Add control functions in actions to optimize rules execution using Microsoft Rules Composer (Preview)

Applies to: Azure Logic Apps (Standard)

This guide describes how to optimize rules execution by adding control functions to actions in your rules using the Microsoft Rules Composer. Control functions help your application or ruleset control the facts in the rules engine's working memory. These functions include the Assert, Clear, Halt, Retract, RetractByType, Reassert, and Update functions for the .NET object and TypedXmlDocument entities that you can use as facts. The existence of facts in working memory drives the conditions that the engine evaluates and the actions that execute.

Prerequisites

• Download and install the Microsoft Rules Composer.

• The XML file that contains the ruleset that you want to work on.

  To add facts, specify their values in the XML documents that you point at from the RuleSet Explorer window. Or, you can use a fact creator to supply your rules engine with an array that contains .NET objects as facts. For more information, see Build fact creators and retrievers.

Assert function

To add object instances to the rules engine's working memory, use the Assert function in the Microsoft Rules Composer. The engine processes each object instance according to the conditions and actions that are written against the instance's type using the match-conflict resolution-action phases.

The following table summarizes the Assert function behavior for the supported asserted entities and instance types, including the number of resulting instances created in the engine for each asserted entity and the type applied to each instance for identification.

Assert a .NET object

The rules engine natively supports basic .NET scalar types and objects for reference types. Asserted .NET object processing is the most straightforward of the processing types.

In the Microsoft Rules Composer, you can assert a .NET object from within a rule.

1. In the Microsoft Rules Composer, load the XML file that contains the rule store you want to work on.

2. In the RuleSet Explorer window, find and select the rule that you want.

3. In the THEN pane, under Actions, add the Assert built-in function as an action.

4. In the Facts Explorer window, select .NET Classes.

5. From the .NET Classes tab, drag the constructor method for the object that you want to the argument in the Assert action.

   The Microsoft Rules Composer translates the constructor method into a CreateObject call in the rule definition.

   Note

   Although the rules engine has a CreateObject function, the function doesn't appear as a separate function in the Microsoft Rules Composer.

Each object is asserted into working memory as a separate object instance, which means that each predicate that references the object's type, such as IF Object.Property = 1, analyzes the instance. The instance is also available to rule actions that reference the type, based on the results of the rule conditions.

For example, suppose you have the following rules:

Rule 1

IF A.Value = 1
THEN A.Status = "good"

Rule 2

IF B.Value = 1
THEN A.Status = "good"

In Rule 1, only the A instances with a value of 1 have their Status property updated. In Rule 2, however, if the condition evaluates to true, all A instances have their status updated. In fact, if there are multiple B instances exist, the A instances are updated each time the condition evaluates to true for a B instance.

Assert a TypedXmlDocument entity

In the Microsoft Rules Composer, you can assert a TypedXmlDocument entity from within a rule.

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Assert built-in function as an action.

3. In the Facts Explorer window, select XML Schemas.

4. From the XML Schemas tab, drag the node that you want to the argument in the Assert action.

XML documents are basically text, but the field values might be any type, which is based on the specified type when the rule was built. Fields are XPath expressions, so they might return a nodeset, which means that the first item in the set is used as the value.

When a TypedXmlDocument entity is asserted as a fact, the rules engine creates TypedXmlDocument child instances, based on the selectors defined in the rule. You can think of selectors as a way to isolate the nodes in an XML document, and fields as identifying specific items within the selector. The rules engine groups all the fields inside one selector as an object.

Selectors are also XPath expressions. In the Facts Explorer, when you select a node on the XML Schemas tab, the Microsoft Rules Composer automatically fills in the XPath Selector property for all nodes and the XPath Field property for any node that doesn't contain child nodes. Alternatively, you can enter your own XPath expressions for XPath Selector and XPath Field if necessary. If the selector matches multiple portions in the XML document, multiple objects of this type are asserted into or retracted from the rules engine's working memory.

You can use multiple selectors within the same document. That way, you can view different parts of the document, for example, suppose one section is the order and another section contains the shipping address. However, keep in mind that the created objects are defined by the XPath string that created them. If you use a different XPath expression, the result is a unique TypedXmlDocument entity, even if the expression resolves to the same node.

