Matthias Wieland

Towards Reference Passing in Web Service and Workflow-Based Applications

In a Service-Oriented Architecture (SOA) based on Web Service technology the services typically communicate with each other by passing data values directly from one service to another. In the case the services are orchestrated by workflows the services receive their input values from the workflow engine and return their calculated results back to the engine by value. In this paper we show several use cases where such value passing behavior has drawbacks. To address this challenge we introduce the concept of pointers in SOA. Pointers allow services to pass their data by reference which is a fundamental advantage for Web Service communication. Furthermore we show an extension of BPEL that introduces reference variables as new type of data containers in workflows. In addition, for the management of pointers we present the Reference Resolution System which can be used in very flexible setups either as central or distributed system.

Adding High-level Reasoning to Efficient Low-level Context Management: A Hybrid Approach

Rule-based context reasoning is an expressive way to define situations, which are crucial for the implementation of many context-aware applications. Along the scenario of the Conference Guard application we show how this reasoning can be done both by leveraging an efficient context management (realized by the Nexus platform) and by a generic rule based service. We present the architecture of the Nexus semantic service, which uses the underlying definition of a low-level context model (the Nexus Augmented World Model) to carry out rules given in first order logic. We realize this service in a straight forward manner by using state-of-the-art software components (the Jena 2 framework [1]) and evaluate the number of instances this approach can handle. Our first experiences show that a pre-selection of instances is necessary if the semantic service should work on a large-scale context model.

SOEDA: A Method for Specification and Implementation of Applications on a Service-Oriented Event-Driven Architecture

Both Event-Driven Architecture (EDA) and Service- Oriented Architecture (SOA) are unique architectural styles widely used in today’s industries. However, they mostly exist as isolated systems that could greatly benefit from each other when being combined. This paper introduces SOEDA, an approach that unifies EDA and SOA by introducing a development method taking advantage of the unique properties of each architecture. The different steps of the method reach from abstract process specification over event and process implementation to the the final execution phase – described in an abstract manner and by means of an example. Resulting applications are based on state-of-the-art workflow technology using events to trigger the execution of individual business activities.

Making the World Wide Space happen: New challenges for the Nexus context platform

Context-aware applications rely on models of the physical world. Within the Nexus project, we envision a World Wide Space which provides the conceptual and technological framework for integrating and sharing such context models in an open, global platform of context providers. In our ongoing research we tackle important challenges in such a platform including distributed processing of streamed context data, situation recognition by distributed reasoning, efficient management of context data histories, and quality of context information. In this paper we discuss our approach to cope with these challenges and present an extended Nexus architecture.

Policy4TOSCA: A Policy-Aware Cloud Service Provisioning Approach to Enable Secure Cloud Computing

With the growing adoption of Cloud Computing, automated deployment and provisioning systems for Cloud applications are becoming more prevalent. They help to reduce the onboarding costs for new customers as well as the financial impact of managing Cloud Services by automating these previously manual tasks. With the widespread use of such systems, the adoption of a common standard for describing Cloud applications will provide a crucial advantage by enabling reusable and portable applications. TOSCA, a newly published standard by OASIS with broad industry participation provides this opportunity. Besides the technical requirements of running and managing applications in the cloud, non-functional requirements, like cost, security, and environmental issues, are of special importance when moving towards the automated provisioning and management of Cloud applications. In this paper we demonstrate how non-functional requirements are defined in TOSCA using policies. We propose a mechanism for automatic processing of these formal policy definitions in a TOSCA runtime environment that we have developed based on the proposed architecture of the TOSCA primer. In order to evaluate our approach, we present prototypical implementations of security policies for encrypting databases and for limiting the geographical location of the Cloud servers. We demonstrate how our runtime environment is ensuring these policies and show how they affect the deployment of the application.

Virtualizing Services and Resources with ProBus: The WS-Policy-Aware Service and Resource Bus

A fundamental principle of service oriented architectures is the decoupling of service requesters and service providers to enable late binding of services at deployment time or even dynamic binding of services at runtime.This is important in enterprise settings, where different services that implement business functions in critical business processes are dynamically chosen based on availability or price. The same problem also applies to dynamic Grid environments where resources need to be dynamically chosen based on availability and other non-functional properties. The WS-Policy framework describes how policies for both providers and requesters are specified to allow the selection of services based on these policies. Existing approaches, using WS-Policy,have drawbacks by placing the burden of the service selection partially on the client. In this paper we present an extended enterprise service bus that allows service clients to submit policies to which service providers need to comply with together in one message with the service invocation request. We show how these policies are evaluated in the bus and how policies are defined for not only stateless services, but also stateful resources.

Managing Technical Processes Using Smart Workflows

Technical processes that are crossing the boundary to the physical world can be found in many application domains, like logistics or in Smart Factory environments. We show how these processes can be realized by so-called Smart Workflows. To integrate external information sources like context provisioning services, we introduce the Integration Process architecture pattern. This pattern generally solves the problem of integrating different complex systems that provide functional similar services with non-fitting interfaces into workflows. The pattern allows that workflows use simple domain specific interfaces that are the same for any of these systems and by that allow the exchange of underlying systems without changing the workflows. This is accomplished by reducing the interface complexity of the systems via a hierarchical Web Service stack that reaches from the lowest technical granularity needed by IT experts to the domain specific granularity needed by the domain experts. Furthermore the paper presents a concrete realization of the pattern for integrating different context provisioning systems into workflows.

Tool support for the design and management of context models

A central task in the development of context-aware applications is the modeling and management of complex context information. In this paper, we present the NexusEditor, which can ease this task by providing a graphical user interface to design schemas for spatial and technical context models, interactively create queries, send them to a server and visualize the results. One main contribution is to show how schema awareness can improve such a tool: The NexusEditor dynamically parses the underlying data model and provides additional syntactic checks, semantic checks, and short-cuts based on the schema information. Furthermore, the tool helps to design new schema definitions based on the existing ones, which is crucial for an iterative and user-centric development of context-aware applications. Finally, it provides interfaces to existing information spaces and visualization tools for spatial data like GoogleEarth.

PerFlows for the computers of the 21st century

In 1995, Mark Weiser introduced a scenario about the future life, where everyday objects are equipped with smart functions and the environment helps us to fulfill our everyday tasks. This paper shows how Weisers scenario can be realized by todays available technologies. We combine PerFlows (to model the flow of daily tasks) and the Nexus context provisioning platform (to model and provide necessary context information to applications and devices). Furthermore, we present SmartGPS, which is able to provide fused location information even if the device is disconnected.

Towards situation-aware adaptive workflows: SitOPT — A general purpose situation-aware workflow management system

Workflows are an established IT concept to achieve business goals in a reliable and robust manner. However, the dynamic nature of modern information systems, the upcoming Industry 4.0, and the Internet of Things increase the complexity of modeling robust workflows significantly as various kinds of situations, such as the failure of a production system, have to be considered explicitly. Consequently, modeling workflows in a situation-aware manner is a complex challenge that quickly results in big unmanageable workflow models. To overcome these issues, we present an approach that allows workflows to become situation-aware to automatically adapt their behavior according to the situation they are in. The approach is based on aggregated context information, which has been an important research topic in the last decade to capture information about an environment. We introduce a system that derives high-level situations from lower-level context and sensor information. A situation can be used by different situation-aware workflows to adapt to the current situation in their execution environment. SitOPT enables the detection of situations using different situation-recognition systems, exchange of information about detected situations, optimization of the situation-recognition, and runtime adaption and optimization of situation-aware workflows based on the recognized situations.