Applied Architectures and StylesChapter 11, Part 2

• Service-Oriented Architectures and Web Services

• Architectures from Specific Domains• Robotics• Wireless Sensor Networks

Service-Oriented Architectures and Web Services

Supports business enterprises on the internet

Independence is fundamental

Conceptually part of the decentralized design space

Significant complexity

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

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

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

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

Service-Oriented Architectures and Web Services

Architectures from Specific Domains

Robotics Sense-Plan-Act Subsumption Three-Layer Reuse-Oriented

Wireless Sensor Networks

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

Architectures from Specific Domains

Robotics Challenges Physical platforms and devices Unpredictable nature of the environment

Robotic Software Qualities Robustness Performance Reusability Adaptability

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

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

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

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

Architectures from Specific Domains

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)

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

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

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