The default message processing flow for the Access Gateway makes
use of the various mediation primitives in a single sequence or in
a set of sequences.
Upon receipt of a Web service request, the following
mediation primitives are executed in this sequence:
Figure 1. Default Access Gateway mediation
flow
Note: To prevent a warning message when you are utilizing WebSphere® Integration Developer (WID),
the format of the mediation flow has been altered. This has been done
to reduce the size and also improve the performance of the flow execution.
- The Message Element Remover mediation primitive checks the user
principal against the requester exception list. If the requester is
not on the list, and if headers exist, the message element remover
removes the TWSS headers from the request (using the appropriate XPath
selector element).
- The Transaction Identifier mediation primitive adds SOAP headers
with the global transaction ID requester and name. If the global transaction
ID and requester name have already been provided from an upstream
element, then those values are used.
- The Policy Retrieval mediation primitive retrieves the policy
information from the Service Policy Manager.
- If transaction recording is enabled by policy attributes, then
the information about the transaction–such as the unique ID, requester,
service, and operation–is recorded to a database table. (If the transaction
recorder is disabled, then network statistics must also be disabled
because of the database structure.)
- If the Network Statistics mediation primitive is enabled, it records
statistical information about the request. The Transaction Recorder
mediation primitive must be enabled so that Network Statistics can
record the details. The Network Statistics record corresponds to the
Transaction Recorder's transaction ID.
- If applicable, authorization is verified based on requester,
service requested, and operation.
- The request is checked to verify that it is a Parlay
X request whose parameters may contain a list of URIs, some of which
may be groups.
- If it is not such a Parlay X request, skip to step 9.
- If it is such a Parlay X request, URI groups expand into a flat
list of member URIs, by resolving groups through the IBM® WebSphere XML
Document Management Server Component (IBM XDMS).
- If message capture is enabled by policy, the Message
Interceptor mediation primitive logs the required part of the message
to a database. If address tracking is enabled by policy, the mediation
primitive compares the addresses specified by the policy with the
target addresses in the message. If a match is found, the target addresses
are logged to the database with the corresponding message.
- If the SLA Enforcement mediation primitive
is enabled, then monitoring information is adjusted and the statistics
information is checked to ensure that a request can be processed.
- The backend Web service is invoked.
- If enabled for the particular service operation, response statistics
are recorded.
- The filter step checks whether message capture is enabled
by policy. If so, the message is logged to a database using the mediation
primitive provided by WebSphere ESB.
- The Message Element Remover mediation primitive checks the user
principal against the requester exception list. If the requester is
not in the list, and if TWSS headers exist, the Message Element Remover
removes the TWSS headers element, using an appropriate XPath selector.
Upon completion of the flow, the response object is returned through
the SCA export invocation, as the Web service response. If a failure
occurs during the execution of the request portion of the flow, then
fault handling segment of the flow is invoked. See the topic Access
Gateway fault flow for details.