Semantic Web Services
Composition
Peter Bartalos
Outline
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Basics of service composition
Why we need semantics?
Different kinds of user goals
Service composition
Arranging web services
into complex workflows
 Based on user goal
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WS1
WS4
WS2
WS5
WS6
WS7
WS3
Service chaining
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Requirement
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I/O compatibility
Syntactic level - WSDL
Ancestor
O
?
I
<element name=“getTemperatureReturn" type="xsd:double"/>
<element name=“areaName" type="xsd:string"/>
Successor
Service chaining
getTemperature()
Output:
meteoowl:Temperature
Input:
meteoowl:Elevation
meteoowl:LocalPressure
getAtmPressure()
Output:
<element name=“getTemperatureReturn" type="xsd:double"/>
Input:
<element name=“elevation" type="xsd:double"/>
<element name=“localPressure" type="xsd:double"/>
Meaningful chaining
getElevation()
Output:
meteoowl:Elevation
Input:
meteoowl:Elevation
meteoowl:LocalPressure
getAtmPressure()
Output:
<element name=“getElevationReturn" type="xsd:double"/>
Input:
<element name=“heightAboveLocation" type="xsd:double"/>
<element name=“localPressure" type="xsd:double"/>
Problem again
getElevation()
Output:
meteoowl:Elevation
Input:
meteoowl:Elevation
meteoowl:LocalPressure
In meters
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In ft.
getAtmPressure()
Output:
<element name=“getElevationReturn" type="xsd:double"/>
Input:
<element name=“heightAboveLocation" type="xsd:double"/>
<element name=“localPressure" type="xsd:double"/>
Problem again
getElevation()
Output:
meteoowl:Elevation
Input:
meteoowl:Elevation
Postcondition:
inMeters (getElevationReturn)
Precondition:
inFeet (heightAboveSeaLevel)
getAtmPressure()
Output:
<element name=“getElevationReturn" type="xsd:double"/>
Input:
<element name=“heightAboveLocation" type="xsd:double"/>
<element name=“localPressure" type="xsd:double"/>
Considering conditions
getElevation()
Output:
meteoowl:Elevation
Input:
meteoowl:Elevation
Postcondition:
inMeters (getElevationReturn)
Precondition:
inMeters (heightAboveSeaLevel)
getAtmPressure()
Output:
<element name=“getElevationReturn" type="xsd:double"/>
Input:
<element name=“heightAboveLocation" type="xsd:double"/>
<element name=“localPressure" type="xsd:double"/>
Semantic service composition
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Basic service description
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I/O
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Binding parameters to the concepts in the ontology
Pre-/post-conditions
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Logical expressions
Predicates combined with logical operators
Binding to ontological elements
Semantic
compatibility evaluation
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Compatibility evaluation
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I/O
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Checking if O subsumes I
Pre-/post-conditions
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Checking if Post => Pre
How it starts
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User goal definition
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Required outputs
Required condition
Provided inputs
How it starts
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User goal example
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The user wants the air pressure in kPa in Smolenice
corrected to sea level.
Required output
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Required condition
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meteoowl:AtmosphericPressure
inkPa(pressure)
Provided inputs
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geoowl:Area = Smolenice
meteoowl:LocalPressure = 98.5kPa
Example composition
Smolenice
Input:
geoowl:Area
getElevation()
Output:
meteoowl:Elevation
98.5kPa
Input:
meteoowl:Elevation
meteoowl:LocalPressure
getAtmPressure()
Output:
meteoowl:AtmosphericPressure
Postcondition:
inkPa(pressure)
Best composition
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Generally we have several composite
services satisfying the user goal
We have to choose the best one
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Soft and hard constraints
Simple condition
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The user wants to book a flight.
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Condition
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booked(flight)
Value restriction
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The user wants to book a flight to Los
Angeles.
Condition
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booked(flight)^hasDestination(flight,
destination)
Value restriction
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destination = LosAngeles
Local variables
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The user wants to book a flight to Los Angeles
and a hotel for overall price at most 500$.
Condition
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Value restriction
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booked(flight)^hasDestination(flight,
destination)^hasPrice(flight,
flightprice)^booked(hotel)^hasPrice(hotel, hotelprice)
destination = LosAngeles ^ price < 500$
Local variable definition
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price = flightprice + hotelprice
Soft constraints - fuzzy
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The user wants to book a flight for about
350$.
Condition
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booked(flight) ^ hasPrice(flight, flightprice)
Value restriction
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flightprice = fuzzy number
Predicate evaluation I
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The user wants to book a flight through
weekend.
Condition
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booked(flight)^hasFlightTime(flighttime)
Value restriction
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isWeekendTime(flighttime)
Predicate evaluation II
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The user wants to book the cheapest
flight.
Condition
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booked(flight) ^ hasPrice(flight, flightprice)
Value restriction
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cheapest(flightprice)
Conditional restriction
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The user wants to book a flight if it
includes also insurance, else he wants to
use a train.
Alternatives
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booked(flight)^includesInsurance(flight)
book(traintravel)
If Then Else …
Event handling
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The user wants to book a flight, but if that flight
is delayed by more than 24 hours, he wants to
cancel the flight and take a train.
Basic condition
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Event
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booked(flight)
booked(flight) ^ isDelayed(flight, delay)
delay > 24hour
Action
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cancelled(flight) ^ booked(traintravel)
Open problems
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How to get the required representation of
the user goal?
How to present the results?
Booking problem …?
Do we need additional metadata?
How to develop “composition friendly”
services?