SOCRADES: A Web Service Based Shop Floor Integration Infrastructure
Abstract: In this paper the author presents the SOCRADES middleware for business integration; an architecture focused on coupling web service enabled devices with enterprise applications. First of all,the author elaborated and structured a set of requirements for the integration problem and then proposed a concrete architecture containing components which realize the required functionality of the system. Finally, the author give a reference implementation of the SOCRADES architecture.
Main Concepts:
- device-level services: Comparing with enterprise application and services, device-level services are much more granular, exhibit a lower reliability(especially if they are connected wirelessly) and higher dynamicity and are more focused on technical issues than on business aspects.
- enterprise application and services
System Requirements for this approaches:
1.Functional Requirements:
- Web Service based direct access to devices: Back end services must be able to discover and directly communicate with devices, and consume the services they offer. This implies device should use a publish-subscribe event notifications mechanism.
- Web Service based direct access to back end services: Device service can access Back end services . This make devices can make decisions based on its local information and information from back end system.
- Service Discovery: there should be a automatic service discovery mechanism.
- Brokered access to events: devices' online status often change(including the service they host), so buffered service invocation should be in-place.
- Service life cycle management: need a open ways of managing device service's life cycle.
- Legacy device integration:need to implement gateways and service mediators to allow integration of the non-web service enabled devices(Devices of older generations)
- Middleware historian: need to logging of data, events and the history of devices .( especially analysis of up-to-now behavior of devices and services is needed.)
- Middleware device management: require approaches that will effectively enable the full integration of device data and their exploitation above the device-level.
2.Non-Functional Requirements:
- Security Support: confidentiality, integrity , availability must be tackled. In a web service mash-up, devices must be able to authenticate themselves to external services and authenticate/control access to services they offer.
- Semantic support: facilitates the basic blocks primarily for service composition and meaningful data understanding and integration. Support for the usage of ontologies and semantic-web concepts will also enhance collaboration as a formal description of concepts, terms, and relationships within a manufacturing knowledge domain.
- Service Composition: the architecture should support compose services:1) at device level 2) at back end level and 3) in bidirectional cross-level way.
The Proposed Architecture:
According to the author, the proposed architecture realizes requirements above through components, each one offering a unique functionality.
And the author present a concrete integration architecture focusing on leveraging the benefits of existing technologies and taking them to a next level of integration through the use of DPWS and the SOCRADES middleware.
The architecture proposed is composed of four main layers:
- Device layer: is composed of device.
- SOCRADES middleware: just use functionality of xMII as a basis and extend it. And it include two parts: device service and Application service.
- SAP xMII: the author leveraged and extended the xMII to provide an even richer integration platform.
- Enterprise Application
Then the author give the features and components of the SOCRADES Middleware:
- Brokered Access to Devices
- Service Discovery: carries out service discovery on device level.
- Device Supervision: The device manager holds any static device data of all on-line and off-line devices. The device monitor contains information about the current state of each device. And the middleware historian can be configured to log any event occurring at middleware level for later diagnosis and analysis.
- Service life Cycle Management: manage the service running on device.
- Cross-layer service catalogue: realizing service composition at middleware layer(enrich device service with business context-ontology and these can be used for semantic discovery of services and for assistance in modelling and verifying processes based on them), and allows DPWS devices to discover and use enterprise service.
- Security support: use an role-based access control of devices and message integrity and confidentiality is provided by the WS-Security.