Your company has a private cloud that is managed by using a System Center 2012 Operations
Manager infrastructure.
The network contains an Active Directory forest named adatum.com.
Operations Manager monitors a server named Operations1.
Operations1 has a computer account in an organizational unit (OU) name ServerOU1.
You create a group named GP1 as shown in the exhibit. (Click the Exhibit button.)

You create a rule named OMRule1 that generates an alert when an error is added to the Application
log.
You target OMRule1 to GP1.
You discover that alerts fail to be generated when errors are added to the Application log on
Operations1.
You need to ensure that an alert is generated when an error is added to the Application log on
Operations1.
What should you modify?

A.
the target of OMRulel1

B.
the dynamic membership of GP1

C.
the category of OMRule1

D.
the explicit membership of GP1

Explanation:
How does a rule get to an agent?
For any particular rule/monitor, OpsMgr will enumerate all instances of the target class and apply
the rule to each.
If there are no instances of the target class on a particular agent, then the rule will do nothing.
It’s that simple.
If I can’t target groups, why are they listed when I select a target for a rule? Groups are classes just
like any other.
They’re singleton classes where the class and the instance are one and the same, but they are
classes nonetheless which is why they show up in the list with all other classes.

There are really very few circumstances where you will target a rule at a group though.
What if I do target a group?
You can apply a rule/monitor directly to a group, but it will execute against the group object itself.
OpsMgr will not enumerate members of the group and apply the rule to each.
Any rules targeted at groups will actually operate on the Root Management Server since groups have
no host and unhosted objects are managed by the RMS.
How do I target some group of objects then?
To the specific question of how to get a particular rule/monitor to a subset of components, you have
two basic options.
Let’s say for example, you have a particular subset of web sites that you need a particular rule to
apply.
You could target that rule at the IIS 2003 Web Site class for example, but that would apply the rule
to all instances of that class.
It would probably apply to sites that you didn’t want.
Option 1 would be to create a new class and target the rule at the class.
In the case of an IIS site, this would mean that you would need to go to the Authoring Console or raw
XML and create a new class and discovery.
That’s a more advanced solution that most customers will do and probably overkill anyway.
Option 2 is the create a rule target at the whole class and disable it.
Create a group with the sites you want and create an override for that group to enable your rule.
This might sound like a workaround, but it’s a completely valid solution.
How do I know if I’m selecting the right target?
The easiest method to validate you are using a target that actually has instances is to use the
Discovered
Inventory view in the Operations Console prior to creating your rule/monitor.
In the Actions pane is an option called “Change target type…” that will bring up the same Select a
Target Type dialog box that you see when you select the target for a rule/monitor.
This view will list all instances of the target class you select.
You can validate which agents have an instance of that class and how many instances each has.
If there are no instances listed, then the rule isn’t going to do anything.
If there are instances, then you not only be confident that the rule/monitor will execute on the
agent, but you can also view the properties of the instance that will be accessible to any
rules/monitors targeted at it.
http://blogs.technet.com/b/brianwren/archive/2007/08/22/targeting-rules-and-monitors.aspx
NOTE:
The text below was copied from a duplicate question
https://social.technet.microsoft.com/wiki/contents/articles/7205.operations-managerdynamicgroup-examples.aspx
Operations Manager Dynamic Group Examples
In Operations Manager, groups are logical collections of objects, such as Windows-based computers,
hard disks, or instances of Microsoft SQL Server.
Groups are populated by explicitly adding objects to the group or dynamically according to criteria
you set.
For more information on the use of groups, see Creating and Managing Groups in the Operations
Guide.
This article provides example of group definitions.
The examples describe the items to select in the Query Builder and the resulting formula: