Report prepared for the Experts Meeting Towards the Implementation of a Global Invasive Species
Information Network (GISIN), 6-8 April, 2004. Baltimore, Maryland, USA.
Page 40
8/30/2004
The envelope language is SOAP. There is
also something called the protocol
language. In the case of Web Services this
protocol language is the Web Services
Description Language (WSDL), which
addresses processes that are not about the
envelope or the content of the envelope, but
rather the many behind-the-scenes things
that occur in the system.
The WSDL is also able to perform the query
function – although it need not express what
kinds of queries can be made to a Web
Services server. This is one of the ways in
which Web Services is slightly more
powerful than DiGIR. DiGIR is designed to
have queries expressed in a specific way (a
small extension of Structured Query
Language (SQL)). That characteristic
simplified the design of DiGIR substantially.
Working with this framework does not
involve much work on the part of the
information manager.
If you wish, you might think of it as the post
office. There’s a system called Axis
(developed by Apache) that manages the
post office. One interesting thing about Axis
is that the hard work that must be performed
by people deploying a Web Service is
neither more nor less than the same hard
work that must be done if you’re using some
other mechanism to allow access to your
databases. The components on the server
side are literally the same as what we call
middle-ware, which you would use for any
other mechanism so there is not much more
work involved. On the client side, there is
something called Web Services and
Location Framework that has a similar
ability.
…there is a very large base of
existing software support for Web
Services and they are easy to install.
Why should anyone be interested in Web
Services? Firstly there is a very large base
of existing software support for Web
Services and they are easy to install.
Another very important characteristic of
Web Services is that they are agnostic with
respect to how the information moves. Web
Services are not restricted to HyperText
Transfer Protocol (HTTP), which is used
with browsers. In fact information can even
be transported by email.
Accommodating users that do not have
permanent connections to the Internet is
among the limitations to information
exchange being discussed during this
meeting. An application based on Web
Services infrastructure can be developed to
look the same to users without permanent
Internet connectivity as it does to those with
high speed permanent Internet connectivity
except that behind the scenes, an email is
sent to the Web Services server and then
the answer is returned in the same way.
The answer may arrive two days later,
rather than 90 seconds later, but there is no
difference in the delivery process. Queries
could even be made to a compact disc on
your own machine.
How
•
Envelope language is SOAP
•
Protocol language is WSDL
–
(analogy: how mail is sorted and delivered based on the
envelope and other things independent of the content)
–
WSDL expresses what kinds of queries can be made to the
server, where and how to ask and how the content will be
returned.
•
Content is typically, but not necessarily XML
•
Little work for maintainers:
–
Server side: Apache Axis handles all envelope
construction, management and delivery of query to
middleware, which can be identical to the middleware
required for non WS solutions, such as server side support
for CGI, JSP, or Javascript.
–
Client side, Apache Web Services Invocation Framework
manages all extraction of content from envelope and
delivery to the application
 |
 |
 |