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DigiCULT
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Info
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Services vision to become a cross-
platform, product-independent reality.
SOAP, the Simple Object Access
Protocol
11
, is a lightweight communica-
tions protocol, used to transfer Web
Service requests, responses and results
between one system and another. To
quote the current specification, `it is an
XML based protocol that consists of
three parts: an envelope that defines a
framework for describing what is in a
message and how to process it, a set of
encoding rules for expressing instances of
application-defined data types, and a
convention for representing remote pro-
cedure calls and responses.'
WSDL, the Web Services Description
Language
12
, describes the services them-
selves, telling other systems how to
communicate with them, and what sorts
of operations they are capable of under-
taking.
UDDI, Universal Description,
Discovery and Integration (of Web
Services)
13
, is a protocol for building
directories of Web Services.You (or a
machine acting on your behalf) might
search a UDDI directory in order to
select the most appropriate currency
conversion Web Service to integrate with
your own application, for example.
These four are normally seen as the
basic building blocks for any Web
Services implementation. On their own,
they are not sufficient to allow con-
struction of the rich and flexible services
that there is interest in creating, and
there is a growing set of related standards
that will sit on top of this core. Of these,
three are worth mentioning here.
WSFL, the Web Services Flow
Language
14
, describes the manner in
which data and interactions pass from
one Web Service to another, and will be
fundamental for those who seek to build
to translate the
content of each metadata element separa-
tely.
Figure 2 DC-dot looking at the English-
language metadata for the UKOLN homepage
Figure 3 DC-dot, having translated the
UKOLN homepage's metadata into German
TASTING ACRONYM SOUP
Web Services are not delivered by a
single, all encompassing, new standard.
Rather, they are an enabling technology,
building upon existing systems and
processes in a predictable and standards
or specification conformant fashion.
XML, eXtensible Markup Language
10
,
is the glue underlying the whole Web
Services approach. Much of the content
is marked up, or tagged, as XML, and
many of the more complex aspects of the
Web Services approach, below, are
expressed in XML. The evolution and
increasingly widespread adoption of
XML makes it possible for the Web
10http://www.w3.org/XML/
11http://www.w3.org/TR/SOAP
12http://www.w3.org/TR/wsdl
13http://www.uddi.org
14http://www-4.ibm.com/software/solutions/
webservices/pdf/WSFL.pdf
15http://www.oasis-open.org/committees/wsrp
16http://www.oasis-open.org/committees/wsia/
complex aggregations of Services into a
single application.
WSRP/ WSIA, Web Services for
Remote Portals /Web Services for
Interactive Applications
15,16
. Two separate
working groups initially, these two appear
to be coming together in a single specifi-
cation that will describe the manner in
which individual Web Services are made
available for calling from within portals
of various types.
The growing family of related Web
Services specifications is seen, in business
at least, as an important step forward in
enabling a truly interactive, transactional
experience on the Web. Crucially, these
new specifications layer on top of well-
established existing standards and proto-
cols, such as the TCP/IP communica-
tions protocols, meaning that we lose
none of the existing options as we add
these new ones.
How much Web Services offer, directly,
to the cultural heritage sector is an area
for us to explore, but to ignore what is
happening in this area is no longer a
viable option.
ACKNOWLEDGEMENTS
This paper was informed by Ian
Dolphin's internal document on Web
Services for the University of Hull's
Digital University Project (http://digital.
hull.ac.uk/), as well as discussions with