Applied Architectures and Styles

1. Applied Architectures and Styles Chapter 11, Part 2 • Service-Oriented Architectures and Web Services • Architectures from Specific Domains • Robotics • Wireless Sensor Networks

2. Service-Oriented Architectures and Web Services • Supports business enterprises on the internet • Independence is fundamental • Conceptually part of the decentralized design space • Significant complexity

3. Service-Oriented Architectures and Web Services • Independent Components • Interface describing what operations they provide • Have their own thread of control • Can be described using WSDL • Web Services Description Language • XML • APIs written in languages such as Java, PHP, Ruby

4. Service-Oriented Architectures and Web Services • Connectors of SOA • Asynchronous Event Notification • Sends structured XML document to service provider • Variety of protocols: HTML, Email, etc. • No obligation for provider to return anything to requestor • Different from remote procedure calls • No object persistence • Absence of programming semantics

5. Service-Oriented Architectures and Web Services • Requires Architecture Description Language • Formality and complete semantics required • Similar to a scripting language • Other Architectural Styles and Concepts • Publish/Subscribe Mechanisms for discover of new services or service providers

6. Service-Oriented Architectures and Web Services • Significant Complexity • Interoperability across platforms • Open, decentralized system • Difficult to change services once announced • Compares to Java and changing a public method • Due to these issues, developers often choose REST instead of SOAP • REST – focuses on the exchange of representations/data • SOAP – focuses on the invocations of functions with arguments • Amazon provides both methods

7. Service-Oriented Architectures and Web Services

8. Architectures from Specific Domains • Robotics • Sense-Plan-Act • Subsumption • Three-Layer • Reuse-Oriented • Wireless Sensor Networks

9. Architectures from Specific Domains • Robotics Examples • Mobile tele-operated systems • Full or partial control of the robot’s systems is handled by a human operator • Industrial automation systems • Autonomous • Environment conforms to robot • Mobile autonomous robots • Autonomous • Navigate varying environments

10. Architectures from Specific Domains • Robotics Challenges • Physical platforms and devices • Unpredictable nature of the environment • Robotic Software Qualities • Robustness • Performance • Reusability • Adaptability

11. Architectures from Specific Domains • Sense-Plan-Act (SPA) • Unidirectional • Sense – Interface with the world • Plan – Behavior • Reconciles actual state with internal model • Internal model repeatedly updated in response to newly acquired sensor information • Objective it to keep the model consistent with actual environmental conditions

12. Architectures from Specific Domains • Sense-Plan-Act (SPA) – Drawbacks • Sensor information must be integrated (known as sensor-fusion) and incorporated into planning models at each step • These operations are very time consuming and typically cannot keep up with environmental changes • Therefore this model does not scale well as robot capabilities and goals expand

13. Architectures from Specific Domains • Subsumption • Inhibition and Suppression • No world model or plan • Independent components, each encapsulating specific behavior or skill • Reactive in nature • Excellent performance • Drawbacks • Lack of coherent architectural plan • Components inserted into data flow depending on task without position necessarily being related to the layer with in which they are located

14. Architectures from Specific Domains • Three-Layer Architecture (3L) • Hybrid of SPA and Subsumption • Three Layers • Reactive • Sequencing • Planning • Challenges • Deciding how to separate functionality into layers • Reconciliation of world and behavior models

15. Architectures from Specific Domains • Reuse-Oriented • Component Reuse • Object Oriented • Middleware Frameworks • Few Frameworks • Player (http://playerstage.sourceforge.net) • Orca (http://orca-robotics.sourceforge.net) • Microsoft Robots Studio (http://msdn.microsoft.com/robotics) • Lego Mindstorms (http://www.mindstorms.lego.com)

16. Architectures from Specific Domains • Wireless Sensor Networks (WSN) • Sensor nets • Monitor the environment • Widely used • Medical systems • Navigation • Industrial automation • Low installation costs • Easy reconfiguration

17. Architectures from Specific Domains • WSN Challenges • Integration with legacy systems, other embedded devices, mobile networks • PDAs, cell phones,etc. • Typical Constraints • Power • Bandwidth • Range • Processing capacity • Falt-tolerance • Availability • Scalability

18. Architectures from Specific Domains • Bosch Research and Technology Center and University of Southern California • Three separate architectural styles to achieve all goals • Peer-to-peer • Publish-subscribe • Service-oriented