This chapter provides an introduction to concepts and notation that are treated more fully in Section II. Some of these features have been briefly mentioned already, but without a full treatment. This includes

• Object identifiers,

• Character string types,

• Subtyping,

• Tagging, and

• Extensibility, exceptions, and version brackets.

Other topics that are introduced here for the first time are

• Hole types,

• Macros,

• Information object classes and objects and object sets,

• Other types of constraint,

• Parameterization, and

• The ASN.1 semantic model.

An introduction is provided here for the reader who wishes to ignore Section II. As of mid-1999, there are no areas or concepts concerned with the ASN.1 notation that have not been at least introduced by the end of this chapter.

The aim of the text in this chapter is

• to describe the concept and the problem that is being addressed,

• to illustrate where necessary key aspects of the notational support so that the presence of these features in a published protocol can be easily recognized, and

• to summarize the additional text available in Section II.

If further detail is needed on a particular topic (if something takes the reader's interest), then the appropriate chapter in Section II can be consulted. The chapter in Section II provides "closure" on all items mentioned in this chapter unless otherwise stated.