SOA and User Interfaces (UI) part of Industrial SOA series

Overcoming the challenges to developing user interfaces in a service oriented architecture.

Part of the Industrial SOA article series

Abstract: The interaction between user-interfaces and services in an Service Oriented Architecture is an often-neglected topic. This article focuses on the particular challenges that need to be overcome when creating user-interfaces while entire process chains have to be called and interacted with. After outlining some general architectural considerations, the authors describe a practical application of Thomas Erl's UI Mediator pattern that will be accompanied by their own technical experience.


In the simplest scenario, a user's interaction with a business process consists of initiating the process and awaiting the result. However, processes very rarely run completely automatically, meaning human intervention in a process cycle is an important requirement. The WS-HumanTask specification can fulfill this requirement in the SOA environment. A standardized API that is defined for a workflow service can be used to fill a mailbox with tasks. If the process automation language BPEL is used, the BPEL4People specification defines how this mailbox functionality can be used directly in the process cycle by means of the WS-Human Task. Of course, this is possible from BPMN, too.

For example, if manual approval or the input of additional data is needed during a process cycle, the process can determine the correct actor and deposit the task in their mailbox via the task service. The HumanTask service provides a Web service API for this functionality. The users receive the entries in their mailbox and process the pending tasks sequentially, while the process resumes its work in the background.

Human Interaction & Mailboxes

This solution concept is flawless from a technical viewpoint, but its handling is unfamiliar to many users. Workflows can even be perceived as disruptive for short processes that lack role changes, since conventional data-driven application systems can provide immediate responses without detouring to a mailbox. Process control is embedded in the interface control.

Users are their own process masters when such conventional applications are used, whereas a mailbox-supported solution subjects the users to the restrictions of a prescribed process.

Anyone designing classic BPMN or BPEL processes with mailbox interaction understands that users will be faced with a long list of tasks in their mailbox, which often require mechanical and repetitive interactions. Nowadays, many technical departments are aware of this issue, and provide assistance to the users whose daily processes need their requirements recorded.

With the advent of SOA and loose coupling, work processes are further automated and process control is gradually shifted to the back-end. Excessively close coupling of processes and interfaces should be avoided, since processes can also be subject to frequent adaptations due to flexibility. Decoupling via the mailbox is generally the most effective solution.

Read the full article in the Service Technology Magazine or at OTN.

Share your comments and feedback on the Industrial SOA series by using the hashtag #industrialsoa.

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