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In this document it is our aim to formally compare the Web Service Modeling Ontology (WSMO) [Roman et al., 2004] and the Semantic Web Services ontology OWL-S [Martin et al., 2004] by hand of some well-known examples. For this purpose we consider examples provided by the OWL-S Coalition [Martin et al., 2004b] and some preliminary WSMO use cases defined in [Stollberg & Arroyo, 2004]. WSMO and OWL-S are the most salient initiatives to describe Semantic Web Services, aiming at describing the various aspects related to Semantic Web Services in order to enable the automation of Web Service discovery, composition, interoperation and invocation.
By trying to match the chosen examples in either formalization manually we want to achieve a better understanding how far one can get using either approach, which are the disjoint features, and which compatibilities exist. In this sense, the present document shall refine and substantiate the conceptual comparison we provided in [Lara et al., 2004]
One crucial point for use case specifications is that the authors normally tend to take only into account what is expressible in their own particular formalism. In trying to deploy WSMO and OWL-S, respectively, in Use case scenarios originally designed for the other formalism, this document should be a helpful starting point in detecting mismatches and flaws in both approaches. Eventually this shall lead to a fruitful combination of both or in the conclusion that one simply subsumes the other, respectively. We plan to extend the results of this comparison in the following in the direction of an automatic mapping tool for (syntactic fragments of) web service descriptions in WSMO or OWL-S in either direction.
The comparison presented in this document exposes the relation between the latest stable versions of WSMO and OWL-S, i.e WSMO-Standard v0.2 [Roman et al., 2004] and OWL-S v1.0 [OWL-S, 2004]. The purpose of the comparison is to highlight the conceptual overlaps and conceptual differences between the two specifications. This document is based on previous results in [Lara et al., 2004]. A previous comparison between DAML-S and WSMF is presented. [Flett, 2002].
Section 2 presents some use case examples specified in OWL-S taken from [Martin et al., 2004b] and we analyze which particular features of OWL-S are addressed in the particular examples and which are not. In the following Section 3 we investigate how far we can get in formulating these examples in WSMO highligting differences between the two formalisms, difficulties, and general patterns which can be recognized from these manual translations. Section 4 and Section 5 will cover the other way from WSMO to OWL based on the WSMO use case examples from [Stollberg & Arroyo, 2004]. In Section 6 we elaborate a more on the lack of a logical formalism for representing conditions, rules and variables in OWL which hampers the specification of complex services in OWL-S. Since the conctrete formalism to be chosen for this purpose is still left open in the current version of OWL as, we will discuss the most likely candidates DRS and SWRL briefly and compare their expressive and syntactic features with F-Logic, the proposed logical formalism underlying WSMO. In order to exemplify the difference we again chose some examples from ???(Rules examples from: ORL (=SWRL) copy paste by Ian Horrocks, reference?) and [Stollberg & Arroyo, 2004] We will summarize and discuss our findings in Section 7 pinpointing to open questions. Finally, we conclude with an outlook to further work in Section 8.
In this section we describe the examples that accompany the version 1.0 of OWL-S [Martin et al., 2004b]. Two examples are given by the OWL-S Coalition in order to illustrate the use of the service ontology, namely:
In the next subsections, we summarize the most important aspects of the examples. For more details (including the OWL files for the examples), we refer the reader to [Martin et al., 2004b].
This example models a Web Service for gathering information about fligths and booking the selected flight.
Grounding (WSDL grounding provided for the example):
This example models two Web Services that offer the electronic purchase of books: the ExpressCongoBuy service and the FullCongoBuy service. We will first present the express version of the service, a one-step form, CongoBuy, with the service treated as atomic; i.e., no interactions between buying and selling agents are required, apart from invocation of the service and receipt of its outputs by the buyer. Given certain inputs and preconditions, the service provides certain outputs and has specific effects [Martin et al., 2004b].
Grounding (WSDL grounding provided for the example):
The Full version of the Congo example shows its composition from its component services. The full-fledged version of the service, FullCongoBuy, includes an arrangement of subprocesses LocateBook, PutInCart, SignIn, CreateAcct, CreateProfile, LoadProfile, SpecifyDeliveryDetails, and FinalizeBuy each, with its own specification of inputs and outputs [Martin et al., 2004b].
