2.2 Algorithm for the transformation of SNMP MIBs into the CORBA object model

  The mapping of existing management information bases to the CORBA object model implies the development of algorithms for translating the MIB specification languages. Our scenario requires an algorithm for mapping the ASN.1 template language used for the Internet MIB specifications into the OMG Interface Definition Language (IDL). Such an algorithm ([13]) has been developed by the Joint X/Open NM-Forum Inter-Domain Management Task Force (JIDM) and was recently adopted by the NM-Forum. The complexity of bridging the different information models may be illustrated as follows: Internet MIBs define the properties of an agent in terms of scalar variables and tables and have no notion of object-oriented concepts like inheritance or polymorphism. In contrast, CORBA agents are defined based on object classes and their associated attributes, methods and relationships. The transformation of SNMPv2 data types, macros and traps into the CORBA mechanisms is described below:

• Every SNMP group becomes an object class; the scalar data types contained therein are transformed into attributes of the object class. The SNMPv2 data types are mapped to their IDL counterparts, e.g. Integer32 becomes long, DisplayString and IpAddress are mapped to a sequence of octets.
• SNMP tables become object classes, too. Each table entry represents in the OMG model an instance of an object class which is described by an IDL interface. An example shows the application of this rule: If three hard disks are contained in a system, this is represented in the MIB through the existence of a table storageTable with three rows. A CORBA-compliant system would instead create three instances of an object class StorageDevice.
• Variables specifying table columns become attributes of the corresponding object class.
• SNMP traps are transformed into CORBA events which are implemented through the Object Event Service ([7]).

Although the JIDM algorithm is a powerful tool, it is necessary in our case to perform some adjustments because management semantics are often defined in the Internet information model in an implicit way: In the Internet management architecture, actions on managed objects are performed by assigning a certain value to so-called "pushbutton" variables because the SNMPv2 management protocol has no action protocol data unit. The CORBA analogy consists in calling a method of the managed object.
The translation algorithm is unable to perform this mapping because "pushbutton" variables cannot be distinguished from regular variables on a syntactic level.