This chapter reviews the way in which the Systems Management
Reference Model addresses the goals and requirements defined in
Portability is the ability to create software that is portable in source code form between systems from different vendors. The provision of XSM-conformant interfaces is the means by which this is achieved.
The scope of XSM interfaces is limited to management aspects. Thus XSM is a component of the wider environment required to achieve portability. Other components are provided by the X/Open Common Applications Environment (CAE).
The Resources that a Manager can manage and a Managed Object can support are determined by the software implementing those roles. XSM also specifies that there are certain Managed Objects which can always be assumed to be present in an XSM-conformant environment. The existence of these objects is an aid to software portability.
Interoperability is the ability of systems and components from different vendors to share and exchange management information. This extends beyond connectivity, since it requires a common understanding of the significance of the information.
XSM, in defining a Communications Service to be used for management purposes, provides the means for management information to be exchanged between systems. This provides the basic capability for a Manager to interact with a Managed Object.
XSM, in defining (or making reference to) particular standards for management interactions, will greatly improve the interaction between Managers and Resources.
XSM provides guidance on how Resources should be expressed as Managed Objects, and further specifies how the definition of Managed Objects is to be stated. This therefore provides a means by which a Manager on one system can understand the definition of a particular Managed Object on any given system.
Object-oriented techniques used for defining Managed Objects allow the refinement of Managed Objects whilst still providing their management according to their original definition. This aids interoperability, since it removes the need for a Manager to always understand the most up-to-date Managed Object definition for any given Resource.
The use of a model based on object-oriented technology, and in which managed Resources are represented by Managed Objects provides considerable support for transparency. Several aspects of transparency are summarised below:
These many aspects of transparency all serve to simplify the task of developing management applications. Particularly in the domain of management, it is important that transparency be selective, as there will inevitably be occasions when it is necessary to be aware of the precise location or implementation of a Resource. These occasions will normally arise at times of serious failure of aspects of the infrastructure. An example is the failure of the name service. The location of the name server must be known in order to re-start the service.
Extensibility is the ability to extend the management system and to customise it to implement differing management policies. The key areas of this are the introduction of new Resources to manage and the introduction of new ways to manage them. In addition, new services and support for new protocols may be provided.
The way in which Resources are specified as Managed Objects is one key aspect of the ability to extend the manageability of the Resource. From the rules laid down for the definition of Managed Objects, their definition can be extended by the definition of further objects that are refinements of the original objects. These new objects may be capable of being used as if they conformed to the original definition, this capability being dependent on the implementation of the Managed Object or the managing software. In this way Managers that know of the original definition would continue to be able to manage Resources even when the definition of the Managed Objects has been enhanced to allow other Managers to manage the Resource in some other way.
The Reference Model provides a mechanism by which it is possible to extend the capabilities of the management system. Extension in this way need not be connected with the definition of additional Managed Objects, but can represent a different way of using existing Managed Objects. This could be used, for example, to provide varying styles of interface that might facilitate the porting of management software developed for other operating environments.
XSM provides that Managers can make use not only of the services provided as part of an XSM-compliant environment, but also the facilities provided by other Managers. Such a capability is, of course, dependent on the ability of a particular Manager to provide facilities in a way that is suitable for such use, but is fully catered for in XSM. It is hence possible to envisage the provision of management capability with increasing sophistication, with users free to choose the level at which they wish to manage their systems. At the same time they will be able, at a later date, to use more sophisticated management as it becomes available or the need for it is appreciated.
The availability of Managers that can manage Resources modelled as Managed Objects is not limited by XSM but only by the ingenuity of suppliers to provide such Managers. The way in which an Administrator wishes to see and identify Resources is dependent on the perception of that Administrator, both of the Resource and their role. Applications will become available that conform to these perceptions, enabling particular management policies to be implemented.
The ability of a Manager to manage a multiplicity of objects is not inherently constrained by XSM. This applies both to the number of classes that can be managed and also the number of instances of Managed Objects. With respect to the proliferation of classes, it should be noted that the addition of new classes does not mean that existing Managers will no longer be able to manage an object because its Managed Object model has been enhanced. Location transparency provides a means by which a Manager can be assisted in managing large numbers of instances of Managed Objects, since location information does not need to be obtained and retained by the Manager.
Robustness is the ability of the management system to provide the necessary levels of security and reliability.
XSM will address the provision of security in the relationship between the Manager and the Managed Object, by the provision of suitable services. This ensures that the Manager can be assured that the Managed Object with which it is communicating has the identity it claims to have, and that the communications with it cannot be corrupted. Likewise, a Managed Object can ensure that it only accepts requests from a Manager who has the authority to make such a request, and that it will supply information only to Managers that have the appropriate level of authority.
Hence, provision of authorisation and authentication services for the Manager and Managed Object comes within the scope of XSM. However, ensuring that the Manager and Managed Object use the security functions (mandatory security) is not covered by XSM, being the province of local procedures and/or other standards.
As has been stated, a Managed Object may interact with many different Managers and XSM does not define how, where several Managers manage a single Managed Object, consistency of the Managed Object as viewed by a particular Manager is achieved. The interaction between two or more Managers which would be necessary to ensure consistency, is outside the scope of XSM.
XSM provides for both confirmed and unconfirmed management interactions. When confirmed interactions are used, the initiator can be informed of the status of the requests it has initiated. Using this facility, Managers and Managed Objects can be assured of the success of operations they have requested, so improving the reliability of the management system.
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