Objects in the MIB are defined using a subset of Abstract Syntax Notation One (ASN.1) called "Structure of Management Information Version 2 (SMIv2)" RFC 2578.
The database is hierarchical (tree-structured) and each entry is addressed through an object identifier (OID).
ASN.1 is a joint ISO and ITU-T standard, originally defined in 1984 as part of CCITT X.409:1984.
The MIB hierarchy can be depicted as a tree with a nameless root, the levels of which are assigned by different organizations.
It enhances and adds to the SMIv1-specific data types, such as including bit strings, network addresses, and counters.
MIB modules are occasionally updated to add new functionality, remove ambiguities and fix defects.
An example of a MIB module that has been updated many times is the important set of objects that was originally defined in RFC 1213, also known as "MIB-II".
This MIB module has since been split up and can be found in MIB modules such as RFC 4293 "Management Information Base for the Internet Protocol (IP)", RFC 4022 "Management Information Base for the Transmission Control Protocol (TCP)", RFC 4113 "Management Information Base for the User Datagram Protocol (UDP)", RFC 2863 "The Interfaces Group MIB" and RFC 3418 "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)".