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Web Service Query Service

Manivasakan Sabesan and Tore Risch

Uppsala DataBase Laboratory

Dept. of Information Technology

Uppsala University

Sweden

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Outline

WSMED

Research Area

Adaptive Query Parallelization

Conclusion & Future work

• WSMED provides general query capabilities over data providing web services.

• Users only need to provide WSDL URLs of web services.

• WSMED automatically creates SQL views for each web service operation.

• It makes every web service operation query-able without any programming.

• Users can make any SQL query by using the automatically created SQL views.

WSMED (Web Service MEDiator) System

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Service Oriented Architecture of WSMED

WSMED Server

SQL View1

WSDL metadata 1

WS Operation 1

WS Operation p

WS Operation 1

WS Operation q

WS1 WSn

WSDL metadata n

Import metadata

SQL Viewm

IMPORTWSDL AUTHENTICATION QUERY EXIT_SINIT

WSMED Web Service Interface

TABLEINFO

SOAP call

WSMED Demo

• WSMED provides web service query service.

• WSMED Demo can be accessible from a web browser.

• Java Script is used to invoke directly WSMED web service.

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Outline

WSMED

Research Area

Adaptive Query Parallelization

Conclusion & Future work

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Queries calling data providing web services have a similar pattern :- dependent calls.

Web service calls incur high-latency and high message setup cost

A naïve implementation of an application making these calls sequentially is time consuming

A challenge here is to develop methods to speed up such queries with dependent web service calls

Research Problems

WS1 WS2 WS3 WSn

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Outline

WSMED

Research Area

Adaptive Query Parallelization

Conclusion & Future work

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Example Query

select gl.City , gl.TypeIdfrom GetAllStates gs, GetPlacesWithin gp, GetPlaceList glwhere gs.state=gp.state and gp.distance=15.0 and gp.placeTypeToFind='City' and gp.place='Atlanta' and gl.placeName=gp.ToPlace+' ,'+gp.ToState and gl.MaxItems=100 and gl.imagePresence='true'

Finds information about places located within 15 km from each City named ’Atlanta‘ in all US states.

• Invokes 300 web service calls and returns a stream of 360 tuples

<City,

TypeId>GetAllStates GetPlacesWithin GetPlaceList<state> <ToPlace,

ToState>

<15,’City’,’Atlanta’> <100,’true’>

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Query Processing in WSMED

Parallel query plan

SQL queryCalculus

Generator

Parallel pipeliner

Plan function generator

Non-parallel plan optimizer

Plan splitter

Phase 1

Phase 2

Non-parallel plan

γGetPlacesWithin(‘Atlanta’, state, 15.0, ‘City’)

<City, TypeId>

γGetPlaceList (str, 100, ‘true’)

γGetAllStates()

<state >

<city , state2 >

γconcat(city,’, ‘, state2)

<str>

Split point 1

Split point 2

PF1

PF2

Non-Parallel Plan

<str>

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Adaptive Parallel Plan

<state>

AFF_APPLYP(PF2, str)

<City, TypeId>

γGetAllStates()

AFF_ APPLYP(PF1, state)

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Parallel Process Tree

qi- query process (i=0,1,......n)PFj- Plan Function (j=1,......m)

Level 2

q0

q1

q3 q4

q2

GetAllStates

q5 q8q7q6

Coordinator

Level 1

Query

PF1

GetPlaceList

GetPlacesWithin

PF2

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AFF_APPLYP(Function PF, Stream pstream) → Stream result• PF – plan function

• pstream – stream of parameter values pi

• result – stream of results ri

• Asynchronous operator

q3

q4q5

PFPF

PFp1

p2

p3

Adaptive First Finished Apply in Parallel (AFF_APPLYP)

AFF_APPLYP

r1r2

r3

p4

p5

p6

PFp1, p2, p3

r1

p4

r3

p5

r2

p6

Functionalities of AFF_APPLYP

1. AFF_APPLYP initially forms a binary process tree by always setting fanout to 2 - init stage.

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q0

q1

q3 q4

q2

q6q5

Coordinator

Level 1

Level 2

..........2. A monitoring cycle for a non-leaf query process is defined when number of received end-of-call messages equal to number of children.

2.1 After the first monitoring cycle AFF_APPLYP adds p new child processes - an add stage.

3. When an added node has several levels of children, the init stages of AFF_APPLYP s in the children will produce a binary sub–tree.

q0

q1

q3 q4

q2

q5

Coordinator

Level 1 q7

q9q8q10Level 2 q6 q11

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......

4. AFF_APPLYP records per monitoring cycle i the average time ti to produce an incoming tuple from the children.

4.1 If ti decreases more than a threshold (25%) the add stage is rerun.

4.2 If ti increases we either add no more children or run a drop stage that drops one child and its children.

q0

q1

q3 q4

q2

q5

Coordinator

Level 1

q12q10Level 2 q6 q11

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Adaptive Results- Example Query

0

50

100

150

200

250

300

Execu

tio

n T

ime (

Sec)

Non-parallel plan p=1, no drop stage, fo1=3 fo2=3

p=1, drop stage, fo1=2 fo2=3 p=2, no drop stage, fo1=4 fo2=5

p=2, drop stage, fo1=3 fo2=3 p=3, no drop stage, fo1=5 fo2=3.4

p=3, drop stage, fo1=4 fo2=3.25 p=4, no drop stage, fo1=6 fo2=8.7

p=4, drop stage, fo1=5 fo2=4.2 p=5, no drop stage, fo1=7 fo2=7.5

p=5, drop stage, fo1=6 fo2=7.8

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AFF_APPLYP observations

• For example query :– The execution time with p=4 and no drop stage is the best. – It is more than 4 times faster with the sequential execution (non-

parallel).

• The execution time with p=2 and no drop stage is reasonably close to the best execution time ( 80% ).

• Drop stage makes insignificant changes in the execution

time.

• Fanout of each level on a process tree depends on the execution time of a web service invoked on that level. – AFF_APPLYP finds the optimized fanout for each level.

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Outline

WSMED

Research Area

Adaptive Query Parallelization

Conclusion & Future work

Related work

• Similar to WSMS (U.Srivastava, J.Widom, K.Munagala, and R.Motwani, Query

Optimization over Web Services, VLDB 2006) WSMED also invoke parallel web service calls. In contrast, WSMED supports automated adaptive parallelization.

• In contrast to WSQ/DSQ(R.Goldman, and J.Widom, WSQ/DSQ: a practical

approach for combined querying of databases and the Web, SIGMOD 2000) ,WSMED produces non-materialized adaptive parallel plans based on parameter streams.

• Runtime optimization techniques (A. Gounaris, et al., Robust runtime

optimization of data transfer in queries over Web Services, ICDE 2008 ) investigate adaptation of buffer sizes in web service calls, not dealing with adaptive parallelism on web service calls.

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Conclusion• WSMED can be accessed :

– through a URL http://udbl2.it.uu.se/WSMED/wsmed.html – without installing any software.

• Queries are expressed in SQL to dynamically compose data providing web services without any programming.– Makes any web service queryable with SQL

• AFF_APPLYP:– automatically parallelize web service calls.– adapts the process tree at runtime , based on the flow of result

stream without any static cost model.

• Adaptive Parallel plan with AFF_APPLYP makes possible to run expensive queries.

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Future .....

• Generalize the strategy for queries mixed with dependent and independent web service calls, as well bushy trees (Ongoing work)

• Investigate different process arrangement strategies with the algebra operators.

• Setup a benchmark to simulate the parallel invocation of web services.

Thank you for your attention

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24“The un-queried life is not worth living”