ModSnmp Manual v3.09 - 6.2. SNMP Objects
SNMP has several types of variable, and it does place interpretations on the values of the variables. For example, the types TimeTicks and Integer32 are both 32-bits in size, but have different interpretations. The OctetString type is an exception - it is specifically provided as an uninterpreted type (although it is often used to represent text).
SNMP uses a single address range for all its objects, independent of their types. The objects are addressed using OIDs (Object Identifiers), which are sequences of integers. For example, the "System Name" object is addressed using the OID "220.127.116.11.18.104.22.168.0".
SNMP distinguishes between "scalar" objects, which are individual variables, and "tabular" objects, which are groups of variables that are elements in tables. The last integer in an OID is called the "instance identifier". For tabular objects, the instance identifier is the index of the table row containing the variables. For scalar objects, the instance identifier is always zero.