5.%20Aggregation%20and%20Negation - PowerPoint PPT Presentation
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5.%20Aggregation%20and%20Negation
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1. 5. Aggregation and Negation. 5.1 Set grouping. R0(y1,...,ym) : R(x1,...xn) where each yi is either xj or xj . is similar to GROUP BY in SQL. Example: ... – PowerPoint PPT presentation
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Title: 5.%20Aggregation%20and%20Negation
1
5. Aggregation and Negation
- 5.1 Set grouping
- R0(y1,,ym) R(x1,xn)
- where each yi is either xj or ltxjgt.
- lt gt is similar to GROUP BY in SQL.
- Example
- Reach(x, ltygt) Can_Send_Message(x, y).
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- 5.2 Average, Count, Sum
- These require the aggregated attribute(s) to be
- constants in each constraint tuple.
- Example
- Reach(x, countltygt) Can_Send_Message(x, y).
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- 5.3 Area and Volume
- Example
- Town_Area(t, arealtx,ygt) Town(t, x, y).
- 5.4 Minimum and Maximum
- Aggregation argument a linear function
- Example
- Profit(maxlt30x125x28x315x4gt) Crops(x1, x2,
x3, x4).
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- 5.5 Negation
- R0(x1,,xk) not R(x1,,xk).
- Example
- Not_Covered(x, y) not Covered(x, y).
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- 5.6 Stratified Datalog Queries
- A query is evaluated and its output (semantics)
- will be an input to another query.
- Example
- Faster(x, y, minlttgt) Travel(x, y, t).
- Travel is the output of a query Qtravel. Now it
is also - the input to the above query Qfastest.
- The entire query is written Qfastest(Qtravel()).
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