David Paul, Mark Wallis, Frans Henskens and Michael Hannaford
School of Electrical Engineering and Computer Science, University of Newcastle, NSW, Australia
Web Services, transactions, Super Browser, ACID.
In the Web Services environment, traditional ACID transactions are not always sufficient to support the ac-
tivities that businesses would like to process. While Web Services transactions standards do exist, it is still
difficult for an end-user to combine services from loosely-coupled providers into a single action to be per-
formed. We describe the use of a “Super Browser” that enables users to more easily nd and combine Web
applications into a single activity that they can view and manipulate throughout its life-cycle.
In the Web Services environment, traditional ACID
transactions are not always sufficient to support the
activities that businesses would like to process. Trans-
actions that involve multiple service providers can
run for long periods of time. This can result in
negative side-effects when combined with traditional
transaction-based concurrency control mechanisms.
While Web Services transactions standards do exist,
it is still difficult for an end-user to combine services
from loosely-coupled providers so that they are used
as a single action. Additionally, these existing stan-
dards are targeted primarily towards predefined trans-
actions that are static and involve little or no direct
human interaction.
This paper describes the use of a “Super Browser”
that enables users to more easily find and combine
Web applications into a single activity that they can
view and manipulate throughout the activity’s life-
cycle. Initial support will allow the end-user to gener-
ate ad hoc transactions that contain multiple interac-
tive Web application sessions. The design is extend-
able and supports the orchestration of both interactive
and non-interactive Web Services.
The paper is organised as follows: Firstly a brief
review of transactions is given, explaining the ACID
properties and their typical reductions. A Super
Browser design concept is then presented to sup-
port ad hoc transaction creation and orchestration,
with a primary focus on integrating non-Web Service-
based Web applications into a transactional structure.
An outline is given for the support that a non-Web
Service-enabled Web application must provide so it
can participate in transactions managed by the Super
Browser’s transaction manager.
A transaction combines a group of independent ac-
tions into a single action with a set of predictable out-
comes. Traditional transactions, where only a single
system is involved, are well understood (Gray and
Reuter, 1993). There is also a large body of the-
ory (Garcia-Molina and Salem, 1987; Younas et al.,
2000), behind techniques to support transactions in
environments such as that of Web Services. A prob-
lem with these methods, however, is that the transac-
tions are typically not dynamically configurable, es-
pecially with regard to human interaction.
2.1 Multidatabase Transactions
Traditionally, transactions are required to adhere to
the ACID properties of Atomicity (ensuring that all
actions in the transaction either complete success-
fully, or revert to a state where none of them were
run), Consistency (ensuring that the system is not
put into an illegal state), Isolation (letting concur-
rent transactions run as if they were the only transac-
tion being processed), and Durability (ensuring that
any completed transaction has its outcome recorded
Paul D., Wallis M., Henskens F. and Hannaford M. (2008).
In Proceedings of the Fourth International Conference on Web Information Systems and Technologies, pages 269-272
DOI: 10.5220/0001522902690272
on a stable medium and cannot be undone, even by
accidental events such as hardware or software fail-
ure). However, while transaction management in tra-
ditional systems typically offers an acceptable level
of service, the same cannot be said for transactions
achieved by combining services offered by multiple
systems. Such multidatabase transactions often run
for much longer periods of time than traditional trans-
actions, so locking any data may block other transac-
tions for an unacceptable length of time (Little, 2003).
Because of this, the traditional ACID properties are
typically reduced in strength, helping to ensure that
the entire system maintains an acceptable level of ser-
2.1.1 Reduction of Acid Properties
The main problem with Web Services transactions is
that the cost to globally enforce the ACID proper-
ties traditionally needed for transactions is too great.
Thus, there are many proposals to reduce the strength
of some of the properties in these and similar sys-
tems (Garcia-Molina and Salem, 1987; Younas et al.,
2000). Typically, consistency and durability are seen
as required properties, whereas atomicity and isola-
tion are the properties that are weakened.
