ITPEC IP October 2020 Question 27
Sales data is to be managed with tables in a relational database. When the tables for sales data are designed, which of the following activities analyzes the relationship between the fields of the tables and decompose the tables so that there are no duplications or inconsistencies in the data?
Explanation
Normalization — analysing the dependencies between fields and splitting the tables so that each fact is stored only once.
If a sales table holds the product name and unit price in every sales row, the same price is repeated many times, and changing it in some rows but not others leaves the data inconsistent. Normalization finds which fields depend on which key (the product name and unit price depend only on the product code) and moves them to a table of their own, linked by that key. Each fact is then stored once and cannot contradict itself.
Answer (c)
Why not others:
- •(a) Join — combines rows of two tables through matching field values when data is retrieved; it puts decomposed tables back together rather than decomposing them
- •(b) Projection — extracts selected columns from a table in a query; an operation on data, not a design activity
- •(d) Exclusive control — locks data so that simultaneous updates by several users do not overwrite each other; it deals with concurrent access, not with duplication in the table design
Key rule: Normalization is done when the tables are designed; selection, projection and join are operations that retrieve data from them; exclusive control governs concurrent updates.
Databases · AI-written, may contain errors
This question comes from an official ITPEC past paper. ITPEC Practice is an independent study tool and is not affiliated with ITPEC. See the official IP past-paper collection or Report an issue.