In Koda Kumi's song Birthday Eve I found ダーレン, which means darling. In the yellowbook, it introduces that katakna are used to write foreign names and loan words. I think by using katakana, people could easy distinguish words that are from their original language or are imported from other countries. In Ayumi Hamasaki's song Boys and Girls I found the word イイヒト, meaning good person. I didn't realise that it is something we've learnt before, いいひと. It could have been written in hiragana and kanji, but here the author uses katakna, I think it's for emphasis . Among all the hiragana and kanji words, a katakana word looks very different, I guess that's why they use katakana to gain people's attention and then to emphasis what the word means.
In our yellow book, the introduction of katakana is quite simple:
Katakana are used to write foreign names and loan words. While in the other textbook, it talks about how Katakana looks different from Hiragana, also in what cases they're used and why people tend to use it. I think in our yellowbook the author mainly want to tell us the basic knowledge of katakana, but the other textbook focus on the cultural background behind Japanese writing system and thus help us to have a deeper perspective of it. For example, it introduces that in fashion magazines and advertisements and among young urbanites they prefer to use katakana more even though there's a perfect native Japanese word exists. I guess maybe in this more and more globalised world, Japan is open to absorb different kinds of language and culture, and young generation in Japan are very modern!