Transaction support is vital for reliability of business processes which nowadays can involve dynamically composed services across the Internet. However, no single transaction model is comprehensive enough to accommodate various transactional properties demanded by those processes. Therefore we intend to develop a Business Transaction Framework (BTF) that utilizes existing ingredients in the context of contractual business relations. The proposed BTF has °exibility by using a library containing abstracted transaction models, validity based on formalization and business trustworthiness guaranteed by contractual speci¯cations of transactional qualities.
E-business has moved from the simple automation of business applications to the complex integration and coordination of business processes that belong to di®erent organizations. Business processes have grown to be very intricate to involve miscellaneous activities and resources, and often need to invoke services provided by others. In such an environment, various business relationships need to be regulated, which result in a large amount of contracts along the processes. In addition, the dynamically composed activities usually have complex interrelated dependencies which make exceptions and errors prone to occur during the process execution. Suppose there is a booking process in a travel agency which needs to invoke three Web services, hotel booking, car rental and °ight booking respectively. Besides there are activities like billing, payment check etc. which happen internally. These activities exhibit various transactional semantics and the process in a whole may demand di®erent transactional qualities during execution. For instance, when a customer cancels the booking before payment, the previous completed activities have to be rolled back as if the process has never been initiated. However in case of a cancel after payment, the process probably can not be returned to the exact same state when it started. Therefore the process needs comprehensive and °exible transactional support to guarantee reliability.
To address the above concern, the XTC (eXecution of Transactional Contracted electronic services) project was proposed which aims at laying a generic foundation to the transactional support for processes in service-oriented environment. Within this project, my PhD research focuses on the development of a Business Transaction Framework (BTF) for contract-driven, inter-organizational business processes and in particular, on contractual agreements specifying transactional qualities of those business processes.
The rest of the paper is organized as follows. We describe the research background that motivates our work and review the related work in Sect.2. We introduce the BTF and discuss our research approach in Sect.3. We end this paper in Sect.4 with the summary and the discussion of future work. 2
The challenge of e-business nowadays is to integrate distributed applications
into a corporate process which enables free and secure data-°ow and
control°ow across the organizational boundaries. The former way of tightly coupled
integration like EAI (Enterprize Application Integration) can no longer meet
today's requirements. To loosely couple the applications, one approach is
wrapping them as ready-to-use services. The paradigm of Service-Oriented
Computing (SOC) and its underlying Service-Oriented Architecture (SOA) [
Transaction management in Web services-based SOC paradigm is an
intriguing topic in the research of service composition and management. First
appeared in the mid 1970s to address the multi-user, concurrent-program
concern in databases, transaction management has become a prevalent mechanism
to guarantee reliability to running applications. Earlier work like [7{10] on ACID
transactions and advanced transaction models is more or less database-oriented
thus not suitable for complex business processes. Later on, research (e.g. [
Another ¯eld of our interest is e-contracting, which ensures business
processes with legal liability and cost-e±ciency. To sustain a certain level of process
reliability, we propose to use contracts as service level agreements to specify the
agreed transactional qualities of the whole business process as well as each
component service. For example, we may leverage the WSLA (Web Service Level
Agreement) framework [
Today's business environment, which involves multiple partners, diverse processes and heterogeneous systems, motivates us to develop a BTF with its °exibility by using the ATC (Abstract Transactional Construct) library, validity based on BTF/ATC formalization and business trustworthiness guaranteed by the contractual speci¯cation of Tx-QoS. 3
So far we have elaborated a conceptual framework with an underlying architecture that is shown in Fig.1. The basic idea is to utilize existing transactional models and abstract them into ATCs so that they can be selected and composed on demand. The ATC Editor creates, deletes and modi¯es ATCs through the ATC Library Manager in the de¯nition phase. Fed by a process speci¯cation, the ACBT (Abstract Composite Business Transaction) is created by the ACBT Composer and stored in the ACBT library in the composition phase and leverages ATCs as its building blocks. During the execution phase, the CBTs (Composite Business Transaction) are instantiated from the ACBT by the CBT Creator and consist of TCs(Transaction Constructs) instantiated from ATCs. Each CBT Manager monitors and manages one CBT. At the highest level there is a BTF Manager that coordinates the activities of other function components and manages transactions through all three phases of the process life cycle. x
To ensure a °exible and valid transaction framework, we employ classic and widely adopted transaction models and abstract them to shape the ATC library.
