Hybrid aspects for weaving object-oriented functionality and rule-based knowledge

Abstract

System and Software Engineering LabVrije Universiteit Brussel Maja.D'Hondt @vub.ac.be Viviane Jonckers System and Software Engineering LabVrije Universiteit Brussel Viviane.Jonckers@vub.ac.be ABSTRACT Software applications often consist of implicit knowledge for making decisions or giving advice in addition to objectoriented functionality. A rule-based system can be employed for representing and reasoning with this knowledge. Although several hybrid systems exist that combine objectoriented programming and rule-based reasoning, a survey we conducted reveals that both paradigms are not well integrated and programs are tightly coupled.We propose hybrid aspects for integrating object-oriented programming and rule-based reasoning. As expected, hybrid aspects specify join points where normal execution is interrupted and advice is executed. However, since two different languages are involved, we need join point models for both and advice that activates both. As such, we complement a simple join point model for object-oriented programming with a join point model for rule-based reasoning. Hybrid advice is independent of the interrupted language and sup-ports sending messages as well as activating rules. It uses values of either language transparently.We present OReA, an implementation of hybrid aspects for weaving Smalltalk and a rule-based system. We discuss and illustrate two applications of hybrid aspects.

AO4BPEL: An Aspect-oriented Extension to BPEL

“…Business rules: Business rules [28] are another example of crosscutting concerns, especially those encountered in composite Web Services [14]. In the very competitive business context worldwide, business rules can change frequently [82] due to new partnerships, changing strategies, mergers, etc.…”

“…Assume that these operations return a string result with the vacation package information, the flight information, or accommodation information. The advice (lines [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]) is a sequence activity that executes before the join point activity. At the beginning of the advice, the input parameters of the car rental Web Service are taken from the parent process using the context collection variable ThisProcess(clientrequest) (line 20).…”

“…This hierarchical modularization of the composition specification, according to the aggregation relationships between the Web Services involved, is a powerful tool to master the complexity of composite Web Services. However, it is not the most appropriate modularization schema for crosscutting concerns such as logging, persistence, security, and business rules [9,21,28,31,55,70,85]. Code pertaining to these concerns does not fit well into the process-oriented modular structure of a composite Web Service, because it cuts across the process boundaries.…”

A Flexible Architecture for Enforcing and Composing Policies in a Service-Oriented Environment

“…Other authors have used Aspect-Oriented Programming (AOP) [13] for integrating security and policies with applications [6,24]. AOP is situated at a higher level of abstraction but is less generic, which makes it hard to apply it in a heterogeneous environment.…”

Modularization of Distributed Web Services Using Aspects with Explicit Distribution (AWED)

“…The new general model of AWED is able to support such behavior as illustrated by the code fragment of figure 7. The authentication advice is guaranteed to always execute before other advice that applies to that joinpoint such as, for instance, a billing advice [12]. The billing advice will not be executed when the authentication fails because the authentication advice does not invoke proceed in that case.…”