| Prev | Next | Start of Chapter | Next Chapter | Contents | Glossary | Index | Comments | (10 out of 10)

The Rule Class

Rules have the following class-specific attributes:

Attribute	Description
`Options`	Declares whether the rule can be invoked using chaining, and also declares whether the rule can invoke other rules by using chaining. For any rule except a `when` or `whenever` rule, edit this attribute to declare participation in chaining to or from this rule.
Allowable values:	`invocable via forward chaining not invocable via forward chaining` `invocable via backward chaining not invocable via backward chaining` `may cause data seeking may not cause data seeking` `may cause forward chaining may not cause forward chaining`
Default value:	`if` rules, `initially` rules, and `unconditionally` rules: `invocable via forward chaining` `invocable via backward chaining` `may cause data seeking` `may cause forward chaining` `when` rules and `whenever` rules: `not invocable via forward chaining` `not invocable via backward chaining` `may cause data seeking` `may cause forward chaining`
Notes:	See Backward Chaining and Forward Chaining. By setting this attribute to `not invocable via forward chaining` and `not invocable via backward chaining`, you can make an `if` rule behave like a `when` rule.

`Tracing-and-breakpoints`	Declares the message levels for warning messages and tracing messages, and declares the breakpoint level. These settings pertain only to this rule. Use warning messages, tracing messages, and breakpoints when debugging your KB.
Allowable values:	`default`or, optionally, one of the following warning message levels: `warning message level 0 ( no warning messages ) warning message level 1 ( kb errors only ) warning message level 2 ( kb errors and deficiencies ) warning message level 3 ( kb errors, deficiencies, and other conditions )` and, optionally, one of the following tracing message levels: `tracing message level 0 ( no trace messages ) tracing message level 1 ( trace messages on entry and exit ) tracing message level 2 ( trace messages at major steps ) tracing message level 3 ( trace messages at every step )` and, optionally, one of the following breakpoint levels: `breakpoint level 0 ( no breakpoints ) breakpoint level 1 ( breakpoints on entry and exit ) breakpoint level 2 ( breakpoints at major steps ) breakpoint level 3 ( breakpoints at every step )`
Default value:	`default`
Notes:	See Chapter 42, Debugging and Tracing. A value of `default` in this attribute directs G2 to use the settings in the `Warning-message-level` attribute, `Tracing-message-level` attribute, and `Breakpoint-level` attribute of the Debugging Parameters system table. The `Tracing-and-breakpoints-enabled?` attribute of the Debugging Parameters system table must have the value `yes` for G2 to produce tracing messages and to recognize breakpoints.

`Scan-interval`	Specifies how often G2 should invoke this rule. G2 ignores this attribute for `initially` rules and `whenever` rules.
Allowable values:	`none`Any time interval
Default value:	`none`
Notes:	See Scanning Rules. If a generic rule has a scan interval, G2 invokes each generic rule invocation at the beginning of each scan interval.

`Focal-classes`	Associates the rule with one or more classes of objects. By executing a `focus` action that names a class of objects, your KB can invoke all rules whose `Focal-classes` attribute names that class.
Allowable values:	`none object`Name of any subclass of `OBJECT`
Default value:	`none`
Notes:	See Focusing on Rules and Invoking Rules by Category.

`Focal-objects`	Associates the rule with one or more named objects. By executing a `focus` action that names an object, your KB can invoke all rules whose `Focal-objects` attribute names that object.
Allowable values:	`none`Name of any object
Default value:	`none`
Notes:	See Focusing on Rules and Invoking Rules by Category.

`Categories`	Names one or more rule categories that pertain to this rule. When executing an `invoke` action that names a rule category as its only argument, G2 invokes all rules whose `Categories` attribute names that category. When executing an `invoke` action that names both a rule category and an object or an object class, G2 invokes all rules whose `Categories` attribute names that category and whose `Focal-objects` attribute name that object or whose `Focal-classes` attribute names that class.
Allowable values:	`none`Any non-reserved symbol
Default value:	`none`
Notes:	A rule category exists only if named in at least one enabled rule. See Focusing on Rules and Invoking Rules by Category.

`Rule-priority`	Specifies the priority for the rule invocation that G2 creates when this rule is invoked.
Allowable values:	Literal integer, from 1 (highest priority) to 10 (lowest priority)
Default value:	6
Notes:	See Prioritizing Rules. A rule's priority does not control the ordering of G2 scheduler tasks. Priorities propagate from rule to rule due to backward chaining. Priorities do not propagate due to forward chaining, or due to invoking a rule by executing a `focus` or `invoke` action.

`Depth-first-backward-chaining-precedence`	Specifies the precedence among a group of rules that G2 identifies for execution by using depth-first backward chaining. This attribute does not affect breadth-first backward chaining.
Allowable values:	Literal integer, 1 or greater
Default value:	1 (highest priority)
Notes:	By default, depth-first backward chaining causes G2 to invoke rules with lower precedence after rules with higher precedence have completed. Precedence differs from rule priority. For more information, see Using Depth-First Backward Chaining.

`Timeout-for-rule-completion`	Determines how long G2 attempts to invoke and execute a rule invocation before performing time-out processing.
Allowable values:	`none`(the rule never times out) `use default` (use the value in the `Timeout-for-inference-completion` attribute of the Inference Engine Parameters system table) Any time interval
Default value:	use default

Actions that Manipulate Rules

focus on {object | object-class}

Invokes all rules that are associated with the specified object or object class.

invoke rule-category-name [ { , | or } rule-category-name ] ... rules 
	for { object | object-class }

Invokes all rules that are associated with the specified rule category.

Expressions that Refer to Rules

One expression refers directly to rules.

To refer directly to a rule:

this rule 
->	rule

This expression produces the invoked rule within which this expression is evaluated. This expression is valid only in a rule. For example:

if the status of any custom-object O upon the workspace of this rule 
is not ok 
	then inform the operator that 
	  "An error has occurred; press the DIAGNOSIS button."

This whenever rule detects events that are associated with objects on its own workspace.

| Prev | Next | Start of Chapter | Next Chapter | Contents | Glossary | Index | Comments | (10 out of 10)

The Rule Class

Actions that Manipulate Rules

Expressions that Refer to Rules

| Prev | Next | Start of Chapter | Next Chapter | Contents | Glossary | Index | Comments | (10 out of 10)

Copyright © 1997 Gensym Corporation, Inc.