Computing in a heterogeneous environment requires an exchange of information among computers which have different ways of representing information. This type of information exchange demands a standard external data representation. One such standard, Abstract Syntax Notation One (ASN.l), is defined by the International Organization for Standardization (ISO) and its transfer syntax, the Basic Encoding Rules (BER). This project presents the design of a C++ class hierarchy modeling the concepts presented in ASN.l and encapsulating the BER encoding rules. The goal of this class hierarchy is to utilize the rich features of object-oriented paradigm to provide a clean and simple interface for OSI presentation layer protocols to application developers and implementors. This report discusses the class hierarchy in detail and shows how the primitive and constructed ASN.l types are defined, encoded and decoded using this hierarchy.