns are candidate keys or primary keys. That would be difficult and unreliable because you would not yet know which columns in the referenced table should be matched. Conversely, if you postpone referential integrity checks until after full restructuring, you risk making design decisions based on incorrect assumptions about relationships. This supports the idea that referential integrity validation naturally follows the identification of keys and therefore belongs in the third step of the assessment process.

Why Other Options Are Wrong:
The first step is too early, as at that stage the designer usually performs basic profiling such as counting rows and inspecting column names, but does not yet have enough knowledge about keys and relationships.
The second step typically focuses on determining primary keys and perhaps some candidate keys within each table, rather than inter table relationships, so full referential integrity validation is not yet performed.
The fourth step is too late in the process, because by then many normalization and restructuring decisions should already have been made, and those decisions depend on having accurate information about foreign key validity.

Common Pitfalls:
One pitfall is to assume that foreign key constraints are already correct just because the system has been running in production, without checking existing data for violations. Another mistake is to guess foreign key relationships based on column names alone and then enforce constraints without validating them, which can cause errors when constraints are applied. Designers also sometimes forget that legacy systems may have incomplete or inconsistent enforcement of referential integrity, so explicit validation queries are an important part of the assessment. Following an ordered multi step process helps ensure that referential integrity is checked at the right time and with sufficient information.

Final Answer:
Checking the validity of possible referential integrity constraints on foreign keys is part of the third step in assessing an acquired set of tables with data.