What is the motivation?

Dynamic reconfiguration is highly demanded in long-time running systems where a break of services is not tolerable, as well as in mobile systems where services have to be dynamically adapted to meet the varying client environments. Many approaches have been proposed to address the dynamic reconfiguration of component software systems. However, the existing approaches follow a strategy of waiting until safe state, which may collaps in an extreme case where the affected components are involved in long-time interactions or processing.

In addition, for enterprise applications, especially mobile applications, providing personalized services is a greate feature to attract customers. In order to provide personalized services, software systems have to support multiple solutions synchronously.

Routing Based Workflow - Temporary Binding

The team of Prof. Dr. Christoph Meinel proposed a technology named Routing Based Workflow (RBW) to model the execution and management of collaborative components. In RBW, an XML based configuration language was designed to specify the properties and IO behaviors of each component and the interactions among different components. More importantly, through modeling the execution environment of collaborative components, a highly flexible execution management of components is achieved. In RBW, the execution of components is separated into two phases: virtual binding and real binding. The virtual binding creates an idle execution environment for components, on which the reconfiguration operations can be immediately carried out. The real binding is triggered by the arrival of requests to guide the executions of series of components. The separation of the execution procedure realizes temporary binding for component instances. The temporary binding means the component instances are only temporarily loaded into a created execution environment to execute their functions, and then, released to their repository after executions. In RBW, the execution environment can be changed and duplicated. By supplying multiple execution environments synchronously, the RBW is able to support multiple solutions for components collaboration, which can be employed to develop systems providing personlized services.

Fig.1. Working Diagram of Routing Based Workflow

SDS3 - A Dynamic, Secure Middleware System

Based on the technology of RBW and CORBA, we developed a dynamic and secure middleware system - the Smart Data Server Version 3.0 (SDS3). Instead of as middleware services, here security is integrated into core components of middleware system, which are managed by RBW and are possible to be dynamically reconfigured to adapt the changes of environment. In the design and implementation of SDS3, an open source project openORB, a java implementation of CORBA, has been adopted and modified as the communication infrastructure. The Object Request Broker (ORB) takes charge of the responsibility of transferring the request and response over Internet. RBW takes the similar role as DSI to manage the secure components to make secure invocation. To integrate RBW with CORBA smoothly, parts of CORBA are modified. In the client side, a wrapper package for Dynamic Invocation Interface (DII) was created to enable directly creating object references for remote targets and carrying routing information. In the server side, a workflow adapter was created to take the role of Basic Object Adapter (BOA) or Portable Object Adapter (POA), and registered as the object adapter for all deployed applications. The secure components work in the model of Role Based Access Control (RBAC) to enhance the security of invocation. Brief descriptions of three secure components are given as follows:

Authenticator adopts the technology of Public Key Infrastructure (PKI) and offers two functions: authentication and non-repudiation.

Authorizer is responsible for extracting and confirming the roles of user according to authenticated information. Attribute Certificate (AC) is applied here to maintain one or more privilege attributes of users.

Access Controller makes the decision for permission giving on the basis of authorization policy and received roles of the current user.

Fig.2. Architecture of Smart Data Server Version 3.0

Features:

• Provide multi-levels security control from security strategy-control to policy based detail-control for specific applications.
• Applications are pure business logics that does not contain any security source codes.
• Security strategy-control can be dynamically changed, which is a feature inherited from RBW.
• Synchronously support multiple security strategy-control solutions for different sensitive applications.

DSC - A System for Services Dynamic Composition

We also applied the technology of Routing Based Workflow (RBW) to our web services composition system - the Dynamic Services Composer (DSC), where service activity models a business service and acts as a component node of RBW. In DSC, we employed two open source project, Apache Axis which composes the foundation platform to publish web composite services, and Apache Web Service Invocation Framework (WSIF) which helps to construct service invoker. Unlike the current approaches of web services composition where only service provider can be dynamically determined, DSC achieve the dynamic capability not only for service providers binding and also for flow structure of composition services.

Fig.3. Architecture of Dynamic Services Composer

Research Members

• Dipl. Inform. Wanjun Huang
• Prof. Dr. Christoph Meinel
• Dipl. Inform. Uwe Roth (Former)
• Prof. Dr. Ernst-Georg Haffner (Former)
• Prof. Dr. Thomas Engel (Former)

Related Publications

• Conference Papers

Resource Links

• Related Research Groups:
  Distributed Multimedia Reseach Group, Lancaster University
  Distributed Systems Reseach Grup, University of Newcaslte upon Tyne
  Distributed Systems Research Group, Universidade de São Paulo
  Open System Laboratory, University of Illinois at Urbana-Chamaign

• More Resource Links:
  IEEE Distributed Systems Online: Middleware
  Reflective Middleware Resource Page

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