D1 Report on landscapes of existing service description efforts by Daniel Oberle
There exists a plethora of service description efforts that can be grouped into different strands summarized in the table below. Each of the strands has its own motivation and representation needs for capturing service information. The individual efforts can be attributed to the following criteria: (i) whether the scope of the effort lies in capturing IT or business aspects of services or the whole service system. (ii) the purpose of the corresponding effort - is the effort geared towards normative data exchange, is it there to facilitate software engineering, is it there to automate a specific task, or is it there to act as reference model? (iii) whether the effort is able to capture business network relationships between services. (iv) whether the effort is standardized.
|1. Service Oriented Architectures|
|SOA Ontology||IT/ Business||Reference||No||OWL||Open Group|
|Core Ontology of Web Services||IT||Reference||No||OWL||No|
|2. Semantic Web Services|
|Reference Service Model||IT||Reference||No||OWL||No|
|Minimal Service Model||IT||Exchange, Automation||No||RDFS||No|
|4. Service Networks|
|OBELIX service ontology||Business||Configuration||Yes||RDFS||No|
|5. Service System|
|Reference Architecture Foundation of SOA||System||Reference||No||UML||OASIS|
|Service Design Model||System||Engineering||No||ECore||No|
|Ontological Foundations of Service Science||System||Reference||No||FOL||No|
|TEXO Service Ontology||System/Business||Reference||No||OWL||No|
|DIN PAS 1018||Business||Exchange||No||Informal||DIN|
|USDL||Business||Reference / Exchange / Engineering||No||ECore, XML||In progress|
The first strand of service description efforts is the field of Service-oriented Architectures (SOA). SOA is a way of thinking about IT assets as service components, i.e., functions in a large application are factorized in stand-alone services that can be accessed separately. Because of their IT focus, most approaches limit their attention to the field of software architecture. Originally, several standards bodies specified several dozens of different aspects which are collectively known as WS-* (incl. WSDL, WS-Policy, WS-Security, etc.). Since one of the key components of a SOA is a service registry, the OASIS standards body introduced the concept of Universal Description, Discovery and Integration (UDDI), i.e., a specification for a platform-independent registry. UDDI services shall be discovered via white pages (address, contact, and known identifiers) or yellow pages (industrial categorizations based on standard taxonomies), as well as green pages. However, UDDI does hardly prescribe any schema for such information. As the concept of SOA matured, calls for support in software and service engineering increased. Hence, the OMG standards body dedicated its focus to software engineering for SOA, and, subsequently defined the Service-oriented architecture Modeling Language (SoaML). SoaML actually orginates in the publicly funded EU research projects SHAPE and MODELWARE (Berre 2009). The predecessor which led to the SoaML is the UML Profile and Metamodel for Services (UPMS, (Berre 2008)). Finally, the multitude of description efforts and different definitions of SOA led to a Reference Model for Service Oriented Architecture (SOA-RM) from OASIS (MacKenzie et al. 2006). Similarly, The Open Group drafts an alternative reference model in form of an ontology for Service-Oriented Architectures (SOA Ontology) (Harding 2008).
Current research in the SOA strand mainly concerns RESTful services and their description. Until recently there was no counterpart to WSDL for RESTful services. The W3C submission Web Application Description Language (WADL) is about to fill this gap (Hadley 2009). Note, however, that version 2.0 of WSDL can be used to describe REST Web services, thus competing with WADL. Another recent research is the work of (Oberle et al. 2006) provides an ontological account of Web services. The resulting core ontology of web services is built according to the principles of ontological analysis on top of the DOLCE foundational ontology, and, thus, can also be regarded as a reference model.
