What is a primary key? Explain two importances of a primary key. Give a chronological order which dry-run testing is performed when developing a program.

Here are the solutions to the questions:

1. a) What is a primary key? A primary key is a column or a set of columns in a database table that uniquely identifies each record (row) in that table. It ensures that no two records have the same primary key value.

   b) Explain two importance of a Primary Key in a database:

   • Ensures Data Integrity: A primary key guarantees that each record is unique, preventing duplicate entries and maintaining the accuracy and consistency of data within the table.
   • Establishes Relationships: It serves as a crucial link to create and manage relationships between different tables in a relational database, allowing data to be combined and queried efficiently across multiple tables.

2. Give a chronological order which dry-run testing is performed when developing a program: Dry-run testing is typically performed in the following chronological order:

   • After Algorithm Design: It is done once the program's logic or algorithm has been designed, often represented by flowcharts or pseudocode.
   • During/After Code Writing: It is performed manually by tracing the code line-by-line with sample data before the program is compiled or executed on a computer.
   • Before Formal Testing: It serves as an initial check to identify logical errors and design flaws early, reducing the need for extensive debugging during later stages of formal testing.

3. State three situations where processing modes can be categorized: Processing modes can be categorized based on how and when data is handled. Three common categories are:

   • Batch Processing: Data is collected over a period and processed together in large groups or "batches" at a scheduled time.
   • Real-time Processing: Data is processed immediately as it is input, providing instant feedback or updates, often critical for time-sensitive applications.
   • Online Processing: Data is processed interactively as it is entered by a user, typically through a network connection, allowing for immediate interaction with the system.

4. Given the binary number 101011011011, determine the number of: The given binary number is 101011011011. First, count the total number of bits: There are 12 bits in the number.

   a) nibbles
   A nibble is a group of 4 bits.
   Number of nibbles = $\frac{\text{Total number of bits}}{\text{Bits per nibble}}$
   Number of nibbles = $\frac{12}{4} = 3$
   The number of nibbles is $\boxed{\text{3}}$.

   b) bytes
   A byte is a group of 8 bits.
   Number of bytes = $\frac{\text{Total number of bits}}{\text{Bits per byte}}$
   Number of bytes = $\frac{12}{8} = 1.5$
   The number of bytes is $\boxed{\text{1.5}}$.