In computing, an object identifier or OID is an identifier used to name an object (compare URN). Structurally, an OID consists of a node in a hierarchically-assigned namespace, formally defined using the ITU-T's ASN.1 standard, X.690. Successive numbers of the nodes, starting at the root of the tree, identify each node in the tree. Designers set up new nodes by registering them under the node's registration authority. The root of the tree contains the following three arcs:
- In computer security, OIDs serve to name almost every object type in X.509 certificates, such as components of Distinguished Names, CPSs, etc.
- Within X.500 directory schemas and protocols, to uniquely name each attribute type and object class, and other elements of schema.
- Within LDAP schemas, each object class and each attribute type has a unique OID
- In computer networking, an OID, in the context of the Simple Network Management Protocol (SNMP), consists of the object identifier for an object in a Management Information Base (MIB).
- HL7, DICOM and other health care related information interchange standards use OIDs for globally unique identifiers for both individual information objects as well as References to code systems and data element dictionaries. DICOM uses the term UID (Unique IDentifier) in place of OID.
- The IANA OID registry contains a list of registered entities that use OIDs to reference internal structures (e.g. directory attributes). Each entity is assigned an initial referential value (e.g. 184.108.40.206.4.1.5518 for TDS Telecom Inc.) and thereafter the internal numbering plan is up to the entity to define (e.g. 220.127.116.11.4.1.5518.104.22.168 might refer to the "CCID" attribute of the LDAP directory associated with customers). This allows for precise referencing of data attributes in a company or other entity.
Another increasingly used form[when?] of OID is in the area of health care and public health informatics in the United States. Health Level Seven (HL7), a standards-developing organization in the area of electronic health care data exchange, is an assigning authority at the 2.16.840.1.113883 (joint-iso-itu-t.country.us.organization.hl7) node. HL7 maintains its own OID registry, and as of January 1, 2008 it contained almost 3,000 nodes, most of them under the HL7 root. The Centers for Disease Control and Prevention has also adopted OIDs to manage the many complex values sets or "vocabularies" used in public health. The various OIDs are available in the Public Health Information Network (PHIN) Vocabulary Access and Distribution System (VADS).
See also 
- Digital object identifier
- International Geo Sample Number
- Surrogate key
- Extended Validation Certificate
- Universally Unique Identifier
- Globally Unique Identifier
- Uniform Resource Name
- Persistent Object Identifier
- In computer programming, an object identifier generally takes the form of an implementation-specific integer or pointer that uniquely identifies an object. However, OIDs are a specific approach to creating globally unique object identifiers in a distributed system.
- OBJREFs have an object identifier (OID) field.