Wow, you even studied linguistics...
Well, /ɪ/ is the vowel in TIP, and /aɪ/ is the diphthong in TYPE. The symbol /i/ technically stands for a higher vowel, as in TEA, for example. That's IPA.
SAMPA is another transcription method where only ASCII characters are used (so you can find them on your keyboard). This is SAMPA for English:
http://en.wikipedia.org/wiki/SAMPA_chart_for_EnglishUsing SAMPA you write the schwa as @, and you don't need "strange" symbols that are not on your keyboard. Marvin used SAMPA.
PS: I prefer IPA. I never learned SAMPA decently