For example, suppose you have the following XML:

<root>
    <order customer="Joe">
        <item name="router" quantity="10" cost="550" />
        <item name="switch" quantity="3" cost="300" />
    </order>
    <order customer="Jane">
        <item name="switch" quantity="1" cost="300" />
        <item name="cable" quantity="23" cost="9.99" />
    </order>
</root>

If you use the selector /root/order, or //order, the following objects are added to the engine's working memory:

Object 1

<order customer="Joe">
    <item name="router" quantity="10" cost="550" />
    <item name="switch" quantity="3" cost="300" />
</order>

Object 2

<order customer="Jane">
    <item name="switch" quantity="1" cost="300" />
    <item name="cable" quantity="23" cost="9.99" />
</order>

Within each selector, XPaths refer to the individual fields. So, if you use the selector /root/order/item, //order/item, or //item, the following objects are added to the engine's working memory with two items for Joe and the two items for Jane:

<root>
    <order customer="Joe">
    </order>
    <order customer="Jane">
    </order>
</root>

Each object can access three fields: @name, @quantity, and @cost. You can refer to the parent fields because the object is a reference into the original document, for example, ../@customer.

Behind the scenes, the rules engine can convert a text field value to any one of the supported types through the XmlConvert function. You can specify this option by setting the type in the Microsoft Rules Composer. If a conversion isn't possible, the engine throws an exception. You can retrieve the bool and double types only as their respective type, either strings or objects.

Clear function

To reset the working memory and agenda for a rules engine instance, use the Clear function in the Microsoft Rules Composer. For more information about working memory and agenda, see Rules engine optimization.

Reset working memory and agenda for your rules engine

1. In the RuleSet Explorer window, find and select the rule where you want to clear the working memory and agenda for your rules engine.

2. In the THEN pane, under Actions, add the Clear built-in function as an action.

   The Clear function takes no arguments.

Halt function

To stop the current execution by the rules engine, use the Halt function in the Microsoft Rules Composer.

Stop ruleset execution

1. In the RuleSet Explorer window, find and select the rule where you want to stop ruleset execution.

2. In the THEN pane, under Actions, add the Halt built-in function as an action.

The Halt function takes a single Boolean argument. If you specify the value as true, the rules engine clears the agenda that contains the pending candidate rules.

The Ruleset.Execute method is a wrapper around the RuleEngine.Execute method, and uses code that's similar to the following code:

RuleEngine.Assert(facts);
RuleEngine.Execute();
RuleEngine.Retract(facts);

If you use the Ruleset.Execute method to execute a ruleset, the rules engine returns control to the Ruleset.Execute method when the Halt function executes. The Ruleset.Execute method retracts the facts and returns control to the caller. In this case, the halted ruleset execution can't resume.

However, if you directly use the RuleEngine.Execute method to execute the ruleset, you can resume the halted ruleset execution with the next pending rule firing by calling RuleEngine.Execute again, provided that you didn't retract any objects needed between the two calls.

The following sample code shows how to resume the halted ruleset execution:

// Assert facts into working memory of the rules engine instance.
RuleEngine.Assert(facts);

// Execute the ruleset.
RuleEngine.Execute();

// The ruleset invokes the Halt method when executing actions.
// Control returns here when the Halt function is called. 
// When engine halts, do the following tasks.

// Add your code here.

// Resume the halted rules engine execution.
RuleEngine.Execute();

// Retract or remove facts from working memory in the rules engine.
RuleEngine.Retract(facts);

Retract function

To remove objects from a ruleset and from the rules engine's working memory, use the Retract function in the Microsoft Rules Composer.

Retract a .NET object

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Retract built-in function as an action.

3. In the Facts Explorer window, select .NET Classes.

4. From the .NET Classes tab, drag the class that you want, not the assembly or method, into the argument for the Retract parameter.

   If you drag a method into the Retract function, the engine attempts to retract the object returned by the method.

Retracting a .NET object has the following impact:

• Actions on the agenda that use the objects are removed from the agenda.

  Note

  Other actions higher up on the agenda might already have executed before you use the Retract function.

