An instance of class OM_C_EXTERNAL is a data value and one or more information items that describe the data value and identify its data type. This class corresponds to ASN.1's External type, and thus the class and the attributes specific to it are described indirectly in the specification of ASN.1. (See Clause 34 of Recommendation X.208, ''Specification of Abstract Syntax Notation 1 (ASN.1),'' CCITT Blue Book, Fascicle VIII.4, International Telecommunications Union, 1988. Also published by ISO as ISO 8824.)
This class has the attributes of its superclass, OM_C_OBJECT, in addition to the OM attributes specific to this class that are listed in the following table.
Attributes Specific to OM_C_EXTERNAL
| Attribute |
Value Syntax | Value Length | Value Number | Value Initially |
| OM_ ARBITRARY_ ENCODING |
String(OM_S_ BIT_STRING) |
- | 0 or 1 See Note 19 |
- |
| OM_ASN1_ ENCODING |
String(OM_S_ ENCODING_ STRING) |
- | 0 or 1 See Note 19 |
- |
| OM_DATA_ VALUE_ DESCRIPTOR |
String(OM_S_ OBJECT_ DESCRIPTOR_ STRING) |
- | 0 or 1 | - |
| OM_DIRECT_ REFERENCE |
String(OM_S_ OBJECT_ IDENTIFIER_ STRING) |
- | 0 or 1 | - |
| OM_INDIRECT_ REFERENCE |
OM_S_ INTEGER |
- | 0 or 1 | - |
| OM_OCTET_ ALIGNED_ ENCODING |
String(OM_S_ OCTET_ STRING) |
- | 0 or 1 See Note 19 |
- |
This attribute is a representation of the data value as a bit string.
· OM_ASN1_ENCODING
The data value. This attribute can be present only if the data type is an ASN.1 type.
If this attribute value's syntax is an Object syntax, the data value's representation is that produced by om_encode( ) when its Object parameter is the attribute value and its Rules parameter is ber. Thus, the object's class must be one to which om_encode( ) applies.
· OM_DATA_VALUE_DESCRIPTOR
This attribute contains a description of the data value.
· OM_DIRECT_REFERENCE
This attribute contains a direct reference to the data type.
· OM_INDIRECT_REFERENCE
This attribute contains an indirect reference to the data type.
· OM_OCTET_ALIGNED_ENCODING
This attribute contains a representation of the data value as an octet string.