Hi Nil, 

Is there a way to get the value from a NumberNode?  In other words, can I 
get the 4 out of (NumberNode 4)?  I need to do some other, quite general 
intermediate calculations and then produce another NumberNode; how do I 
best do that?

Johannes

>
> There are different ways to do that, and they depend on what you 
> intend to do with the knowledge. One way would be to use value 
>
> https://wiki.opencog.org/w/Value 
>
> for instance to attach a score of 3 to John, you'd say 
>
> ``` 
> (define john (Concept "John")) 
> (define score (Concept "score")) 
> (cog-set-value! john score (Number 3)) 
> ``` 
>
> then you may ask John's score with 
> ``` 
> (cog-value john score) 
> ``` 
> which will return 3. 
>
> Later on you may update John's score with 
> ``` 
> (cog-set-value! john score (Number 4)) 
> ``` 
>
> And 
> ``` 
> (cog-value john score) 
> ``` 
> which will return 4. 
>
> The problem with that (and with mutability in general) is that you 
> lose information. So for instance you won't be able to use reasoning 
> or specialized forms thereof like pattern mining to analyze the 
> evolution of your data. For that you need to keep track of these 
> updates. One way could be to use AtTimeLink, so for instance you way 
> write that at 10pm John had a score of 3 
>
> AtTimeLink 
>    Evaluation 
>      Predicate "score-of" 
>      List 
>        (Concept "John") 
>        (Number 3) 
>    TimeNode "10pm" 
>
> but at 11pm he had a score of 4 
>
> AtTimeLink 
>    Evaluation 
>      Predicate "score-of" 
>      List 
>        (Concept "John") 
>        (Number 4) 
>    TimeNode "10pm" 
>
> Etc... There are many ways to represent knowledge. 
>

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