Semantic Web Services Efforts
A second strand consists mainly of ontologies in the field of Semantic Web Services. As presented in the seminal paper, viz., (McIlraith et al. 2001), the main goal of Semantic Web Services approaches is automation of discovery, composition, and invocation of services in a SOA by ontology reasoners and planning algorithms. The most prominent efforts are OWL-S (Ankolekar et al. 2001) and WSMO (Roman et al. 2006). Many surrounding and similar efforts have surfaced in literature. For example, (Dobson, Sánchez-Macián) try to unify existing ontologies that capture qualities-of-services in order to automate service discovery. Considering the need to attach semantic descriptions to existing WS-* descriptions and the multitude of ontologies available, the W3C came up with a recommendation called Semantic Annotations for WSDL (SAWSDL) (Farell, Lausen 2007). SAWSDL introduces XML attributes to establish correspondences between tags in WSDL (or arbitrary XML Schema documents) and concepts or relations in an arbitrary ontology. A similar idea to SAWSDL is already adopted by the W3C Member Submission called Semantic Annotations for REST (SA-REST) (Gomadam et al. 2010). SA-REST defines three basic properties that can be used to non-intrusively annotate HTML/XHTML documents, typically to embed ontological meta-data. These properties are included as part of the XHTML document allowing a capable processor to gain extra information about the content of the document.
With the many approaches around came the need to specify a reference model for semantic SOAs. Consequently, the OASIS is also about to specify a Reference Ontology for Semantic Service Oriented Architectures (RO-SOA) (Norton et al. 2008). There also is the recent Reference Service Model (RSM) (Loutas et al. 2011) for the Web of Services that aims to close the gap between two phenomenically contradictory service annotation paradigms: traditional semantic service frameworks and the emerging social annotation of services. RSM aims to (i) facilitate the semantic interlinking between services annotated using different semantic models and (ii) accommodate the bottom-up social annotation of services. RSM was developed following the design science research methodology. To develop RSM, existing semantic service models and SOA service models were reviewed in the light of the six service contracts and examined whether and using which elements each of the models supports in each of the contracts. The identified elements were then fed to a multiphase abstraction exercise. RSM comprises of the following concepts: Service, Service Input, Service Output, Service Context and Service Logic, Service Provider, Service Client and Service Feedback.
Current research topics of this strand tackle the new concepts of Linked Open Data, RESTful services, and Linked Services (Pedrinaci, Domingue 2010). Consequently, the ongoing publicly funded research project SOA4All brought forth WSMO-Lite (Lightweight Semantic Descriptions for Services on the Web) which is in W3C Member Submission state (Fensel 2010). WSMO-Lite consists of only 5 classes to structure the capturing of service semantics in terms of non-functional properties, effects, conditions, and functional classifications. The original purpose of WSMO, namely the automation of discovery and execution, did not change, however. MicroWSMO (Kopecky et al. 2008, Kopecky et al. 2011) is another approach to tackling RESTful services and Web APIs. MicroWSMO is relevant on the syntax level on top of HTML adding "hooks" for pointing to concepts and lifting and lowering definitions. It is similar to SA-REST but relies on a different serialisation (microformat) and acknowledges the need for a service model. The latter is captured in the Minimal Service Model (Pedrinaci, Domingue 2010). This model essentially captures the basic notions of a Web service from a technical point of view. The minimal service model can be used to bring together MicroWSMO, SAWSDL, WSMO-Lite, OWL-S, etc., for instance. It is essentially an integration ontology that covers the basic functional notions of services and is largely a subset of all other service ontologies such as WSMO, OWL-S, etc.
The third strand is rooted in the rise of on-demand applications that led to the notion of software-as-a-service (SaaS), covering software applications (e.g., CRM on-demand) and business process outsourcing (e.g., gross-to-payroll processing, insurance claims processing) to cloud and platform services. The emphasis of service here implies that the consumer gets the designated functionality he/she requested together with hosting through a pay-per-use model. Thus, software-as-a-service is not synonymous with SOA. The strand of SaaS contains a standard, namely, the W3C recommendation called SML (Service Modeling Language) (Pandit et al. 2009). SML is a strict superset of XML Schema adding the capability to define constraints on a model (using Schematron rules) and the capability to define and reference model elements in separate files. In addition, SML-IF defines an exchange format so that SML model instances can be easily exchanged between producers and consumers. One anticipated use for SML is to define a consistent way to express how computer networks, applications, servers, and other IT resources are described or modeled so businesses can more easily manage the services that are built on these resources. Therefore, we have classified it in the SaaS strand. Note however, that the use of SML is not limited to SaaS scenarios. Current research is represented by the Software-as-a-Service Description Language (SaaS-DL). SaaS-DL builds on WS-* to capture SaaS specificities in order to support model-driven engineering (Sun et al. 2007).
