Appendix: how the ENVS and QRES stacks work ( M0 example)

K.Subieta. SBA and SBQL, appendix, slide 1 Sept. 2006

Appendix: how the ENVS and QRES stacks work (M0 example)

Presentation prepared for OMG Object Database Technology Working Group

OMG TECHNICAL MEETING, Anaheim, CA USASeptember 25-29, 2006

by

Prof. Kazimierz Subieta

Polish-Japanese Institute of Information Technology, Warsaw, Poland [email protected]://www.ipipan.waw.pl/~subietaSBA/SBQL pages: http://www.sbql.pl


Query addressing a tiny database

• Query: For each department get its reference and the average sal of its employees.

• SBQL: Dept join avg((employs.Emp).sal)

• Tiny database:

• Expected result: bag{ struct{i17, 2500}, struct{i22, 1450} }


Query syntax tree and execution scenarioDept join avg( ( employs . Emp ) . sal )

join

Dept avg

.

. sal

employs Emp

2nd dot

1st dot

join 1st dot 2nd dot avg

1st Dept

2nd Dept

1st employs

2nd employs

1st Emp

2nd Emp

3rd Emp3rd employs


0Dept join avg( ( employs . Emp ) . sal )

Emp(i1) Emp(i5) Emp(i9) Dept(i17) Dept(i22)

ENVS QRES

empty

Start




ENVS QRES

bag{ i17 , i22 }

After binding Dept




ENVS QRES

bag{ i17 , i22 }

join starts 1st loop of the iteration over top of QRES

dname(i18) loc(i19) loc(i20) employs(i21)

nested




ENVS QRES

bag{ i17 , i22 }


After binding employs

i21




ENVS QRES

bag{ i17 , i22 }


i21

dot starts iteration on top of QRES

Emp(i1)nested




ENVS QRES

bag{ i17 , i22 }


i21

Emp(i1)

After binding Emp

i1




ENVS QRES

bag{ i17 , i22 }


Closing the iteration by the first dot

i1




ENVS QRES

bag{ i17 , i22 }


i1

Second dot starts iteration over top of QRES

name(i2) sal(i3) worksIn(i4)

nested




ENVS QRES

bag{ i17 , i22 }


i1


After binding sal

i3




ENVS QRES

bag{ i17 , i22 }


i3

Closing the iteration by the second dot




ENVS QRES

bag{ i17 , i22 }


2500

After performing avg on top of QRES




ENVS QRES

bag{ i17 , i22 }


2500

join forms the first partial result

struct{ i17, 2500 }Partial result of join:


After ending the 1st loop by join



ENVS QRES

bag{ i17 , i22 }





ENVS QRES

bag{ i17 , i22 }

join starts 2nd loop of the iteration over top of QRES

dname(i23) loc(i24) employs(i25) employs(i26)

nested



After binding employs



ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }





ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }

First dot starts 1st loop of iteration on top of QRES

nestedEmp(i5)



After binding Emp



ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }

Emp(i5)


i5


Forming 1st partial result of the first dot



ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }


i5Partial result of dot:




ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }



First dot starts 2nd loop of iteration on top of QRES

nestedEmp(i9)




ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }



Emp(i9)

After binding Emp

i9




ENVS QRES

bag{ i17 , i22 }


bag{ i25 , i26 }


i5Partial results of dot: i9

Forming 2nd partial result of the first dot




ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }


Closing iteration by the first dot, forming its result




ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }


Second dot starts 1st loop of iteration on top of QRES

nested





ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }



After binding sal

i7




ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }


Forming 1st partial result of the second dot





ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }



Second dot starts 2nd loop of iteration on top of QRES

nested

name(i10) sal(i11) address(i12) worksIn(i16)




ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }



name(i10) sal(i11) address(i12) worksIn(i16)

After binding sal

i11




ENVS QRES

bag{ i17 , i22 }


bag{ i5 , i9 }


i7Partial result of dot: i11

Forming 2nd partial result of the second dot




ENVS QRES

bag{ i17 , i22 }


bag{ i7 , i11 }


Closing iteration by the second dot, forming its result




ENVS QRES

bag{ i17 , i22 }


1450


After performing avg on top of QRES




ENVS QRES

bag{ i17 , i22 }


1450

struct{ i17, 2500 }Partial results of join:

join forms 2nd partial result

struct{ i22, 1450 }




ENVS QRES

bag{ struct{ i17, 2500}, struct{ i22 , 1450} }

Closing the iteration by join, forming the final result


In closing …

• Please note that this evaluation scenario concerns the formal semantics executed by the abstract machine.– Our goal is clear, universal and free of ambiguities semantic

specification rather than performance.

• In real implementation there are many obvious optimizations.

• The evaluation process is also the subject of many sophisticated optimizations (rewriting, indices, caching,…) .

• The entire process is executed in the main memory, hence the computations are not critical.– Critical computations concern the access to external storage and

network, and avoiding unnecessary (redundant) computations.

– This is the subject of major SBA optimization methods.

Documents

Appendix: how the ENVS and QRES stacks work ( M0 example)