5.8.5. Different types of nodes in a ruleflow
A ruleflow is a flow chart where different types of nodes are linked using connections. It has the following properties: a (unique) id, a (display) name and a version. You can also specify how the connections are visualized on the canvas using the connection layout property:
manual always draws your connections as lines going straight from their start to end point (with the possibility to use intermediate break points)
shortest path is similar, but it tries to go around any obstacles is might encounter between the start and end point (to avoid lines crossing nodes)
manhatten draws connections by only using horizontal and vertical lines
Figure 5.52. The different types of ruleflow nodes
Currently, ruleflow supports eight types of nodes:
Start: the start of the ruleflow. A ruleflow should have exactly one start node. The start node cannot have incoming cnnections and should have one outgoing connection. It contains one property "name" which is the display name of the node. Whenever ruleflow process is started, the ruleflow will start executing here and automatically continue to the first node linked to this start node
End: the end of the ruleflow. A ruleflow should have one or more end nodes. The end node should have one incoming connection and cannot have outgoing connections. It contains one property "name" which is the display name of the node. When an end node is reached in the ruleflow, the ruleflow is terminated (including other remaining active nodes when parallelism is used).
RuleFlowGroup: represents a set of rules. A RuleFlowGroup node should have one incoming connection and one outgoing connection. It contains a property "name" which is the display name of the node, and the property ruleflow-group which is used to specify the name of the ruleflow-group that represents the set of rules of this RuleFlowGroup node. When a RuleFlowGroup node is reached in the ruleflow, the engine will start executing rules that are part of the corresponding ruleflow-group. Execution will automatically continue to the next node if there are no more active rules in this ruleflow-group. This means that, during the execution of a ruleflow-group, it is possible that new activations belonging to the currently active ruleflow-group are added to the agenda due to changes made to the facts by the other rules. Note that the ruleflow will immediately continue with the next node if it encounters a ruleflow-group where there are no active rules at that point.
Split: allows you to create branches in your ruleflow. A split node should have one incoming connection and two or more outgoing connections. It contains a property "name" which is the display name of the node. There are three types of splits currently supported:
AND means that the control flow will continue in all outgoing connections simultaneously
XOR means that exactly one of the outgoing connections will be chosen. Connections are chosen by evaluating the constraints that are linked to each of the outgoing connections. Constraints are specified using the same syntax as the left-had side of a rule. The constraint with the lowest priority number that evaluates to true is selected. Note that you should make sure that at least one of the outgoing connections will evaluate to true at runtime, or the ruleflow will throw an exception at runtime if it cannot find an outgoing connection. For example, you could use a connection which is always true with a high priority number to specify what should happen if none of the other connections can be taken.
OR means that all outgoing connections whose condition evaluates to true are selected. Conditions are similar to the XOR split, except that the priorities are not taken into account. Note that you should make sure that at least one of the outgoing connections will evaluate to true at runtime, or the ruleflow will throw an exception at runtime if it cannot find an outgoing connection.
Join: allows you to synchronize multiple branches. A join node should have two or more incoming connections and one outgoing connection. It contains a property "name" which is the display name of the node. There are two types of splits currently supported:
AND means that is will wait until all incoming branches are completed before continuing
XOR means that it continues if one of its incoming branches has been completed
Milestone: represents a wait state. A milestone should have one incoming connection and one outgoing connection. It contains a property "name" which is the display name of the node, and the property "constraint" which specifies how long the ruleflow should wait in this state before continuing. For example, a milestone constraint in an order entry application might specify that the ruleflow should wait until (a fact in the working memory specifies that) no more errors are found in the given order. Constraints are specified using the same syntax as the left-had side of a rule. When a Milestone node is reached in the ruleflow, the engine will check the associated constraint. If the constraint evaluates to true directly, the flow will continue imediately. Otherwise, the flow will continue if the constraint is satisfied later on, for example when a facts in the working memory is inserted, updated or removed.
Subflow: represents the invocation of another ruleflow from withing this ruleflow. A subflow node should have one incoming connection and one outgoing connection. It contains a property "name" which is the display name of the node, and the property "processId" which specifies the id of the process that should be executed. When a Subflow node is reached in the ruleflow, the engine will start the process with the given id. The subflow node will only continue if that subflow process has terminated its execution. Note that the subflow process is started as an independent process, which means that the subflow process will not be terminated if this process reaches an end node.
Action: represents an action that should be executed in this ruleflow. An action node should have one incoming connection and one outgoing connection. It contains a property "name" which is the display name of the node, and the property "action" which specifies the action that should be executed. When an action node is reached in the ruleflow, it will execute the action and continue with the next node. An action should be specified as a piece of (valid) MVEL code.