An expression is a combination of constants, variables, random variables, functions, parentheses and operators that yields a single value. Silk Performer distinguishes among the following expressions:

- Relational expressions
- Boolean expressions
- Numeric expressions
- String expressions

The following special Silk Performer functions can be used in expressions:

- Type conversion functions (chr, ord, string, number, float)
- High-level database functions (rows, rc, eos)
- Random types (RndUniN)