ComPhpaosseition BTF Manager
ACBT Composer ACBT Library Manager AACACBCBT(BTs()Ts()s) Dynamic
Data Component
Execution Phase
CBT Creator CCBBTT CBT MMaMnaanaganegaregrer TTCC(s()s) CCBCBTB(Ts(T)s()s)
BTF Management
Layer Artifact Creation Layer
Artifact Management
Layer
Definition Phase ATC Edidor ATC Library Manager
ATACTA(CTs()Cs()s) NOTATION
Function Component
ComDpaotanent
Manage/Control Report/Register
Communication
For each ATC, we de¯ne a set of parameters, among which some are assigned
in the de¯nition phase to specify its internal structure while the others are
assigned in the composition phase to specify its position in an ACBT. We design
the framework based on the Web services standards and place it on top of the
composition layer. To implement the BTF, we develop a reference architecture
delivering the necessary functionalities by following the rules and techniques
suggested in [
One advantage of the proposed BTF lies in the quality control by means
of contractual agreements between the service providers and consumers. So far
there is no available research on contractual transaction speci¯cations. Besides,
there is no clear de¯nition about what are the measurable transactional
qualities of business processes. As a business process may contain activities exhibiting
di®erent transactional semantics, the supporting transaction framework should
accommodate the required Tx-QoS for each component activity as well as the
whole process °exibly. Again we take the travel booking process of Sect.1 for
example, which includes multiple parties like a customer, a travel agency and
candidate hotels, airlines and car-rental companies. Each company involved in
this process has its own internal automated processes and o®ers business
functions through Web services (here we assume each component activity is
automated and wrapped as a Web service). The whole process can be viewed as a
hybrid transaction consisting of various sub-transactions, each dealing with a
transactional Web service. It is very likely that these component services require
di®erent transactional qualities such as the unconventional payment atomicity
[
Our preliminary design of the conceptual and architectural BTF/ATC described in Sect.3 is the ¯rst step towards a comprehensive and °exible transaction framework for contract-driven, service-oriented business processes. The idea is to extract and group existing transaction models into an ATC library and pick up the needed ones to compose a transaction hierarchy on demand. The design work is far from complete, with several directions for the future elaboration:
The ¯rst direction is to achieve a complete and sound BTF/ATC speci¯cation. To guarantee the correctness of the proposed BTF, we need to develop a method to extract and connect ATCs into an ACBT. One approach is to encapsulate the transactional semantics with parameterizable interfaces based on an ATC taxonomy. This way an ACBT can be composed through these interfaces by prede¯ned composition rules.
Secondly, a re¯ned architecture with a complete set of components delivering proper functionalities is required as the blueprint to implement a prototype system. Bearing the unique features (e.g. °exibility, extensibility, compatibility) of the BTF in mind, we plan to decompose some of the function components shown in Fig.1 to get a deeper level of architectural overview. For example, the BTF manager can be decomposed into a second-level architecture that may contain a messenger, a contractor and a monitor and the contractor can be further re¯ned if needed.
Last but not least, we are going to develop a Tx-QoS speci¯cation language. To achieve this, we need to investigate the existing e-contracting languages. In addition, a clear description of intended QoS for transactions is needed. Afterwards we expect to combine the contractual Tx-QoS with the BTF speci¯cation.
The XTC project is funded by the Dutch Organization for Scienti¯c Research (NWO No. 612.063.305). Thanks go to Paul Grefen, Benedikt Kratz and Jochem Vonk whom I work with in this project.