• Rules that use the object in a predicate have their actions removed from the agenda, if any actions exist on the agenda.

• The engine no longer evaluates the object.

Retract a TypedXmlDocument entity or entities

You can retract the original TypedXmlDocument entity that was asserted into the rules engine, or you can retract one of the TypedXmlDocument child entities created from the parent XmlDocument entity.

Suppose you have the following example XML:

<order>
    <orderline customer="Joe" linenumber="001">
        <product name="router" quantity="10" cost="550" />
    </orderline>
    <orderline customer="Jane" linenumber="002">
        <product name="switch" quantity="1" cost="300" />
    </orderline>
</order>

You can either retract the TypedXmlDocument entity associated with an order object, or you can retract one or both of the TypedXmlDocument entities associated with the orderline object. All TypedXmlDocument entities are associated with the top-level TypedXmlDocument entity that was originally asserted, not with the TypedXmlDocument entity that appears above that top-level TypedXmlDocument node in the XML tree hierarchy.

For example, product is a TypedXmlDocument entity below the orderline object and is associated with the TypedXmlDocument entity for order, not the TypedXmlDocument entity for orderline. In most instances, this distinction isn't important. However, if you retract the order object, the orderline and product objects are also retracted. If you retract the orderline object, only that object is retracted, not the product object.

The engine only works with and tracks the object instances, which are TypedXmlDocument instances, that the engine created when the TypedXmlDocument entity was initially asserted. If you create additional nodes, such as sibling nodes for a node that was selected through a selector in the ruleset, these nodes aren't evaluated in rules unless TypedXmlDocument entities are created and asserted for them. If you assert these new, lower-level TypedXmlDocument instances, the engine evaluates the instances in the rules, but the top-level TypedXmlDocument entity doesn't have knowledge about them. When the top-level TypedXmlDocument is retracted, the new, the independently asserted TypedXmlDocument entities aren't automatically retracted. As a result, if new nodes are created, perform a Retract and Reassert on the full XmlDocument, which is the typical and most straightforward step to take.

The TypedXmlDocument class provides useful methods that you can call within a custom .NET member as part of an action. These methods include the capability to get the XmlNode associated with the TypedXmlDocument or the parent TypedXmlDocument.

Retract the top-level TypedXmlDocument entity

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Retract built-in function as an action.

3. In the Facts Explorer window, and select XML Schemas.

4. From the XML Schemas tab, drag the top-level node for the schema into the argument for the Retract function.

   This top node ends in the .xsd extension and represents the document root node, not the document element node. The node has a / selector that refers to the initial TypedXmlDocument. When you retract the parent TypedXmlDocument, all TypedXmlDocument child entities associated with the TypedXmlDocument are removed from working memory, including all the TypedXmlDocument entities created by calling the Assert function, based on selectors used in the ruleset.

Retract a child TypedXmlDocument entity

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Retract built-in function as an action.

3. In the Facts Explorer window, and select XML Schemas.

4. From the XML Schemas tab, drag the child node into the argument for the Retract function.

RetractByType function

To remove all objects with the specified type from the rules engine's working memory, use the RetractByType function in the Microsoft Rules Composer. This function differs from the Retract function, which removes only specific items with a certain type.

Retract all .NET objects with a specific type

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the RetractByType built-in function as an action.

3. In the Facts Explorer window, select .NET Classes.

4. From the .NET Classes tab, drag the class into the argument for the RetractByType function.

Retract all TypedXmlDocument entities with a specific type

The RetractByType removes all TypedXmlDocument entities with the same DocumentType.Selector.

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the RetractByType built-in function as an action.

3. In the Facts Explorer window, select XML Schemas.

4. From the XML Schemas tab, drag the appropriate node to the RetractByType function.

Consistent with the Retract function, if you use the RetractByType function on the document root node, not only does this action retract all TypedXmlDocument entities asserted with that DocumentType, but also all the child TypedXmlDocument entities, or XmlNode nodes in the tree hierarchy, associated with those parent TypedXmlDocument entities.

Reassert function

To call the Assert function on an object that already exists in the engine's working memory, use the Reassert function in the Microsoft Rules Composer. The behavior is equivalent to issuing a Retract command for the object, followed by an Assert command.

