What are the importance of primary keys and dry-run testing, and list three electronic data processing modes?

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 must contain unique values for each record and cannot have null values.

• Uniqueness and Identification: A primary key ensures that every record in a table can be uniquely identified, preventing duplicate entries and maintaining data integrity.
• Establishing Relationships: Primary keys are crucial for establishing relationships between different tables in a relational database. They serve as foreign keys in other tables, linking related data.

Dry-run testing is performed before the program is actually executed on a computer. It is typically done by a programmer manually tracing the logic of the code with sample input data, step-by-step, to identify logical errors, design flaws, or incorrect algorithms early in the development cycle, often during the coding or debugging phase.

1. Batch Processing: Data is collected over a period and processed in groups or batches at a scheduled time.
2. Real-time Processing: Data is processed immediately as it is input, providing instant results or updates.
3. Online Processing: Data is processed interactively, often through a network, allowing users to directly interact with the system and receive immediate responses.

• Data Collection refers to the broader process of gathering raw facts and figures from various sources, such as surveys, observations, or existing documents. It's about obtaining the initial data.
• Data Capture is the specific process of converting the collected raw data into a machine-readable format that can be directly input into a computer system for processing. This often involves using input devices like scanners, keyboards, or sensors.