Information Technology Reference
In-Depth Information
aspect. This information is provided by the workflow developer during the de-
sign of the workflow. If this is the case, the AIH deploys the aspect to the actual
web service and - depending on the defined relevance of the (request/response)
advice - deploys it also to subsequent web services.
5 Evaluation
In this section, the realization of three use cases for request/response aspects
is discussed. First, the use case of ecient data transmission described above
is considered. The goal is to realize ecient data transmission between web
services without additional implementation efforts (except for developing the
aspects themselves once), without changing the web services, and without losing
modularity and decoupling of web services. The second use case is also motivated
by the multimedia workflow and realizes data compression. The third use case
provides a cryptographic data transfer via request/response aspects. This use
case is motivated by a workflow that performs medical analysis.
5.1 Use Case 1: Data Transfer
For the first use case, consider the general design shown in Figure 1 - before the
request of Service
S
2
can be handled by an aspect, the response of Service
S
1
must have been handled by an aspect, too. In this way, the aspect woven into
Service
S
1
implements the
IResponseAdvice
. This implementation first takes
the binary data returned by the service and then creates a new Flex-SwA ref-
erence that points to the data. This reference is encoded into the response to
fit syntactically into the data structure the service returns. After this (response)
message has been passed to Service
S
2
, the aspect woven into this service imple-
ments the
IRequestAdvice
. This implementation expects a Flex-SwA reference
encoded in the data structure the service receives. Then, the encoded reference
is resolved, and the data is transferred.
To test the Flex-SwA advice on a broader variety of data types, three different
service implementations were investigated. The first echo service implementation
works on a byte array, the second service on strings, and the third service uses
SOAP with Attachments. The performance is evaluated using these three web
services and the Flex-SwA advice mentioned before. This specific advice handles
the request as well as the response message of the services and also deals with
their (different) message formats. A client that utilizes the presented framework
only needs to call the aspect configurator service with an aspect (see Listing 1.3)
as an argument. This is all a client has to do in order to perform the weaving of
the aspect for ecient data transmission.
Obviously, it can be expected that the weaving of the Flex-SwA aspect im-
proves the workflow runtime significantly. The tests were performed on three
machines running Fedora Linux. Each machine has the same hardware, namely
an Intel Core 2 Duo E8600, 4 GB of RAM and a 100 MBit/s Ethernet network.
One of these machines operated as the client, whereas the other two hosted the
echo services. Different transmission types and different files sizes were used, but
