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this is achieved at the expense of transferring the control flow to the proxy
architecture that in this way represents a hidden orchestration layer, whereas in
our approach it remains at the orchestration engine.
DJCutter [16] is a framework that provides remote pointcuts as a new lan-
guage construct for distributed aspect-oriented programming. While an aspect is
distributed to remote machines, it only notifies a central server when a pointcut
becomes active. In turn, this server executes the corresponding advice. Refer-
ring to the data transfer example again, the data must first be transferred to
the server that processes it and afterwards transferred back. This will certainly
undo the desired performance gain.
Baligand and Monfort [4] present a framework to separate crosscutting con-
cerns within the service implementation, but do not deal with crosscutting con-
cerns over multiple services or hosts. Their focus is on the weaving of aspects
into the (Java) byte code of the service implementation. Thus, they pin the
presented framework to web services implemented in Java, whereas request/re-
sponse aspects operate on the message level. This allows us to be independent
of the concrete implementation language of a service.
AWED [15] is an aspect-oriented programming language with explicit sup-
port for the distribution of aspects and advice. In contrast to request/response
aspects, it operates on Java. However, web services can be implemented in any
programming language, and only their XML-based SOAP-interface is known.
Again, it cannot be assumed that Java is the implementation language of web
services, such that AWED cannot be used in web service environments where
Java is not used as the implementation language.
3 Request/Response Aspects
In this section, the pointcut description for defining request/response aspects in
web service environments and a supporting framework are presented. The point-
cut description is independent of any implementation language, whereas the
framework itself is located at the web service middleware (i.e., a software stack
that provides support for SOAP communication, like Apache Axis [3]) and pro-
vides the capabilities of interpreting pointcuts and applying the corresponding
advice. The framework consists of: 1.) an extension of the web service middle-
ware that enables the weaving of aspects into web services without changing
their implementation or their interface, including an aspect configurator service,
a request/response aspect weaver, and a security manager; 2.) tools that operate
at the client side, in particular for the seamless integration in BPEL workflows.
This framework is an essential prerequisite for writing and weaving request/re-
sponse aspects. By remaining independent of the service implementation, the
framework respects the black-box idea of service-oriented architectures.
3.1 Framework for Request/Response Aspects
The execution of web services is typically performed by an installed middleware,
such as a web service container and a SOAP processor. The underlying idea of
