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databasedatabase-designboolean-logicboolean-expression

Database model for saving random boolean expressions

I have expressions like this:

(cat OR cats OR kitten OR kitty) AND (dog OR dogs) NOT (pigeon OR firefly)

Anyone having idea how to make tables to save those?

Before I got request for usage of brackets, I limited usage of operators to avoid ambiguous situations. So only ANDs and NOTs or only ORs and saved those in this manner:

operators 

id | name  
1  | AND  
2  | OR  
3  | NOT

keywords

id | keyword  
1  | cat  
2  | dog  
3  | firefly

expressions 

id | operator | keywordId  
1  | 0        | 1   
1  | 1        | 2  
1  | 3        | 3

which was: cat AND dog NOT firefly

But now, I'm really puzzled...

Solution

  • I think you need a possibility to concat "subexpressions". Why not have a nullable foreignkey in Table Expressions linking to itself(to the parent expression)?