Atomicity is intended to ensure that either a trans-
action completes successfully or the system is re-
verted to a state as if the transaction never ran. As
the failure of a single transaction can affect the result
of any other transaction that was processed while that
transaction was running, atomicity is considered in-
feasible in the Web Services environment. Typically
strict atomicity is replaced with a weaker version,
most frequently semantic atomicity (Garcia-Molina,
For Web Services transactions, atomicity is also
often further reduced (Little, 2003). Rather than re-
quiring every service provider involved in a transac-
tion to see the same result, it is sometimes useful to
have some providers believe that the transaction has
failed while others believe that it has succeeded. The
main reason for this has to do with the definition of
success. In Web Services transactions, multiple re-
sults may be seen as acceptable, so the failure of a
single service provider may simply lead to a different
acceptable state rather than to outright failure (Little,
The other property typically reduced in strength
for Web Services transactions is isolation. While tra-
ditional optimistic concurrency control has been de-
veloped for Web Services transactions (Choi et al.,
2005; Haller et al., 2005), and this completely sup-
ports isolation in the traditional sense, these tech-
niques do nothing to solve the problem of the reduc-
tion of service levels that the strict support of isolation
seems to demand. In fact, in order to keep accept-
able levels of service, global isolation in Web Services
transactions is typically completely ignored, instead
relying on the local isolation of individual service
providers to avoid most of the problems that a com-
plete lack of isolation would cause. While this does
improve performance of the overall system, ignor-
ing isolation does cause some problems (Paul et al.,
2.2 Interactive Web Applications and
Web Services Transactions
As there are already three well-known standards for
Web Services transactions (Ceponkus et al., 2002;
Cox et al., 2004; Bunting et al., 2003), it may seem
that there is little need for any further standards de-
velopment. However, some processes require inter-
actions unsupported by these standards. This is es-
pecially true when a user needs to interact with the
transaction. The main problem is that Web Services
are mainly seen to be for machine-to-machine inter-
actions, when in many cases human interaction is ei-
ther needed, or desired, to ensure correct results (den
Haan, 2007).
While it is possible for individual Web Services to
require or rely on user interaction, there is currently
no easy way for a user to specify a transaction, other
than writing a program specifically for that transac-
tion. Currently, to combine Web Services offered by
different providers, an end user must either write their
own program (or process model) or use each service
individually (eg through Web interfaces provided for
each service). In the former case, the end user re-
quires too much knowledge of Web Services to make
this acceptable for people outside of the field. In the
latter case, no transactional support is possible. The
following section describes how a Super Browser sup-
ports abstraction over these difficulties to let end users
easily and successfully combine multiple Web appli-
cations into a single transactional unit.
A Super Browser (Henskens, 2007) is a next-
generation Web browser that in addition to standard
Web browser functions, provides a consistent inter-
face for applications to interact directly over the Inter-
net. The Super Browser enables the user to find and
combine services, run ad hoc transactions made up of
these combined services, and manage the transactions
currently being run by the Super Browser.
WEBIST 2008 - International Conference on Web Information Systems and Technologies
The remainder of this paper focuses on the cre-
ation of the Transaction Management facility within
the Super Browser, and the establishment of ad hoc
3.1 Ad Hoc Transaction Creation and
The Super Browser provides a method for users to
create a new ad hoc transaction. This ad hoc trans-
action later has particular Web Services associated
with it manually by the user. The creation function
requests that the user specify a descriptive name for
the transaction. For example, the user may create a
new transaction named the Summer Holiday Book-
ing” transaction that tracks the various Web Services
involved in the organisation of holiday travel.
When the user creates a new ad hoc transaction,
the Super Browser establishes the various data struc-
tures needed to track the progress of the transaction.
The user then has access to a Transaction Viewer page
that lists all the transactions that are currently pending
within the Super Browser.
