Figure A-8 Example of Use of Refined NIST metrics model to represent response time metrics

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Figure A-8 Example of Use of Refined NIST metrics model to represent response time metrics : Object diagram

Created:	5/10/2022 1:16:55 PM
Modified:	6/4/2022 3:05:06 PM
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Author:	Natha Paquette
Version:	1.0.0
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ID:	{D1D5ECAF-D5E7-46ef-88BE-67091FEBB24D}

Figure A-8 is an example of object instances following the refined model in Figure A-7, representing an example of the actual specification of some response time metrics. The ultimate goal of this work is to specify a set of templates which can be used to define actual Cloud Computing metrics. Comparison of the Metric Models This section describes how each of the Models summarized in the preceding sections represent concepts regarding Metrics and their evaluation. They present a high-level view of the differences between these models. Representing kinds of target for a metric definition In OMG SMM the Scope class has a pointer to a single named class in the MOF metamodel for the target system. NIST Metrics Model has an attribute targetCharacterization in ContextCondition class. However, the NIST Metrics model does not assume a model for the target systems is available. In TM Forum SID Metrics, the relationships between MetricDefinition and RootEntityType and Specification convey the target for a Metric. SMM Scope is not restricted to a single class from the underlying system model. OSI Systems Management Metric Objects are installed at run time, and there is no restriction to what classes of Managed object can be observed by a Metric Object. Binding a measurement to a specific target for a single metric evaluation In OMG SMM the Measurement class has a pointer to a single MofElement instance in the target system. The NIST model currently only specifies definitions applicable to use in Metric templates. There are no pointer attributes in the Measure class (to be renamed MeasurementResult) to indicate the run time target for the Metric evaluation. The TM Forum SID Metrics model has an association "MetricCollectedFor" from Metric class to RootEntity class. This can point at an instance of any element defined in the model for the target system. OSI Systems Management MonitorMetric and its subclasses have a pointer to the observed managed object instance, and its attribute being observed. Periodic scanning of a target by a Metric This is the primary purpose for the OSI Systems Management Metric Objects. The MonitorMetric class has a granularity period for subsequent scans (using a get operation) of attribute values of Observed managed objects. The MeanMonitorMetric class has an attribute to specify the moving time period over which the estimate is calculated. The metric objects also have optional attributes to specify scheduling of when the Metric object is enabled to scan. OMG SMM and TM Forum SID metrics model are static in nature. The assumption is that the Metric will be evaluated for the state of the system at the time of observation. Neither of these models specifies facilities for evaluating statistical quantities over time. The NIST Metrics model is also a static model. The concept of periodic scanning of resource attributes is not currently supported. There is no way specified to force a measurement to be taken using a periodic test stimulus. The examples assume measurements will be taken upon natural stimuli (i.e., not driven by a test driver). However, the group is investigating how statistical quantities (such as mean and variance) can be evaluated from a set of measurement results taken on a single target over some time interval (e.g., calculating a mean response time for a target over a time period using all available response time measurements taken for that target over that interval). Representation of a metric Measurement result OMG SMM has the Measurement class to represent the result of a measurement. NIST Metrics model currently has the Measure class to represent the result of a measurement. However, the NIST WG is considering changing the name of this class to MeasurementResult, to avoid confusion. TM Forum metrics model has the Metric class to represent the result of a measurement. OSI Systems Management Metric Objects have a derivedValue attribute in the MonitorMetric class which stores the current value associated with the Metric. The subclasses also add attributes for the estimate of the statistical quantity taken over a Moving Time Period. Representation of a metric Measure Definition OMG SMM has the Measure class to specify the definition for a measurement. NIST Metrics Model has the MeasureDefinition class to specify the definition for a measurement. TM Forum metrics model has the MetricDefinition class to specify the definition for a measurement. OSI Systems management does not allow arbitrary measurement definitions. The behavior of the Metric objects is restricted to operations over time on observed attributes, and is hard coded into the behavior definitions for the Metric objects. Representation of composite metric measures definitions and measurement results The OMG SMM specifies: <ul>
<li>A BinaryMeasure class which evaluates a binary operation (e.g., +, -, /, *) on the values of two other Measures. More complicated combination operations need to be expressed by breaking the calculation into a series of binary operation steps.</li><li>A CollectiveMeasure class which evaluates an accumulation operation (sum, min, max, mean, standard deviation) over a set of entities which are involved in a similar relationship with a scoped class.</li><li>No other forms of calculating composite metrics are specified.</li></ul>
In the NIST Metrics model a primary MeasureDefinition can be composed using underlying MeasureDefinitions and an expression in the primary MeasureDefinition). In the TM Forum Metrics model, a MetricDefinition can be composed using other MetricDefinitions through the use of MetricDefinitionMethodArgument. OSI Systems management Metric Objects has no facilities to compose multiple metrics.