Constructed ASN.1 types

Constructed types are those that combine similar or different primitive types into ordered or unordered groups. VTAM® CMIP services represents the members of constructed types by enclosing the members in parentheses. There are four constructed types. Whether a type can contain members of different types and whether order is important depends on the constructed type.

Table 1. Order and members of constructed types
Constructed type	Members	Order
SET	Members can be different types.	Order of members is not important.
SEQUENCE	Members can be different types.	Order of members is important.
SET OF	All members must be the same type.	Order of members is not important.
SEQUENCE OF	All members must be the same type.	Order of members is important.

The hexadecimal BER format can also be used for constructed types. When the hexadecimal BER format is used, either the members of the constructed type can be specified as BER or the entire contents of the SET or SEQUENCE can be specified in a single value. For example, given the following ASN.1:

A ::= SEQUENCE
{
    a INTEGER,
    b INTEGER,
    c INTEGER
}

any of the following values may be specified:

(a 1, b 2, c 3)
(a <01>, b <02>, c <03>)
<020101020102020103>

The former value specification is preferred, because CMIP services can check that the values that are specified are valid and CMIP services can construct the correct encoding of the tags, lengths, and values.