Definition: an AS event is a variation of (splice) sites between common sites, or the respective transcript ends. An AS event contains at least one alternative splice site, i.e. a splice site that is transcribed by multiple transcripts but not used by all of them.

Definition: an internal AS event is flanked to both sides (i.e., at its 5'- and 3'-end) by common sites between the compared transcripts, and does therefore not involve alterntative transcription start

Definition: an external AS event involves beside alternative splice site(s) also variability in the 5'- and/or 3'-end of the transcript

Definition: an additional splicing event is not an AS event, because it does not contain a single alternative splice site–a splice site present in multiple transcripts but not used in all. However, an additional splicing event shows splice sites used by some and not by other transcripts, however, these splice sites do not fall within the common transcribed area.

Definition: a variable sites event does not contain any variable splice site, alternative or additional. However, it describes variations in the 5'-start and/or 3'-end of transcripts that overlap.