Axis2 is an effort to re-design and totally re-implement both
Axis/Java and (eventually) Axis/C++ on a new architecture.
Evolving from the now standard "handler chain" model which
Axis1 pioneered, Axis2 is developing a more flexible pipeline
architecture which can yet be managed and packaged in a more
organized manner. This new design acknowledges the maturing
of the Web services space in terms of new protocols such as
WS-ReliableMessaging, WS-Security and WS-Addressing that are
built on top of the base SOAP system. At the time Axis1 was
designed, while it was fully expected that other protocols
such as WS-ReliableMessaging would be built on top of it,
there was not a proper extension architecture defined to
enable clean composition of such layers. Thus, one of the
key motivations for Axis2 is to provide a clean and simple
environment for like Apache Sandesha and Apache WSS4J to
layer on top of the base SOAP system. Another driving force
for Axis2 as well as the move away from RPC oriented Web
services towards more document-oriented, message style
asynchronous service interactions. The Axis2 project is
centered on a new representation for SOAP messages called
AXIOM (AXIs Object Model). AXIOM consists of two parts: a
complete XML Infoset representation and a SOAP Infoset
representation on top of that. The XML Infoset representa-
tion provides a JDOM-like simple API but is built on a
deferred model via a StAX-based (Streaming API for XML)
pull parsing API. A key feature of AXIOM is that it allows
one to stop building the XML tree and just access the pull
stream directly; thus enabling both maximum flexibility
and maximum performance. This approach allows us to
support multiple levels of abstraction for consuming and
offering Web services: using plain AXIOM, using generated
code and statically data-bound data types and so on. At
the time of Axis1's design, RPC-style, synchronous,
request-response interactions were the order of the day
for Web services. Today service interactions are much more
message-oriented and exploit many different message exchange
patterns. The Axis2 engine architecture is careful to not
build in any assumptions of request-response patterns to
ensure that it can be used easily to support arbitrary
message exchange patterns.

• Igor Vlasenko

• axis2