I don't mean to be contrarian, but I don't think it's useful to think of ToBI as graph of pitch over time, or as using curves. We should distinguish between ToBI as a model of intonational structure, and ToBI as an annotation system. As a model of intonational structure, ToBI does not model how quickly an utterance is spoken; the only temporal information it cares about is the sequence of tones and break indices, and the alignment of those tones and break indices with the text. As an annotation system, ToBI will convey how quickly the utterance was spoken, because the tones are aligned with where the text was pronounced on the waveform.
ToBI models the tune as a sequence of tone targets, which are expressed as an opposition between high pitch and low pitch. So a L+H* pitch accent has a high target on the accented syllable, and is preceded by a low target. A H-H% boundary tone (e.g. for polar interrogatives) has a high target at the end of a prosodic phrase, and is preceded by a high target.
ToBI is also not about characterizing F0 traces. ToBI's focus is intonational structure, which it models as a shallow tree of prosodic phrases and a sequence of tones, called the tune. Remember the full name of ToBI: Tones and Break Indices. Each word boundary is associated with a break index which expresses the level of perceived juncture. Each level of juncture corresponds to the type of prosodic constituent that is ending. For example, in Mainstream American English (MAE) ToBI, a word that is followed by a break of 4 is at the end of a prosodic phrase, and a word that is followed by a break of 3 is at the end of an intermediate phrase.
To understand how this relates to F0, we should adopt the following ontology. F0 is a physical property of periodic signals. Pitch is a psychoacoustic percept that is largely a reflex of F0. Tone is the linguistic interpretation of pitch. F0 traces might do many things, but there will be ToBI tones only at pitch accents, which align with the primary stress-bearing syllable of a word (in English), and boundary tones, which occur at the ends of prosodic phrases. Prosodic phrasing, however, is correlated with many things besides F0, such as duration, syllable weight, and loudness. The tune is not just a coarse encoding of F0.
For a more detailed practical description, have a look at
the versions of ToBI developed for different languages, or
the labeling guidelines for English. For a more involved discussion of the justification for the theoretical choices, see
Beckman and Pierrehumbert (1986) or
Pierrehumbert (2000).
-- EDIT
zaba, based on your recent questions, I would really recommend carefully reading Pierrehumbert (2000) linked above. It contrasts the ToBI view with other views, clearly states and argues for the theoretical commitments (e.g. ``there is no such thing as an intonation pattern without a prosodic context''), and provides lots of concrete examples that demonstrate and justify those commitments.
