This page (revision-59) was last changed on 13-Jun-2014 18:25 by Albrecht Striffler

This page was created on 26-Oct-2012 10:15 by Joachim Baumeister

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A condition can look like {{"temperature > 38"}} or {{"weather = rain"}}. Such simple conditions can be combined to more complex ones, using the following syntax:
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A condition can look like ''"temperature > 38"'' or ''"weather = rain'"'. Such simple conditions can be combined to more complex ones, using the following syntax:
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Actions might be {{"Show warning = Yes"}} or {{"umbrella = Yes"}}
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In a rule action we can set other questions or variables. Examples could be ''"Show warning = Yes"'' or ''"umbrella = Yes"''\\
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It is also possible to set more complex values and values depending on other variables. For more information, go to [Extended Expressions: Conditions and actions | Doc Expressions], but be aware, that this extension is non-LGPL-licensed for commercial use.
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{{{%%Rule
{{{
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%}}}
}}}
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!!Except Conditions
!!EXCEPT Conditions
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Furthermore it is possible to add an exception condition to the rule, like in the following example:
Furthermore, it is possible to add an exception condition to the rule, like in the following example:
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!!Combining Rules
!!ELSE Actions
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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.
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 (e.g. ''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.
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!!UNKNOWN Actions
In d3web/KnowWE, every question can, besides their normal values, also have the value ''Unknown''. This means, that the value of the question is currently actually unknown or unknowable (which is different from not answering the question).\\
If a rule uses a question which currently has the value ''Unknown'' will result in the rule not being evaluated and therefor the action will not fire.
__Example:__ Lets assume, the temperature is currently unknown, because the sensor is broken. In this case, we really do not know whether the roads are icy or not. So to expand on the example above, we can do the following:
{{{
IF temperature < 0
THEN icy roads = Yes
ELSE icy roads = No
UNKNOWN icy roads = No
}}}This way, if the ''temperature'' is ''Unknown'', we also set the variable/question ''icy roads'' to ''Unknown'', without having the write rules for each of the actions.
Be aware that, if you just use THEN and ELSE __without__ an action for UNKNOWN, the action of ELSE will also fire if ''temperature'' is ''Unknown''.
!!ELSE and UNKNOWN in combination with EXCEPT
It is also possible to use an EXCEPT condition together with ELSE and UNKNOWN. If the EXCEPT condition is true, the ELSE action will fire. The UNKNOWN action only fires if the original IF condition is ''Unknown''. For clarification, check out the following truth tables:
\\
__Rule with THEN and ELSE action only__:
|| IF Condition || EXCEPT Condition || THEN Action || ELSE Action
| %%(color:green)true%% | %%(color:green)true%% |   | %%(color:green)fire%%
| %%(color:red)false%% | %%(color:green)true%% |   | %%(color:green)fire%%
| %%(color:grey)unknown%% | %%(color:green)true%% |   | %%(color:green)fire%%
| %%(color:green)true%% | %%(color:red)false%% | %%(color:green)fire%% |  
| %%(color:red)false%% | %%(color:red)false%% |   | %%(color:green)fire%%
| %%(color:grey)unknown%% | %%(color:red)false%% |   | %%(color:green)fire%%
| %%(color:green)true%% | %%(color:grey)unknown%% | %%(color:green)fire%% |  
| %%(color:red)false%% | %%(color:grey)unknown%% |   | %%(color:green)fire%%
| %%(color:grey)unknown%% | %%(color:grey)unknown%% |   | %%(color:green)fire%%
__Rule with THEN and ELSE and UNKNOWN action__:
|| IF Condition || EXCEPT Condition || THEN Action || ELSE Action || UNKNOWN Action
| %%(color:green)true%% | %%(color:green)true%% |   | %%(color:green)fire%% |  
| %%(color:red)false%% | %%(color:green)true%% |   | %%(color:green)fire%% |  
| %%(color:grey)unknown%% | %%(color:green)true%% |   | %%(color:green)fire%% |  
| %%(color:green)true%% | %%(color:red)false%% | %%(color:green)fire%% |   |  
| %%(color:red)false%% | %%(color:red)false%% |   | %%(color:green)fire%% |  
| %%(color:grey)unknown%% | %%(color:red)false%% |   |   | %%(color:green)fire%%
| %%(color:green)true%% | %%(color:grey)unknown%% | %%(color:green)fire%% |   |  
| %%(color:red)false%% | %%(color:grey)unknown%% |   | %%(color:green)fire%% |  
| %%(color:grey)unknown%% | %%(color:grey)unknown%% |   |   | %%(color:green)fire%%
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This page (revision-59) was last changed on 13-Jun-2014 18:25 by Albrecht Striffler Top