Request/Response Aspects for Web Services - Advanced Information Systems Engineering - page 630

Fig. 1. Web service invocations with aspects

weaving of aspects. At the client side, mainly an API is provided that offers
methods for interacting with the server component.
The interaction between a client and the framework is as follows. First, the
client's Aspect-API asks the aspect configurators at the web services S 1 and S 2
whether they support the needed aspect (Figure 1: steps a and b). If both sites
support the aspect and respond accordingly, then the aspect is added by the
client (steps c and d) into the response of S 1 and the request of S 2 . When the
actual SOAP request is sent to Service S 1 (step 1), it is answered by the response
message (step 2). Then, the client forwards the request (step 3) to Service S 2
that due to the request aspect can process the request and eventually responds
(step 4). In our use case for data transfer, an aspect that supports direct and
ecient data transmission from Service S 1 to Service S 2 will be used. Due to
the use of request/response aspects, the response message of Service S 1 does
not include the data D in this scenario, since the aspects enable the direct data
transmission of data D to Service S 2 .

3.2 Pointcut Description

A request/response aspect for web services is defined by the following tuple:

A = {P , O , F , M , I , K , D , C} .

( porttype ) defines the qualified name (QName) of the web service porttype
the aspect should be applied to. This element is required to cope with a wild-
card operator, meaning that all porttypes within a service are relevant for this
particular aspect.

P

( operation ) specifies the name of the operation of the given
porttype. A support for a wildcard operator is also needed.

O

( field ) determines
the actual WSDL message part the aspect should be applied to. Since XML
schema elements can be nested complex data types, this field is realized as an
XPath expression[24] , in case the aspect should be applied only to a particular
part of a complex type. The XPath language also allows the use of wildcard
operators and thus enables the application of the aspect to multiple elements or
to multiple parts of (multiple) elements.

F

M ( mode ) is an element of the enu-

meration containing the values . The first one means

that the aspect is applied to the request message, the same holds for response .
When the mode is set to both , the aspect is applied to the request as well as to

{ request , response , both }