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Web Services, has been to coopt the Web protocol, HTTP, as a transport layer
because of its ability to pass through most firewalls. This use of HTTP is
convenient but also creates potential security problems as HTTP traffic is
no longer just innocuously fetching Web pages. Instead, it may be making
direct calls on internal applications.
WS-Security and its associated standards address these problems by
providing strong cryptographic mechanisms to identify callers (authenti-
cation), protect content from eavesdroppers (encryption), and ensure infor-
mation integrity (digital signatures). These standards are designed to be
extensible, letting them be adapted easily to new security technologies and
algorithms, and also supporting integration with legacy security technolo-
gies. WS-Security supports intermediary-based application architectures by
allowing multiple security header elements, each labeled with the role of
their intended recipient along the processing chain, and by supporting par-
tial encryption and partial signatures. For instance, the sensitive credit card
details can be hidden by encrypting them while leaving the rest of the mes-
sage unencrypted so that it can be read by the routing application.
The final set of Web Service standards supports transactions and reli-
able messaging. There are two types of Web Service transactions supported
by standards. WS-AtomicTransactions supports conventional distributed
ACID transactions and assumes levels of trust and fast response times
that make this standard suitable only for internal application integration
tasks and unusable for Internet-scale application integration purposes.
WS-BusinessActivity is a framework and a set of protocol elements for
coordinating the termination of loosely coupled integrated applications.
It provides some support for atomicity by invoking compensators when a
distributed application finishes in failure.
The support for reliable messaging in Web Services simply ensures that
all messages sent between two applications actually arrive at their destina-
tion in the order they were sent. WS-ReliableMessaging does not guarantee
delivery in the case of failure, unlike queued messaging middleware using
persistent queues. However, it is still a useful standard as it provides at most
once in-order message delivery over any transport layer, even unreliable
ones such as UDP or SMTP.
8.7 Semantic Web Services
Semantic Web Services (SWS) were proposed in order to pursue the vision
of the Semantic Web presented in, whereby intelligent agents would be
able to exploit semantic descriptions in order to carry out complex tasks on
behalf of humans. Semantic Web Services were first proposed as an exten-
sion of Web Services with semantic descriptions in order to provide formal
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