WHERE Clause

The WHERE clause is represented by QueryExp, an abstract class. The concrete subclasses are AndQueryExp, OrQueryExp, NotQueryExp, and BinaryRelQueryExp. Instances of these expressions are combined together in the form a parse tree that represents the original conditional expression.

The interior nodes of this tree consist of AndQueryExp, OrQueryExp, and NotQueryExp instances. These instances represent AND, OR, and NOT expressions, which in turn can consist of other AND, OR, and NOT expressions and binary relations.

The leaf nodes are BinaryRelQueryExp, which represent expressions of the form property operator constant. This represents a binary relation between a property and a constant value. You retrieve property operator constant using the getLeftValue, getRightValue, and getOperator methods.

Each QueryExp has an apply method, which when passed in a CIMInstance returns a boolean. The boolean is true if the conditional expression represented by the QueryExp is true for the CIMInstance. Otherwise, the boolean returns false.

The QueryExp has two other useful methods, canonizeDOC and canonizeCOD, which are used to simplify conditional expressions for further processing. The canonizeDOC method converts the parse tree from an arbitrary combination of ANDs and ORs to a canonical Disjunction of Conjunctions form (OR of ANDs). The canonizeCOD method converts the parse tree from an arbitrary combination of ANDs and ORs to canonical Conjunction of Disjunctions form (AND of ORs). These classes and methods are used by providers that need to filter instances based on input queries.

More details of these classes can be found in the Javadoc reference pages. See file:/usr/sadm/lib/wbem/doc/index.html.