For example, if you use the Reassert function on a .NET object, the rules engine takes the following steps:

1. Retract the .NET object from working memory.

2. Remove any actions on the agenda for rules that use the object in a predicate or action.

3. Assert the .NET object back into working memory and evaluate as a newly asserted object.

4. Reevaluate any rules that use the object in a predicate and add those rules' actions to the agenda as appropriate.

5. Readd the actions to the agenda for any rules that previously evaluated to true and only use the object in their actions.

Reassert a .NET object

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Reassert built-in function as an action.

3. In the Facts Explorer window, select .NET Classes.

4. From the .NET Classes tab, drag the class into the argument for the Reassert function.

Reassert a TypedXmlDocument entity

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Reassert built-in function as an action.

3. In the Facts Explorer window, select XML Schemas.

4. From the XML Schemas tab, drag the entity node that you want to the argument in the Reassert function.

If you reassert a top-level TypedXmlDocument entity, the TypedXmlDocument child entities, which were created when the the top-level TypedXmlDocument entity was first asserted, can behave differently, depending on the state of each TypedXmlDocument child entity.

For example, if a new or existing child entity is "dirty", meaning that at least one field was changed in the ruleset using an action, then an Assert function or Reassert function is performed on that child. Any existing child that isn't dirty stays in working memory.

The following example shows a simplified scenario that describes the child entity behaviors when their parent entity is reasserted. Suppose you have the following TypedXmlDocument entities in working memory: Parent, Child1, Child2, and Child3.

• Parent is the top-level TypedXmlDocument entity.
• Each child contains a field named ExampleField where the value is set to 1, for example, Child1.ExampleField = 1`.

Suppose a rule action performs the following operations on the child entities:

• The ExampleField value for Child2 is updated from 1 to 0.
• User code deletes Child3.
• User code adds a new TypedXmlDocument child entity named NewChild to Parent.

The following example shows the new representation of objects in working memory:

Parent
Child1 // Where Child1.ExampleField = 1
Child2 // Where Child2.ExampleField = 0
NewChild

Now, suppose you reassert the Parent entity, which results in the following child entity behaviors:

• Child2 is reasserted because it's now dirty after its field was updated.
• Child3 is retracted from working memory.
• NewChild is asserted into working memory.
• Child1 stays unchanged in working memory because it wasn't updated before Parent was reasserted.

Update function

To reassert an object into the rules engine for reevaluation, based on the new data and state, use the Update function in the Microsoft Rules Composer. The object can have .NET class type or TypedXmlDocument type. You can also use the Update function to improve engine performance and prevent endless loop scenarios.

Update a .NET object

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Update built-in function as an action.

3. In the Facts Explorer window, select .NET Classes.

4. From the .NET Classes tab, drag the class into the argument for the Update function.

Typically, you use Assert to place a new object in the rules engine's working memory, and use Update to update an already existing object in working memory. When you assert a new object as a fact, the engine reevaluates the conditions in all the rules. However, when you update an existing object, the engine reevaluates only conditions that use the updated fact and adds actions to the agenda, if these conditions evaluate to true.

For example, suppose you have the following rules and that the objects named ItemA and ItemB already exist in working memory.

• Rule 1 evaluates the Id property in ItemA, sets the Id property on ItemB, and then reasserts ItemB after the change. When ItemB is reasserted, the engine treats ItemB as a new object, and the engine reevaluates all rules that use ItemB in the predicates or actions. This behavior makes sure that the engine reevaluates Rule 2 against the new value in ItemB.Id as set in Rule 1.

  Rule 1

  IF ItemA.Id == 1
  THEN ItemB.Id = 2
  Assert(ItemB)
  

• Rule 2 might fail the first evaluation, but evaluates to true during the second evaluation.

  Rule 2

  IF ItemB.Id == 2
  THEN ItemB.Value = 100
  

The capability to reassert objects into working memory gives you explicit control over the behavior in forward-chaining scenarios. However, this example reveals a side effect from reassertion where Rule 1 is also reevaluated. With ItemA.Id unchanged, Rule 1 again evaluates to true, and the Assert(ItemB) action fires again. As a result, the rule creates an endless loop situation.

