s the net- work level structure of an AMLn model (as discussed in Sect 3.1). According to this structural feature, an AMLn model will normally be partitioned into a number of model fragments that (in the complete model) are related over substructure rela- tions. Fragments on higher network levels are candidates for high level MOs, as depicted in Fig. 5.18. Here we have aligned the TMN functional level view to net- work levels. The top three network levels (0..2) cover what normally is standardized, and therefore would be candidates for standardized MOs. Implementors may refine these fragments further into any number of lower network levels (taken as a basis for proprietary MOs defined by implementors). Each fragment is a "small" AMLn model, i.e., described by a layer structure and a logical network structure. Therefore, for any particular network level, the frag- ment can be taken as the basis for at least two network MOs, one for its layer struc- ture, another for its logical network structure. Following the TMN classification, we may separate NW-MOs into EM-MOs and NM-MOs. For every NW-MO, a number of network element MOs (NE-MO) can be identified, specified and imple- mented. 7 In this section we discuss the potential of AMLn models in network management, presenting some ideas about how such models can be used in that context. Actual applications of NW-- MOs in management systems cannot be presented in this book (but hopefully in a later book). 5.5 Using AMLn Models in Management Systems An AMLn model Managed objects (in abstract object structures) NW-MOs (volatile) NE-MOs (static) Imple- mentor's models Fig. 5.18 Fragments of an AMLn model are candidates for managed objects. EM=network-ele- ment manager; MO=managed object; NE=network element; NL =network level; NM=network manager Note that the role of a network MO is to translate operations on the very MO to invocations on lower level MOs, which normally will be MOs in one or several NEs (i.e., NE-MOs), but could be operations as well on one or several MOs in 