Grounding (WSDL grounding provided for the example):
In this section, we use the Web Service Modeling Ontology WSMO-Standard v0.2 [Roman et al., 2004] to model the examples described in the previous section.
The OWL-S examples assume the homogeneity of the terminologies (domain ontologies) used to describe the Web Services. As a consequence, the ooMediators in WSMO-Standard are not necessary to model the examples given.
Regarding wwMediators, they would be used to define the decomposition of the service, i.e. the WSMO-Standard orchestration. Unfortunately, the current version of WSMO-Standard does not sufficiently define how the orchestration is described, which makes the use of wwMediators and the definition of the decomposition of the service not possible. Future versions of WSMO-Standard will define this aspect in detail, and the modelling of the service orchestration will be included in the following versions of this document.
As a consequence, we focus in the following sections on the modelling of WSMO-Standard goals, ggMediators, wgMediators and Web Services for the OWL-S examples presented. We assume that the OWL domain ontologies defined in the examples are valid, and we will not redefine them here.
The OWL-S profile is interpreted as advertising both the capability of the service and the requirements of the requester. As discussed in [Lara et al., 2004], this unified view is split in WSMO-Standard into two different views: the requester view (modelled as a goal) and the provider view (modelled as a capability). Therefore, we start the modelling of the BravoAir service by defining the goal for the requester.
In the OWL-S modelling, the profile of the service is classified using a profile hierarchy. This can be modelled in WSMO-Standard via ggMediators, that can define the reuse and refinement of other goals. Therefore, we will model the profile hierarchy given in the example as a succesive refinement of goals.
Nevertheless, it can be seen that the OWL-S profile hierarchy does not define real profiles i.e. does not define the IOPEs of the service, but a taxonomy of profiles. In WSMO-Standard, this taxonomy is defined by REAL goals i.e. the categorization is given by the use and refinement of existing goals.
In order to give a more accurate idea of the use of goals and ggMediators in WSMO-Standard, we will sligthly adapt the OWL-S example. We will assume that the properties defined for the profile hierarchy, such as merchandise or deliveryMode, mean that the profile describes an effect of performing a purchase and having the goods delivered, and we will model them as effects in the goal. The OWL-S taxonomy could be defined using subclassing of goals, but this is not the intended use of goals and ggMediators in WSMO-Standard.
In the following, we model the taxonomy defined in the OWL-S profile hierarchy using goals and ggMediators.
effects ->> eCommerceEffect
definedBy -> X:purchase[goodType -> product], Y:delivery[deliveryMode -> transportation]
usedMediators ->> eCommerceAirlineTicketingMediator
sourceComponent -> eCommerceGoal
targetComponent -> airlineTicketingGoal
reduction -> airlineTicketingReduction
definedBy -> X:purchase[goodType -> AirlineTicket]
Once the goals and their relationship are defined, we will model the actual Web Service and link it to the appropriate goal using a wgMediator.
nonFunctionalProperties -> nonFunctionalPropertiesBravoAir
capability -> capabilityBravoAir
interfaces ->> interfaceBravoAir
title -> "BravoAir Web Service"
subject -> naics561599
description -> "The service provides flight reservations based on the specification of a flight request. This typically involves a departure airport, an arrival airport, a departure date, and if a return trip is required, a return date. If the desired flight is available, an itinerary and reservation number will be returned."
publisher -> reservationDepartment
identifier -> "http://www.deri.at/FormalComparison/Examples/BravoAir"
source -> "http://www.daml.org/services/"
performance -> goodRating
reliability -> goodRating
security -> goodRating
scalability -> goodRating
robustness -> goodRating
accuracy -> goodRating
networkRelatedQoS -> goodRating
Notice that some non-functional properties that are available in WSMO-Standard but that are not defined in the OWL-S example, have not been used.
Some values, such as naics561599, reservationDepartment or goodRating are defined as instances of the appropriate domain ontologies. The exact definition of these instances and the correspondent ontologies is out of the scope of this document.
In the OWL-S modelling of the BravoAir non-functional properties, two contacts and two categorizations are described. However, the cardinality constrainsts in WSMO-Standard do not allow the definition of more than one value for the non-functional properties of the service.
The contact information given in the OWL-S example has been included as the publisher of the service. It can be argued that it could also be the creator or either the contributor, but with the information available about the OWL-S example, defining the contact information as the publisher seems to be the original intention of the authors.
