item

a number, or symbolic expression representing

a single data value.

missing

a keyword representing missing data.

item..item

data grouped in a class. For example, 3..4,

designates a single data item whose value

is greater than or equal to 3 and

less than 4.

Weight(value, weight)

Weighted data.

The parameter value consists

of any of the preceding item types, and

the parameter weight is the weight associated

with this data item. For example, Weight(3..4, 10),

can be used to represent 10 entries

within the class 3..4.