Service Network Efforts
The fourth strand draws attention mainly to describing Service Networks, i.e., the ecosystem and value chain relationships between services of economic value. So far, this strand did not output any standards and is represented by academic approaches only. An early work is (Baida et al. 2001) which is continued by the ontology of the publicly funded EU research project OBELIX by (Akkermans et al. 2004). The latter is an application ontology that helps users with configuration of service bundling and graphical modeling of service networks. The work continued in (De Kinderen and Gordijn 2008a; De Kinderen and Gordijn 2008b) introduces the e3Service ontology (Akkermans et al. 2004) to model services from the perspective of the user needs. This offers constructs for service marketing, but in a computational way, such that automated reasoning support can be developed to match consumer needs with IT-services. The main focus of this work is to generate service bundles under the consideration of customer needs. Another work by the same group is called e3Value ontology (Gordijn, Akkermans 2001) which focusses on value chains and value exchanges between actors and market segments focussed on business modeling and its analysis. (Bitsaki et al. 2008) introduce the Service Network Notation (SNN) which captures similar aspects to the e³Service ontology. However, SNN is an UML model that can be analyzed for measurements of added value for each single participant as well as for the whole network optimization of value flows.
Service System Efforts
Fifth, there are overarching efforts that concentrate on the bigger picture of service systems or service science also taking into account socio-economic aspects. (Alter 2008) was one of the first to realize that the concept of a service system is not well articulated in the service literature. Therefore, he contributes three informal frameworks as a first attempt to define the fundamentals of service systems. Although the background of the OASIS Reference Architecture Foundation for SOAs (Estefan et al. 2009) is Service-oriented architectures, the specification argues that SOA-based systems are better thought of as ecosystems rather than stand-alone software products. Therefore, the specification is put into the service system category and is directly related to the ontological foundations of service science approach. However, the reference architecture foundation is not based on ontological analysis but takes the OASIS SOA-RM as its starting point by building on its vocabulary of important terms and concepts. Another effort considering the wider scope of the service system is the Service Design Model of (Dhanesha et al. 2009). Other than the aforementioned efforts, the Service Design Model is geared at a software engineering purpose and comes in the form of an ECore model for the Eclipse Modeling Framework (EMF). The model takes into account the business organization, the customer, and the delivery organization during service design. The model aims at providing a foundation for the design for service quality by envisioning different modules (such as financial, resource, process, etc.), configurability, variability, and extensibility. Current research in this strand is represented by the work of (Ferrario and Guarino 2008) which can be seen as a continuation and formalization of Alter’s approach. Although differing in its main notions, they present a reference ontology for ontological foundations of service science which is founded on the basic principles of ontological analysis. In turn, this reference ontology forms the core part of the TEXO Service Ontology which extends it by ontology modules for pricing, legal, innovation, or rating information (Oberle et al. 2009). This ontology is outcome of the German lighthouse research project called THESEUS/TEXO.
The final strand is driven by schools of business administration and business informatics and focuses on capturing the purely economic aspects of services regardless of their nature (with less or no focus on IT services and software architectures). Led by the Fraunhofer IAO research institute, the German standard DIN PAS 1018 essentially prescribes a form for the description of services for tendering. The structure is specified in a non-machine-readable way by introducing mandatory and optional, non-functional attributes specified in natural language, such as, classification, resources, location, etc. The standard is driven by needs of the services industry in Germany whose expectations are the professionalization and industrialization of the service industry, the increase of transparency, and eventually the overall development of the service economy. The PhD thesis of Emmrich (2005) has a similar motivation only that this work focuses on product-related services, such as maintenance, and is specified in UML. He basically merges existing standards and models for products, companies, organization, and resources. The PhD thesis of (O’Sullivan 2006) adopts a wider scope and contributes a domain independent taxonomy that is capable of representing the non-functional properties of conventional, electronic and web services. The work compiles the non-functional properties into a series of 80 conceptual models that are categorized according to availability (both temporal and locative), payment, price, discounts, obligations, rights, penalties, trust, security, and quality. The motivation is to provide a reference model for automated service discovery, comparison, selection, and substitution. ORM (Object-Role Modeling) is used to represent the results also available as XML Schema serialization. Toma (Toma 2010) presents a syntactic translation of O’Sullivan’s work in the proprietary WSML language. The goal is to extend the aforementioned WSMO by non-functional properties for automation of discovery, composition, invocation, and, in particular, ranking of services in a SOA (Toma et al. 2008).