The OWL-S modelling includes information about the geographical radius of the service. There is not such a non-functional property in WSMO-Standard.
The rating property in OWL-S could be interpreted in different ways. As WSMO-Standard provides a more detailed non-functional characterization of the service, we chose to interpret the rating given in the example as representing several non-functional aspects of the service, such as performance, reliability, security, etc. In general, a service modelled using WSMO-Standard will describe specific values for each of these properties.
usedMediators ->> airlineTicketingBravoAirMediator
preconditions ->> bravoAirPrecondition
postconditions ->> bravoAirPostcondition
effects ->> bravoAirEffect
We do not define non-functional properties for the capability because this information is not defined in the OWL-S example. However, for other use cases, they could be used.
As discussed before, we do not define ooMediators because in the example homogeneity of terminologies is assumed.
sourceComponent -> airlineTicketingGoal
targetComponent -> capabilityBravoAir
reduction -> bravoAirReduction
The reduction includes the postconditions that are defined by the BravoAir capability but not defined in the goal, stating the difference of functionality between the goal and the service.
definedBy -> O1:output, O1:preferredFlightItinerary_Out, O2:output, O2:acctName_Out, O3:output, O3:reservationID_Out
definedBy -> I1:input, I1:departureAirport_In, I2:input, I2:arrivalAirport_In, I3:input, I3:outboundDate_In, I4:input, I4:inboundDate_In, I5:input, I5:roundTrip_In, I6:input, I6:preferredFlightItinerary_In, I7:input, I7:availableFlightItineraryList_Out, I8:input, I8:acctName_In, I9:input, I9:password_In, I10:input, I10:reservationID_In, I11:input, I11:confirm_In
definedBy -> O1:output, O1:preferredFlightItinerary_Out, O2:output, O2:acctName_Out, O3:output, O3:reservationID_Out ]
In WSMO-Standard, the postcondition defines the relationship between the input and the output. However, as this information is not capture in OWL-S, it cannot be extracted from the BravoAir example. For that reason, we cannot include that information here, although it is necessary to completely describe the functionality of the service.
definedBy -> X:purchase[goodType -> airlineTicket], Y:delivery[deliveryMode -> transportation] ]
It can be seen that the BravoAir effect has been sligthly adapted from the OWL-S example, in order to make it consistent with the interpretation of the service effect given for the goal.
choreography => choreographyBravoAir
orchestration => orchestrationBravoAir
Non-functional properties and used mediators are not defined for the interface for the same reasons they were not defined for the capability. Regarding the choreography and orchestration, the current version of WSMO-Standard does not provide the required modeling elements to describe them yet. Future versions of WSMO-Standard will define the required modeling elements and the details of the choreography and orchestration of the BravoAir Web Service will be added to this document.
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[Flett, 2002] A. Flett: A comparison of DAML-S and WSMF, Technical report, 2002.
[Keller et al., to appear] U. Keller, A. Polleres, R. Lara, and Y. Ding: Language Evaluation and Comparison, to appear.
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[Roman et al., 2004] D. Roman, U. Keller, H. Lausen (eds.): Web Service Modeling Ontology - Standard (WSMO - Standard), version 0.2 available at http://www.wsmo.org/2004/d2/v02/index.html
[Stollberg & Arroyo, 2004] M. Stollberg, S. Arroyo (eds.): WSMO Use Case Modeling and Testing, version 0.1 available at http://wsmo.org/2004/d3/d3.2/index.html
The work is funded by the European Commission under the projects DIP, Knowledge Web, Ontoweb, SEKT, SWWS, Esperonto, COG and h-TechSight; by Science Foundation Ireland under the DERI-Lion project; and by the Vienna city government under the CoOperate programme.
The editors would like to thank to all the members of the WSMO working group for their advice and input to this document.
 There is a mistake in the example, as the Service definition refers to Profile_Congo_BookBuying_Service via the presents property, but the real profile that references the service via the presentedBy property is Profile_Full_Congo_BookBuying_Service.
 There is a mistake in the example. SignInSequence is defined as atomic in the choice definition, although this process is defined as a composite process later on. We will consider it as a composite process, as this seems to be the intention of the authors.
 The CreateProfile process is not defined in the example.