The Web Service Level Agreement (WSLA) is a Web. Service specification language developed to provide a SLA template to capture all the information negoti-.
2008 IEEE International Conference on Services Computing
WSLA+: Web Service Level Agreement Language for Collaborations Surya Nepal, John Zic, Shiping Chen Networking Technologies Laboratory, CSIRO ICT Centre, Australia Cnr Vimiera & Pembroke Rds, Marsfield NSW 2122, Australia {FirstName.LastName}@csiro.au sible to define and share resources as web services in a dynamic collaboration. In a dynamic collaboration, all participating enterprises contribute resources and they must agree with each other’s contributions. The contributions and agreements are captured in a document called an eContract [2]. Keller and Ludwig [5] defined a WSLA framework for defining and monitoring SLAs between service providers and service consumers. This framework works well in the electronic commerce (eCommerce) types of scenarios that involve two parties with distinct roles; the service provider offering a service and the service consumer requesting and consuming the service. However, in the context of dynamic collaborations, this does not work well due to the following unique characteristics of dynamic collaborations. • Contributions – all parties in the collaboration contribute multiple services leading to a Multi Parties Multi Services (MPMS) scenario. • Roles – all parties in the dynamic collaboration are both service providers and service consumers leading to a Multi Roles (MR) scenario. A party plays a role of service provider for providing its services and a service consumer for consuming services provided by other parties. This contrasts to the eCommerce scenarios where there are two distinct roles: provider and consumer. • Agreements – all parties in the dynamic collaboration must agree with each other’s contributions, unlike the usual eCommerce scenario where a service consumer agrees with the offers made by the service provider. In order to fulfill these requirements, this paper presents the Web Service Level Agreement Language for collaboration, called WSLA+ that extends and modifies the basic language structures of WSLA. WSLA+ enables collaborating partners to unambiguously define a wide variety of SLAs for all the services contributed to the collaboration. In this paper, we describe the language using an example of a dy-
Abstract The Web Service Level Agreement (WSLA) is a Web Service specification language developed to provide a SLA template to capture all the information negotiated and agreed upon by a service provider and service consumer. Though this specification is suitable for many Business-to-Business collaborations involving two parties, it does not fulfil the requirement of a new business model involving multiple parties, where a party provides multiple services to other parties and consumes services provided by other parties. To address this requirement, this paper proposes an extension to the WSLA language to capture multi-party collaborations, called WSLA+. Keywords: Dynamic Collaborations, Service Level Agreements, Virtual Organisation, WSLA.
1. Introduction In recent years, enterprises have been exploring a new business model that effectively combines and utilizes their own services with other external services (including those from competing enterprises) to create new business alliances. Collaborations built around this concept are termed dynamic collaborations. With the emergence of global nature of the enterprises, business organizations have started adopting this style of collaboration. Web Services are becoming the prominent paradigm to support this new business model through mechanisms and standards for service publishing, discovery, negotiation, as well as on-demand provisioning, binding and execution of services based on service level agreements (SLAs). Recently, resources such as storage and networking infrastructures, tools, software and data are implemented using Web Services technologies so that they can be made available as services to users. For example, a concept of Software-as-a-Service (SaaS) is introduced for software [6] and Infrastructure-as-a-Service (IaaS) for storage and networking infrastructure[3]. Therefore, it is pos-
978-0-7695-3283-7/08 $25.00 © 2008 IEEE DOI 10.1109/SCC.2008.66
485
namic collaboration from the movie post-production industry, where each production house contributes unique services that collectively enable the production of a movie.
of any deployment of resources and enforcement of access policies and other obligations. In a simple electronic commerce scenario, a SLA is signed between the service provider and the consumer when the agreement is reached. In some cases, a SLA might need to be renegotiated in order to satisfy both parties. During the negotiation process, a SLA template is created with a set of service parameters that would be negotiated between two parties. WSLA is the SLA template suggested for use in this model. We develop our extensions to WSLA for an eContract in a dynamic collaboration and present the resulting eContract template and an example of its use.
