Taking Care – Error Handling - Applied SOA Patterns on the Oracle Platform - page 489

Error-handling design rules
Common requirements combined with discovered EH handling properties are expressed in
the following points. By combining them together, we will strive to deliver fault-handling
solutions for the entire SOA infrastructure, where composition controller(s) are the corner-
stone. A single component's exception handling (only on BPEL or OSB) is not enough for
enterprise-wide implementation, as it will lead to fault misses and mishandling of security
threats:
• Rule 1 : Error Handling Centralization on SB. EH Centralization will be main-
tained for agnostic Service Brokers ( SBs ) that broker service calls between het-
erogeneous components. Primarily, it must unify the OSB and SCA fault-handling
frameworks, allowing error recognition (listening), catching, and propagation of
unified policy-based handlers. Two handlers will be maintained for sync and async
errors' resolution. This maintenance denotes reuse, as we have already demon-
strated two types of Service Brokers that are capable of handling happy and un-
happy tasks. Processing centralization will be based on three other Centralizations
(Policy, Logic, and Metadata).
• Rule 2 : Extend Metadata Centralization on Logs. Centralization must be applied
to the metadata (service and fault object/message), policies, and logs. The immedi-
ate result of this centralization is the decreasing of fault message Model/Format
Transformations between fault frameworks and fault handlers (logging MDBs,
for instance). The main goal is to present ESR with all the metadata elements cent-
ralized. The MDS is an adequate option for SCA's metadata and policies.
• Rule 3 : Contemplate the delegation of primitive recovery actions to service edges.
Metadata Centralization after analysis, similar to the one offered previously in the
Maintaining Exception Discoverability section, will present the list of common
faults and primitive recovery actions ( Retry , Abort , and Continue ) that can
be immediately delegated to service edges (OSB and ABCS, the first line of EH
handling) and provide ways of fault elevation/propagation back to SB (second
line). Common faults should include the standard faults defined in the WS-BPEL
specification (20 generic faults; see the BPEL 2.0 documentation). Redundancy
with your own custom code will be avoided (don't reinvent the wheel, just discover
and abstract).
• Rule 4 : Balance the Policy Centralization on the platform/frameworks. Policy
Centralization will be applied to a meaningful extent. This means that by being
realistic, we can hardly present some kind of universal policy (as one XML file),
suitable for all OFM elements and frameworks. For instance, in SCA, we have