A Level Computer Science OCR Practice Exam

Dictionary encoding is also known as what?

1. Substitution coder

2. Run-length coder

3. Asymmetric encryption

4. Data compression

The correct answer is: Substitution coder

Dictionary encoding is also known as a substitution coder because it works by substituting values in the dataset for shorter representations stored in a dictionary. In this encoding technique, frequently occurring patterns or sequences in the data are replaced by codes that reference those patterns in a separate dictionary. This method efficiently reduces the amount of data that needs to be stored or transmitted, which is an essential aspect of data compression. While data compression is closely related, as dictionary encoding is a technique used within the broader context of data compression, it's not the term used specifically to refer to dictionary encoding itself. Additionally, run-length coding involves compressing data by replacing sequences of repeated data with a single data value and a count, which is distinct from how dictionary encoding operates. Asymmetric encryption, on the other hand, pertains to the security of data rather than encoding or compressing it.