The topics subordinate to this one give an overview of the simple types, by kind.
As shown there, some simple types are expressed with parameters. For example, Decimal is a numeric type and can be restricted by parameters that define a second numeric type such as Decimal(4).
With one exception, the following rule applies: If a simple type can be expressed with parameters, the non-parameterized type such as Decimal is a reference type, and the parameterized type such as Decimal(4) is a value type. The one exception is String and its parameterized equivalent. Both String and String(4) are reference types.
Here are the reference topics:
The types are BYTES, CHAR, DBCHAR, HEX, MBCHAR, STRING, and UNICODE.
The types are DATE, INTERVAL, TIME, and TIMESTAMP.
The types are BLOB and CLOB.
The types are BIGINT, BIN, FLOAT, INT, MONEY, NUM, NUMC, NUMBER, PACF, SMALLFLOAT, and SMALLINT.