The SYNTAX clause, which must be present, defines the abstract data structure corresponding to that object. The data structure must be one of the following: a base type, the BITS construct, or a textual convention. (SEQUENCE OF and SEQUENCE are also possible for conceptual tables, see section 7.1.12). The base types are those defined in the ObjectSyntax CHOICE. A textual convention is a newly-defined type defined as a sub-type of a base type .
A extended subset of the full capabilities of ASN.1 sub-typing is allowed, as appropriate to the underingly ASN.1 type. Any such restriction on size, range, enumerations or repertoire specified in this clause represents the maximal level of support which makes "protocol sense". Restrictions on sub-typing are specified in detail in Section 9 and Appendix C of this memo.
The semantics of ObjectSyntax are now described.