Type of comparison
After the initial loading and setup of the CIs is complete, the next step is to identify the CIs to be compared. The comparison service performs two types of comparisons: compare regular and compare recursive. These comparisons are further enhanced by specifying the cardinality for the compare: one-to-one and many-to-one.
The following table describes the different types of comparison:
Types of comparison | Description |
|---|---|
Compare Regular | A Compare Regular refers to the comparison of top level CIs only. No other related CIs are compared. |
Compare Recursive | A Compare Recursive compares the top level CIs and their children with a weak relationship. The qualification set that you apply to your baseline or target only selects the top-level CIs. The comparison service loads all the weak relationship children for a CI and compares them as well. All child CIs, at all levels, are loaded. |
One-to-One | The comparison service must identify which two CIs in the baseline and the target represent the same instance. |
Many-to-One | A many-to-one comparison is used when you want to check a pre-defined configuration, the golden server, against all CIs of the same kind. With a many-to-one comparison, you compare many target CIs with one baseline CI. Each CI in the target is compared with the single CI in the baseline. The number of CIs in the baseline cannot be more than one. If the qualification set you apply to the baseline evaluates more than one CI, the comparison service stops execution and displays the following error message: Many to one specified: Baseline must have a single CI. This baseline has _<NN>_ CIs. |
There are no restrictions on the number of CIs in the target.
If the Compare Recursive option is selected when creating a comparison job, the same logic cannot be used to identify the child CIs. To correctly identify the child CIs, the comparison service uses the Reconciliation Identification Rules located in the RE:Identify_Rules form. These rules specify the attributes per class that need to match to be identified. For example, the Reconciliation Engine rule states that for Product CIs the Class type, Name, and Version number must match.
Additionally, the difficulty with a many-to-one comparison is identifying the CIs instances. The ReconciliationIdentity attribute cannot be used in a many-to-one comparison because the same CI instances are not being compared. Instead, the top-level CI is identified by class type. For example, if the baseline CI belongs to the BMC_ComputerSystem class, then all CIs in the target are compared for that class. All others are ignored.