Using Data-Driven Web Services › How to Create a Custom Metric Family › Create a Custom Metric Family XML File › Add the <ExpressionGroupList> Section

Add the <ExpressionGroupList> Section

Expressions tell Data Aggregator how to calculate values for attributes of items that are either defined in or related to your metric family. The expressions included in your custom metric family determine how these values display in reports and dashboard views. Expressions are included in the <ExpressionGroupList> section.

If the attributes of your metric family are table attributes, your metric family XML must include the <ExpressionGroupList> section, and an expression group is required for at least the following two related items (destination certifications):

• {http://im.ca.com/core}Item
• {http://im.ca.com/inventory}DeviceComponent

You must also define an expression group for each component defined in your custom metric family. The tags in the <ExpressionGroupList> section are as follows:

• <ExpressionGroup>—Create one of these tags for Item, DeviceComponent, and each component type that your custom metric family monitors. This tag includes the following tags:
  • <DestCert>—The name of the related item to which the expression contributes.
  • <ExpressionList>—This tag contains the expressions that are defined for the attributes in the group. This tag includes the following tag:
    • <Expression>—Include at least one of these tags in each expression list. These tags define how to calculate the values for a given attribute. This tag includes the following tags:

      – <DestAttr>

      – <Expression>

Note: For more information about each XML tag, see the inline documentation provided in the MetricFamily.xsd and Component.xsd files. For code examples, see the ProcessInfoMFWithComponent.xml file. This example file defines a metric family for gathering process metrics.

More information:

Create a Custom Metric Family XML File

ExpressionGroupList

The following information describes performing calculations from elements in the attribute list. Often calculations are trivial assignments, such as the process ID.

Note: Do not confuse the metric family and vendor certification ExpressionGroups. The metric family exposes its attributes with a URI of the following form:

{http://im.ca.com/normalizer}Name.AttributeName

The attributes are referred to in the vendor certification ExpressionGroup.

The metric family ExpressionGroup populates the database with different items that are addressed using a DestCert and a DestAttr URI. The value is computed in the Expression, which typically are trivial assignments of elements in the attribute list.

For example, the following illustration shows how {http://im.ca.com/inventory}Process.ProcessID is mapped to the PID attribute from the metric family AttributeList.

The following DestCert URIs must exist: