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Rules#

At this page, one can find the documentation concerning rules.

Definition #

Rules can be defined as one means for creating derivation knowledge. Thereby, a basic syntax exists that can be slightly varied to create different types of rules. Those types substantially vary in their distinct rule actions and they are explained in more detail after the presentation of the basic syntax.

Syntax #

In this section we describe the way rules are defined in d3web KnowWE.

Basics #

Rules are defined by the Rule tag in KnowWE. The basic syntax is as follows:

%%Rule
IF (rule condition) 
THEN (rule action) 
%

For more information about the possible conditions, see Doc Conditions.

It is possible to define more than one action to be executed for a rule. Just add more THEN clauses.

%%Rule
IF (rule condition) 
THEN (rule action 1)
THEN (rule action 2)
THEN (rule action 3) 
%

Furthermore it is possible to add an exception condition to the rule, like in the following example:

IF (rule condition 1)  
THEN (rule action) 
EXCEPT (rule condition 2) 

Of course it is also possible to define the EXCEPT(...) statement as AND NOT within the IF clause. The difference is, that EXCEPT(...) doesn't need to be evaluated, i.e. the rule will also fire even if the EXCEPT clause is not fulfilled or unknown.

The following operators can be used to build more complex expressions from simple rule conditions:

• NOT(rule condition) --- true, if rc does not apply
• (rule condition 1) AND (rule condition 2) --- true, only if both condition 1 and condition 2 apply at the same time
• (rule condition 1) OR (rule condition 2) --- true, if at least one of condition 1 and condition 2 does apply

Combining Rules#

Using such rules, we often not only want something to happen if the condition is true (e.g. temperature <= 0), but also when the condition is false. We can of course always do this, by writing a second rule, using the negated condition of the first rule (temperature > 0). With d3web KnowWE, we provide the possibility, to just use the keyword ELSE, similar to how it is known and done in software engineering.

IF temperature < 0
THEN icy roads = Yes
ELSE icy roads = No

Using eval()#

eval(...) expressions can also be used as rule condition if more than one question or complex formulas shall be used. To see all available expressions and functions, see Doc Expressions and Doc Functions

IF eval(question A = question B)
THEN (rule action)

IF eval(question A = 2 * x + b)
THEN (rule action)

or if a complex action shall be conducted

IF questionA < 2
THEN questionB = eval(max(question C, question D))

eval(...) must not be used in combination with KNOWN/UNKOWN

 
IF question A = UNKNOWN
THEN question B = 2

Different rule types #

As previously mentioned, the different rule types vary in their rule actions, that is, the part of the rule following the THEN keyword. In the following the rule types available in KnowWE are listed and shortly explained. For a more detailed explanation and syntax examples please refer to the separate pages for each rule type.

Scoring Rules #

Scoring rules (diagnosis rules) are used to assign specific score points to a solution. See the page about scoring rules. for the syntax and an overview of the possible score points.

Abstraction Rules #

It is possible to assign values to a question via abstraction rules. That way, the program sets certain answer values depending on those answer values provided by the user for previous questions. See the page about abstraction rules for the syntax and further detail.

Indication Rules #

Indication rules basically initiate the presentation of certain, subsequent questions or questionnaires to the user depending on previously provided answers. For syntax and further detail see the page about indication rules.