Prevent endless loops

You must be able to reassert objects without creating endless loops. To avoid such scenarios, you can use the Update function. Like the Reassert function, the Update function performs the Retract and Assert functions on the associated object instances that are changed by rule actions, but with the following key differences:

• On the agenda, actions for rules stay on the agenda when the instance type is only used in the actions, not the predicates.

• Rules that only use the instance type in actions aren't reevaluated.

As a result, rules that use the instance types, either in only the predicates or both the predicates and actions, are reevaluated, and the rules' actions are added to the agenda as appropriate.

By changing the preceding example to use the Update function, you can make sure that the engine reevaluates only Rule 2 because the condition for Rule 2 uses ItemB. The engine doesn't reevaluate Rule 1 because ItemB is only used in the actions for Rule 1*, eliminating the looping scenario.

Rule 1

IF ItemA.Id == 1
THEN ItemB.Id = 2
Update(ItemB)

Rule 2

IF ItemB.Id == 2
THEN ItemB.Value = 100

Despite using the Update function this way, the possibility still exists for creating looping scenarios. For example, consider the following rule:

IF ItemA.Id == 1
THEN ItemA.Value = 20
Update(ItemA)

The predicate uses ItemA, so the engine reevaluates the rule when Update is called on ItemA. If the value for ItemA.Id isn't changed elsewhere, Rule 1 continues to evaluate as true, which causes calling Update again on ItemA.

As the rule designer, you must make sure to avoid creating such looping scenarios. The appropriate approach to fix this problem differs based on the nature of the rules.

The following example shows a simple way to solve the problem in the preceding example by adding a check on ItemA.Value that prevents the rule from evaluating as true again after the rule's actions executed the first time.

IF ItemA.Id == 1 and ItemA.Value != 20
THEN ItemA.Value = 20
Update(ItemA)

Update a TypedXmlDocument entity

1. In the RuleSet Explorer window, find and select the rule that you want.

2. In the THEN pane, under Actions, add the Update built-in function as an action.

3. In the Facts Explorer window, select XML Schemas.

4. From the XML Schemas tab, drag the entity node that you want to the argument in the Update function.

For example, suppose you have the following rules:

• Rule 1 evaluates the total count of the items in a purchase order message.

  IF 1 == 1
  THEN ProcessPO.Order:/Order/Items/TotalCount = (ProcessPO.Order:/Order/Items/TotalCount + ProcessPO:/Order/Items/Item/Count)  
  

• Rule 2 sets the status to "Needs approval" if the total count is greater than or equal to 10.

  Rule 2

  IF ProcessPO.Order:/Order/Items/TotalCount >= 10
  THEN ProcessPO.Order:/Order/Status = "Needs approval"
  

If you pass the following purchase order message as input to this ruleset, you notice that the status isn't set to "Needs approval", even though the TotalCount is 14. This behavior happens because Rule 2 is evaluated only at the start when the TotalCount value is 0. The rule isn't evaluated each time when TotalCount is updated.

<ns0:Order xmlns:ns0="http://ProcessPO.Order">
    <Items>
        <Item>
            <Id>ITM1</Id>
            <Count>2</Count>
        </Item>
        <Item>
            <Id>ITM2</Id>
            <Count>5</Count>
        </Item>
        <Item>
            <Id>ITM3</Id>
            <Count>7</Count>
        </Item>
        <TotalCount>0</TotalCount>
    </Items>
    <Status>No approval needed</Status>
</ns0:Order>

To have the engine reevaluate the conditions each time when TotalCount is updated, you have to call the Update function on the parent node (Items) for the updated node (TotalCount). If you change Rule 1 as follows, and test the rule one more time, the Status field is set to "Needs approval":

Rule 1 (updated)

IF 1 == 1
THEN ProcessPO.Order:/Order/Items/TotalCount = (ProcessPO.Order:/Order/Items/TotalCount + ProcessPO:/Order/Items/Item/Count) AND
Update(ProcessPO.Order:/Order/Items)

Related content

• Create rules with the Microsoft Rules Composer
• Add arithmetic and logical operators to rules
• Test your rulesets
• Create an Azure Logic Apps Rules Engine project