ogging). Thus, a managed object is the abstraction of such a resource that represents its properties as seen by (and for the purposes of) management. A managed object may also represent a relationship between resources or a combination of resources (e.g., a network). It must be noted that object-oriented principles apply to the information modeling, that is, to the interfaces over which communicating management systems interact and should not constrain the internal implementation of the telecommunications management system. 8.3.3.1.3 TMN Physical Architecture The physical architecture consists of building blocks and each building block can contain multiple functional blocks as shown in Table 8.2. The building blocks are: Operations System (OS) performs operations systems functions including operations monitoring and controlling telecom management functions. The os may optionally provide some of the mediation, Q-adaption and WS functions. Mediation Device (MD) is the device which performs mediation between local TMN interfaces and os information model. The MD may also optionally provide OSFs, QAFs and WSFs. MDs can be implemented as hierarchies of cascaded devices. Q Adapter (QA) is a device which connects NE-like or OS-like with non-TMN compatible interfaces (at m reference points) to Qx or Q3 interfaces. In simple terms, the QA translates between TMN and non-TMN interfaces. For example, a TL1 Q-adapter translates between a TL1 ASCII message-based protocol and the CMIP, the TMN interface protocol; likewise, SNMP Q-adapter translates between SNMP and CMIP. Data Communication Network (DCN) is a communication network within a TMN which supports the DCF. The DCN represents an implementation of the OSI layers 1-3, which include any relevant ITU-T or ISO standards for layers 1-3. The DCN provides no functionality at layers 4-7. Table 8.2 Relationship between building and functional blocks [25] (Notes 2 et 3) O (Note 3) Mandatory Optional Notes: 1 Within this table, where more than one name is possible, the choice on th