This section points out a few "gotchas" that exist within the CIM infrastructure. It is not meant to be exhaustive but rather to focus on small points which may be important in building a model: actually places where I have tripped over a point of detail when building a model.
Be aware of whether to define a particular entity as a class or as an instance. Superficially you may feel that the distinction is obvious, but consider a 56 kbps dial-up modem from the ABC Manufacturing Company with model number 23/567AB. The DMTF provides a description of a generic dial-up modem in its Device Common Model ”see Figure 10.1 ”so you might consider creating a new class called something like ABC_Type23567AB_Modem and making it a subclass of CIM_POTSModem.  This would probably be wrong! Although there are pathological cases where it would be better to model it as a subset of a CIM_POTSModem, your 23/567AB, 56 kbps modem from ABC Manufacturing is almost certainly an instance of (rather than a subset of) a CIM_POTSModem.
 The acronym POTS stands for "plain old telephone system" and a POTS modem is one which works by using in- band tones across a standard telephone line rather than a cable modem or an ADSL modem.