Keywords often represent compact representations of contents of a document. Keyword acquisition can be done in two ways

• keyword assignment
• keyword extraction

Keyword assignment means that keywords are chosen from a controlled vocabulary of terms or predefined taxonomy.

Keyword extraction selects the most representative words explicitly presented in the document, which is independent from any vocabulary.

Keyword enhanced NLG are categorized into

• Incorporate keyword assignment into text generation
• Incorporate keyword extraction into text generation