Modeling of Web Services using Reaction Rules

1. Introduction

Web services provide a communication interface and a workflow management protocol for business systems. Their goal is set to change the Web from a static collection of information, to a dynamic place where different software components (business logics) can be easily integrated (Arroyo et al., 2004). Some of the factors that constrain web services from achieving that goal can be named as follow: when developers try to enrich the existing Web services with some new functionality, they have to implement necessary changes manually, which may lead to potential execution errors; furthermore, business rules, due to their declarative nature, are used for reflecting dynamic changes representing desired alteration in the business process. When business rules are used in a networked business, they are often large and complex, which makes them difficult to manage and change. There is a lack of automatic mechanism for updating Web services based on the business rules changes (Ribaric et al., 2008).

The need for a more straightforward way to express, and manage business rules as a separate part of Web services’ composition has been recognized by researchers for the numerous benefits that it provides (Charfi & Mezini, 2004). However, integrating rule-based systems in a service-oriented environment is a complex task, due to the fact that both worlds have their own paradigms (Rosenberg & Dustdar, 2005). Many different factors involve in this integration. However, the most important one of these factors is the architecture of service oriented systems. In this architecture, layers play a great role. The layering architecture is needed to be represented and deployed in the world of rules which become challenging and could not be simple done. This integration approach should be loosely coupled, meaning that it is reasonable to expose business rules as services. The way of modeling Web services presented in this paper facilitates this integration process, and those services can be more easily integrated in the wider context of modeling orchestration and choreography.

A promising way to solve these problems is to use a high-level modeling approach combined with the use of rules. A modeling approach will allow developers to focus on a problem domain rather than on an implementation technology. This is why we propose using an approach based on Model Driving Engineering (MDE). Although, there have been several attempts to leverage MDE principles to model Web services, they are still very low level oriented, as they again focus on technical details covered either by WSDL (Bezivin et al., 2004) (Vara et al., 2005) or OWL-S (Timm & Gannod, 2005) (Gronmo et al., 2005). The use of rules implying that they are defined in a declarative way, they can dynamically reflect business logic changes at run-time without the need to redesign the whole system. Since Web services are used for integration of business processes of various stakeholders, it is important for them to reflect changes in business logic, or policies, as good as possible.

The solution that we propose is to use rules to represent and model business processes from the perspective of message exchange. That is, our modeling approach enables one to model Web services from the perspective of the underlying business logic regulating how Web services are used regardless of the context where they are used. To do so, our proposal is to leverage message-exchange patterns (MEPs) as an underlying perspective integrated into a Web service modeling language. This perspective has already been recognized by Web service standards (Chinnici et al., 2007), and our contribution is to raise this to the level of models.

As the leading Rule Modeling language we benefit from UML-based Rule Modeling Language (URML) (Lukichev & Wagner, 2006a) for our approach. URML having strong ties with R2ML (REWERSE Rule Markup Language) empowers us to model rules in various languages. URML supports modeling of domain vocabularies in addition to integrity, derivation, production and reaction rules. .Business rules, being similar to natural language rules, are proposed to be modeled by using reaction rules (also known as Event-Condition-Action, ECA, rules) in this paper. Reaction rules will perform a task (Action) under some circumstances (Conditions) if some events (Event) take place and can best describe a business rule.