Search plug-ins

6.2 Search plug-ins

The search-plugin is an object, which is informed about the current state of the search and may influence the behavior of the search. They are divided into search-plugins that change the search behavior and plugins used for collecting and sharing information. Table 6.1 lists the search-plugins available in JaCoP and their membership in a respective group.

Table 6.1: Search plug-ins available in JaCoP.


changing search	cannot change search
	(information sharing)

solution listener	exit listener
exit child listener	time-out listener
consistency listener	initialize listener

The search plug-ins are called during search when they reach a specific state, as specified below.

Solution listener plug-in is called by search when a solution is found
Exit child listener plug-in is called every time the search exits the search subtree (it has four different methods; two methods, which are called when the search has exited the left subtree and two methods for the right subtree).
Consistency listener plug-in is called after consistency method at the current search node.
Exit listener plug-in is called each time the search is about to exit (it can be used to collect relevant search information).
Time-out listener plug-in is called when the time-out occurs (if specified).
Initialize listener plug-in is called at the beginning of the search.

Changing search plug-ins can override the status of the search by returning true or false status. For example, exit child listener method leftChild can override the status of the search by returning true or false status. If it returns true then the search continues and enters the right child to keep looking for a solution. Returning false instructs the search to skip exploring the right subtree

JaCoP makes it possible to combine several plugins hierarchically. Each listener may have multiple children listeners attached to it, which have potential to influence the behaviour of the parent. A very simple example of using this behavior, is using one listener to remember solution and another one to print it. These two different functionalities may be provided by two different listeners. In general, if search calls several children listeners the parent listener decides how to treat the results returned by them. The listeners already implemented in JaCoP use the following default rule to combine the return codes from different listeners. They combine their own return code with the return code of a child listener using conjunction of return codes. Several child listeners combine their return codes using disjunction of return codes.

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