2. Motivation Dynamic collaborations bring together complementary sets of competencies from competing enterprises to address new market opportunities in a rapidly evolving global economy [1]. In addition to enterprise applications, dynamic collaborations between cross-organizational entities occur in other application domains such as Global Command and Control Systems in military application, coalitions formed among civilian organizations as responses to emergency situations, coalitions between researchers in different institutions for eResearch applications and health care facility and practitioners’ coalitions for eHealth applications. The valuable contributions of dynamic collaboration technologies have been recognized by both industries and governments as evident from the special issue Journal on Dynamic Collaboration by NEC [1], and DARPA funded research in dynamic collaboration.
3. WSLA+ Figure 2 shows the UML diagram depicting some of the main concepts and their relationships. The following concepts and relationships differentiate WSLA+ from WSLA. Multiple Parties - The contract in WSLA+ language supports participation of multiple parties as compared to two parties. For example, three autonomous, distributed postproduction houses are involved in our example. Multiple Services – The WSLA+ supports multiple services. Unlike WSLA where the service provider offers all services, WSLA+ enables all parties to contribute services towards the collaboration. For example, LA Studio provides storage service and video specialist service whereas Sydney Studio provides printer and application service. Multiple Roles – In WSLA, a party can play one of the three distinct roles: service provider, service consumer and supporting party. In WSLA+, a party can play multiple roles. For example, LA Studio consumes an application service offered by Sydney Studio and provides a storage service to other parties. Multi Hop Negotiation/Agreement– A contract may need to be transferred through multiple hops before reaching an agreement. For example, LA Studio can contribute a number of services, and sends the contract to Sydney Studio. The Sydney Studio may agree with the contributions of LA Studio, make its own contributions and send the contract to Tokyo Studio. Tokyo Studio may agree with the contributions of LA and Sydney and sends the contract back to LA. LA Studio needs to know who has agreed with whose contributions within the contract. In WSLA+, such agreements are captured explicitly in the contract. This enables different types of negotiation and agreement protocols among collaborators within dynamic collaboration.
Figure 1 An Example of Dynamic Collaboration in a movie postproduction industry Figure 1 shows an example of a dynamic collaboration among three distributed, autonomous postproduction houses in order to produce a movie. As can be seen in the figure, three companies contribute different resources as services in the collaboration. The contributed services include Audio Visual editing service, Audio Visual application service, storage service, printer service, computation service as well as the services of audio video specialists. The collaboration also uses external third party provided services such as contract service and network service. One of the key features in the collaboration is the eContract negotiated between the collaborators ahead
486
Figure 2 WSLA+ concepts and relationships. The differences with WSLA are shown in a different colour. The contract is defined as WSLAType as follows. age SLAs for each service contributed, and (c) partici pants who provide the resource services on behalf of the signatory participants. pants, LA Studio, Sydney Studio and Tokyo Studio, which are declared in lines 1-7. There are two support vanco. The dynamic collaboration service is a third party service provider that offers a contract service to the collaboration. This service is purchased and sponAs shown in the above XML snippet, the contract sored by Sydney Studio, as shown in lines 8-9. The comprises of four major components as follows. vanco is also a third party service provider that offers Participants – describe the multiple parties involve in a virtual network service to the collaboration. This collaboration. There are two types of participants: sigservice is purchased and sponsored to the collaboranatory participants and supporting participants. The tion by Tokyo Studio as shown in lines 10-11. In addinegotiators chosen by participating organizations to tion to Web Services resources, the signatory negotiate a contract are categorized as signatory parparticipants also contribute human resources to the ticipants; whereas participants without signatory aucollaboration. This is illustrated through a contribution thorities are categorized as supporting participants and of a graphic designer John McCain by the Sydney are sponsored by one of the signatory participants. The Studio (shown in lines 12-13). supporting participants include (a) participants from 1. 2.
the same organisation that are involved in the collaboration, but do not have delegation to be a signatory participant, (b) participants used to monitor and man-
487
Sydney RD Sydney
3. 4. 5. 6. 7. 8.
9. 10.
11. 12.
13. 14.
… … SydneyStudio ResourceService TokyoStudio ResourceService SydneyStudio ResourceService
