Object Identifiers

An important data type in ASN.1 is the object identifier. An object identifier (OID) is a reference number, unique in the world, that can be allocated to, in principle, any object; in practice, to any object that can be represented as a set of information. The object identifiers form a tree structure. The branches of the tree are referred to as arcs, and various organizations have been allocated responsibility for registering OIDs by assigning nodes in particular parts of the tree to anyone who requests one, to represent particular objects.

Each node has a number, and optionally, a name. An object's OID is the list of numbers representing the nodes in the tree from the root to that object's own node. They are normally shown enclosed in braces and separated by spaces. If a node's name is shown as well, the node's number is normally shown in parentheses. Only the numbers are intended to be machine-readable - the names are there to be human-readable.