Here, the Unified Service Description Language (USDL) continues by further formalizing and extending the economic approaches. USDL is ongoing research contributed mainly by the TEXO project within the THESEUS research program initiated by the German Federal Ministry of Economy and Technology, projects funded by the German Federal Ministry of Education and Research projects (e.g., Premium Services), as well as EU DG INFSO projects (e.g., FAST, RESERVOIR, MASTER, ServFace, SHAPE, SLA@SOI, SOA4ALL), and the Australian Smart Services CRC.
USDL builds on and acknowledges the standards for the technical IT description efforts for services such as WSDL. However, USDL adds business and operational information on top. In order to achieve this, USDL defines normative UML modules (via the Eclipse Modeling Framework (EMF)) for capturing the "master data" of a service. That includes normative modules, i.e., class models for pricing, legal, functional, participants, interaction and SLA aspects. Therefore, both manual and IT services can be described with USDL. Detailed specifications of each module can be found here.
Unlike any of the other approaches USDL serves a reference purpose, its class models can be used to facilitate model-driven software engineering, and its XSD can be used for information exchange. However, it is mainly the content and normative character of the USDL modules that sets USDL apart from many of the related approaches discussed above. For example, UDDI, WSMO, or OWL-S only prescribe tiny schemata and leave the modeling of service description concepts (such as a generic schema for defining a price model or licenses) to the user. Both W3C SAWSDL and W3C SA-REST are designed to be agnostic of any service description schema. Similar holds for W3C SML.
In order to further show the progression compared to the state-of-the-art, one has to compare USDL on the basis of its individual modules to the plethora of related approaches above. For instance, The pricing module progresses the state-of-the-art compared to (i) the state-of-the-art above and (ii) additional related work of price models independent of the service domain such as (Kelkar et al. 2002) for electronic product catalogs. Therefore, the USDL price model provides a scientific contribution in itself as presented in (Kiemes et al. 2010). Regarding (i), the USDL pricing module allows tiered pricing and a structuring in price components according to established business literature. Both is not possible in (O’Sullivan 2006) and (Toma 2010), for instance. In (De Kinderen and Gordijn 2008a; De Kinderen and Gordijn 2008b), the price model is represented as a mathematical formula included as string in the ontology in order to enable the price determination. Therefore, the work is not directly comparable to ours since the structure of a price plan is not declaratively modeled as discussed in (de Miranda and Baida 2006). Regarding (ii) we refer the reader to (Kiemes et al. 2010), where related approaches are grouped and positioned in four categories (a) economic contributions, (b) established enterprise software, (c) standalone billing engines, and (d) explicitly specified pricing models.
Regarding the Legal Module we surpass (i) (O’Sullivan 2006), and, consequently (Toma 2010) since both are not based on a generic copyright model in a specific legal code. Therefore, they also do not consider geopolitical differences in copyright law. One of the most detailed approaches in dealing with service licensing is from (Gangadharan et al. 2007). They developed a service license model considering traditional software licenses. Based on this model, they have created an ODRL (Open Digital Rights Language) Service Profile (ODRL-S), which can be used to describe service licenses. The service model incorporates the WIPO framework and, therefore, lacks a profound legal foundation. (Speiser 2009) talks about usage policies instead of licenses and identifies different kinds of usage policies. His focus lies on the technical formalization of such usage policies, without any legal foundation. With respect to the body of related work of (ii) we refer the reader to the positioning given in (Baumann and Loes 2010). In general, the domain of services is more diverse than the product domain.
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