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resource being monitored. The subclasses define the 
particular set of counter and gauges that are applicable 
to a particular type of resource. Gauges give 
instantaneous measures of some quantity. Each type of 
resource being monitored may have a distinct set of 
counters and gauges that apply only to that type of 
resource. 
Reporting of Scheduled Statistics. A complete 
performance monitoring system deals with not only the 
collection and storage of performance data but also how 
the data is reported. The system can simply use a 
command to read the attribute values of the relevant 
instances of current data, performance event record and 
history data. 
Reporting of threshold Crossings. The performance 
data is saved at the end of the interval or reported at 
some scheduled point in time. In many cases, it is 
desirable to notify the administrator immediately when 
some event occurs. Managed objects of threshold data 
contain the thresholds and hysteresis levels associated 
with the counters and gauges of current data. If a 
counter or gauge in the current data passes a threshold, 
a notification is issued. The managed object instances 
of current data and managed object instances of 
threshold data are related by a relationship. This 
relationship is used to allow for different ways of using 
thresholds. Changing the threshold affects the 
monitoring of many managed object instances. 
6.3 Application 
The information of performance monitoring can be 
used to complete performance management of rural 
land system. The performance management 
functionality is broken down into different functional 
units (Balzer, et al., 1982). Functional units represent 
sets of capabilities and provide a way for the central 
system and rural land element to inform each other of 
which uses they can support. Various functional units 
are supported by the model. The only additional object 
classes required for performance monitoring would be 
subclasses of current data, threshold data, and possibly 
an event forwarding discriminator. 
In this scenario, the managed object instances of 
current data will be created by the element. For each of 
the resource, such as rural land and soil being 
monitored, the element would instantiate an 
appropriate managed object of current data. The 
instance of current data would be contained within the 
managed object representing the resource. The element 
selects the options such as the performance summary 
interval and set of counters and gauges. The current 
data object instances would point to one or more 
threshold data objects that define the conditions 
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
causing the spontaneous performance reports to be 
issued. 
7. MONITORING IMPLEMENTATION 
Performance monitoring information in rural land 
system describes the status and events associated with 
an object or a group of objects under scrutiny. Such 
information can be represented by individual status and 
event reports. 
7.1 Events 
Managed object can be defined not only as a 
representation of a managed resource but also as part of 
the performance monitoring system. The status of an 
object is a measure of its behavior at a discrete point in 
time and is represented by the current values of a set of 
status variables contained within a status vector. An 
event is an atomic entity that reflects a change in the 
status of an object. The status of an object has a 
duration in time; an event occurs instantaneously. 
Three kinds of events are of interest in the monitoring 
system as the followings. 
(1) A control-flow event represents a control activity 
and is associated with a control thread. 
(2) A data-flow event occurs when a status variable is 
changed or accessed. 
(3) Process-level events show the creation and deletion 
of processes. They describe the interactions and data 
flow between processes. 
7.2 Interfaces 
The interface of a managed object can be divided into 
two part as the followings. 
(1)An operational interface supports the normal 
information processing operations, fulfilling the 
main purpose of the service provided by the object. 
(2)A management interface supports performance 
monitoring and control interactions with the rural 
land management. 
7.3 Information Generation 
Monitoring information is generated by object 
instances, where software or hardware probes or 
sensors detect events or generate status and event 
reports. À sequence of such reports is used to generate a 
monitoring trace. 
Status Reporting. Status reports contain subsets of 
values from the status vectors and may include other 
related information such as time stamps and object 
identities. Status reporting criteria define which 
reporting scheme to use, what the sampling period is, 
and the contents of each report. 
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