Designing Policy Based Management in Microsoft SQL Server 2008
When you define a WHERE clause for a data manipulation language (DML) statement, you set a condition for the DML statement that defines the set of rows that meet your specific inclusion criteria. Within the Policy Based Management framework, conditions are the equivalent of a WHERE clause that defines the criteria needing to be checked.
You define the conditions that you want to check or enforce for a policy by defining criteria for the properties of a facet. Just like a WHERE clause, a condition can be defined by one or more facet properties, and a single facet property can be checked for multiple criteria. The comparison operators that can be used are restricted by the data type of the property. For example, a property of type string can be checked with =, <>, LIKE, NOT LIKE, IN, or NOT IN, whereas a boolean type can only be checked for = and <>.
If a condition that you want to check for a facet does not have a specific property that can be used, you can use the advanced editor to define complex conditions that compare multiple properties and incorporate functions. For example, you can check that every table has a primary key and that a table with a single index must be clustered. Unfortunately, if you define a condition using the advanced editor, a policy that incorporates the condition must be executed manually and cannot be scheduled.
Conditions are checked in a single step. You cannot have a condition pull a list of objects, iterate across the list of objects, and then apply subsequent checks. To work within the Policy-Based Management framework, conditions need to return a True or False value. Therefore, when building complex conditions with the advanced editor, you cannot return a list of objects that do not meet your criteria. You have to define the condition such that if any object does not meet your criteria, a value of False is returned.
Although you can check many properties of a facet within a single condition, a single condition can’t be defined for multiple facets. For example, you can check all 10 of the properties for the Surface Area Configuration facet in a single condition, but you have to define a second condition to check a property of the Surface Area Configuration for Analysis Services.