3.2 Identifying Transaction-enabled
Web Applications
Typically, an interactive Web application does not al-
low a user to interact directly with any internal trans-
actions that take place. For an interactive Web ap-
plication to take part in a transaction managed by the
Super Browser, an extension is provided to support
three basic Web Service calls: establishInteraction(),
interactionStatus(), and rollback().
These three Web Service calls are exposed to the
Super Browser using the existing WSDL (Christensen
et al., 2001) and SOAP (Gudgin et al., 2007) stan-
If a Web application is extended to support these
functions then it needs to notify the Super Browser
that it is able to take part in a managed transaction.
It does this by inserting a specific META tag into
the head of the HTML provided by the Web appli-
cation. The “LINK alternate” META tag described in
the HTML 4.0 specification is used for this function.
RSS feeds (RSS Advisory Board, 2007) currently use
this same functionality for informing a standard Web
browser that the Web application supports the RSS
3.3 Adding a Service to an Existing
When the user requests to add a specific service to
an existing transaction, the transaction manager in
the Super Browser executes the establishInteraction()
Web Service provided by the Web application. This
function is passed the name of the specific service re-
quested by the user. When the Web application re-
ceives this request, it establishes a Web session for
that particular service, and passes back a unique Ses-
sion ID and the URL which can begin this interaction
to the Super Browser.
The Super Browser then takes this information
and creates a new Web browser window. Within this
window the browser automatically navigates the user
to the provided URL and returns the Session ID to
the Web application. This connects the user with the
interactive Web application under the context of the
From here, the user can interact with the Web ap-
plication as if it were not part of a transaction. When
the user has finished using the service (e.g., when they
have finished making their booking), the user or Web
application closes the Web browser window. This
window close action prompts the Super Browser to
call the interactionStatus() function on the Web appli-
cation, passing in the related Session ID. This func-
tion tells the transaction manager if the interactive
session was successful, and whether it should mark
that component of the transaction as complete.
At this stage, the user’s interaction with the Web
application is complete. Since the Web application
is not truly transaction-aware, it has already commit-
ted the result of the user’s interaction to its internal
databases. For example, if the Web application in
question was an Airline Booking service then at this
stage the flight has been booked and the user has been
3.4 Cancelling a Transaction
As the user continues to add various Web Services to
a transaction, a point may be reached where the user
is unable, or unwilling, to continue and wishes to ei-
ther roll back part of the transaction or the transac-
tion as a whole. This is made possible through use of
the rollback() function. This rollback() function takes
the Session ID described above as a parameter and
reverses any internal commits that have already been
performed. In the Airline example from above, this
means that the rollback() function reverses the airline
booking and refunds any payments back to the user,
less any required compensation.
3.5 Commiting a Transaction
Finally, the Super Browser also allows the user to
commit the transaction as a whole. Since each com-
ponent Web Service is not transaction aware, this
commit basically marks the transaction as completed
and does not allow the user to add any additional Web
Services to the transaction or roll back any of the com-
Many end-user activities are best implemented as
transactions (Gray, 1981). Despite this, it is quite dif-
ficult for an end-user to create and manage Web Ser-
vices transactions. We describe features of work in
progress on a Super Browser that improves this situa-
tion. While the browser provides support for Web Ser-
vices transactions standards, it also allows the ad hoc
use of Web applications in a transaction-based con-
Allowing end-users to generate and manage their
own transactions across multiple Web applications
improves the user’s capability to handle cases where a
particular Web Service is unable to fulfil their request.
Taking the Holiday booking scenario as an example,
it has been shown that allowing the end-user to issue
a roll back across a group of disconnected, heteroge-
neous Web Services provides an efficient way for the
user to cancel services that have already been booked
without having to manually interact with each Web
application in turn.
The presented research is focused on enabling
transaction support incorporating non-Web Service-
based Web applications. The Super Browser concept,
though, is extensible and allows for applications to
be developed that can combine both server-to-server
and user-interactive Web Services into a single trans-
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