Mohammad Alrifai 1 WolfTilo Balke 1 Peter Dolog 2 Wolfgang Nejdl 1 1 ! 2 "# #$ %& " &!$! ’ # ( $ $& (& & ) ( ## ) * ! $ ($ $ *#& $! + $ # # $ & + $ , + $& ! - $ & .# &*$&/ ! 0 ## + ## & $& $ # $ ! 0 & + ##& # + #& (# # &$! - $ $ # & ! # ## $ + # & $& $&#$! 0 $ (# + & # $&#$ # $, $1! Web servicebased business processes are generally composed of invocations to internal business processes outsourced by loosely coupled providers. A key requirement for the success of Web servicebased integration of business applications is to ensure a correct and reliable execution of the composed process with regards to partners’ transactional requirements. Web services technology provides standard interfaces like WSDL and XML SOAP messaging for the integration of enterprise applications, however, do not fully support transactional management yet. Web service providers have to control their local resources and ensure their consistency and integrity. Web service requests are treated by local transaction managers as independent transactions and strict ACID properties are enforced by special error recovery and concurrency control components. In contrast to classical database systems, however, a Web servicebased transaction is generally longrunning and involves some independent services that might need to be synchronized manually. To optimize their throughput (and thus their profits) service providers, therefore, cannot grant locks on their resources for some consumers for long time spans. Hence, strict locking based distributed transaction protocols are difficult to apply in Web service environment. More optimistic transaction models with ( property have been recently adopted for Web service transactions where the intermediate results of previous activities are already made visible to the new consumers, even if they are not yet committed (‘dirty read’). Providers leverage compensation mechanisms to recover from any failures or cancellations of executed operations (see e.g. [9, 15, 17, 18] and [4, 5]). Ensuring the correctness of the execution of concurrent transactions under relaxed isolation is left to the local transaction managers of the service providers. However, conventional scheduling algorithms typically do not take into account the timing characteristics of transaction execution and individual time constraints are ignored when scheduling decisions are made (i.e. which transaction is allowed to commit and which transactions have to be delayed). This often leads to blocking transactions later by earlier transactions that still not committed, though they could already be willing to commit their individual execution. This has a great impact on Web servicebased business transactions as those are usually combined with time constraints. For example, consider a Web servicebased process for arranging a business trip to attend some meeting on a specific day. The time factor in such transactions is very valuable and the initiators of these transactions usually have a deadline for committing these transactions and might not be interested in a successful termination after this deadline. In this paper, we propose a nonblocking scheduling mechanism for enhancing the transaction management of Web services to cope with these limitations. Our approach takes into account the deadline constraints of both the consumers and the providers of Web services while scheduling the execution of a global transaction at every participating site. The proposed solution can be applied in a fully decentralized fashion for open dynamic