# Time-Based Signals vs. Event Sequences

- Event sequences:
*x*:*Naturals*_{0}→*Symbols*

- Discrete-time signals:
*x*:*Naturals*_{0}→*Reals*^{K}*x*:*Integers*→*Reals*^{K}

- Continuous-time signals:
*x*:*Reals*+ →*Reals*^{K}*x*:*Reals*→*Reals*^{K}

The difference between event sequences and discrete-time signals is largely
one of interpretation: what is meant by the index in the domain? Time or just
ordering? Also, time-based signals more commonly have values in *Reals^{K}*
for some natural number

*K*.

**Hybrid systems** combine time-based signals with event sequences.