CS486: Tutorial on SOC, OSGi, and Knopflerfish

Ryan Babbitt (rbabbitt@iastate.edu)

(props to Dr. Hen-I Yang, CS415X)

Feb. 3, 2011

Basic Concepts

• Service-oriented computing (SOC)

• Service-oriented architectures (SOA)

– OSGi and Web Services

• Knopflerfish – OSGi implementation in SHL

Services in the Real World

• Specialization is a defining characteristic of modern society– Narrow breadth and high depth of knowledge/skills – Higher quality at lower cost with better availability

• Services in the real world are– Interchangeable (functionally - individual

goods/providers don’t matter)– Contract-driven (well-known interaction points)– Mechanism independent (black box principle)

• Examples:– Banking, healthcare, restaurants, etc.

Service-Oriented Computing• Service-oriented computing (SOC) applies specialization

and design by contract to design complex software systems– Handles heterogeneous components (interoperability)– Simpler design, reuse, and faster development time

(composition)– Improved fault tolerance and adaptation (interchangeability)

• A software service is an artifact that performs some meaningful function for its client– Well-defined interface (set of methods)– Meta-data to describe the service (set of properties)– Implementation is hidden from clients

• What are some example software services and service-based systems?

Canonical Exercise: ATM Service

• Interface (= methods)?

• Meta-data (= properties)?

• Possible applications?

Service-Oriented Architectures

• SOA is a framework and environment for managing and connecting services– Platform independent API– Execution environment for providers and clients

• Service registry - stores service descriptions and binding information (e.g. phone book)– Providers publish services and descriptions (e.g.

name, interface, endpoint, protocol, etc.)– Clients query for services, filter meta-data, and obtain

binding information for desired services– Execution/invocation not included

SOA Components

12

3

SOA Specifications: OSGi and WS

• OGSi - The Open Service Gateway initiative

– Java-based, centralized SOA standard

– Targets dynamic, collaborative, reactive environments

• WS – Web Services

– XML/HTTP based, decentralized SOA standard

– Composed of three standards: WSDL, SOAP, and UDDI

– Targets business activities and workflows

OSGi Layers

Class loading policies and dependency resolution

Runtime bundle management

Publish, query, etc. service events

Bundle, package, user permissions

Unpacking an OSGi Bundle

Bundle

Activator

Service Implementation

ManifestComponent ResourcesService

Interface

Example Service Interface and Metadata

package edu.iastate.cs.sh.atm;

public interface ATM {

int deposit(int account, int amount);

int withdraw(int account, int amount);

int checkBalance(int account)

}

/* Example property values

-----------------

<“Banks”, “WellsFargo, United Bank of Ryan”>

<“CurrencyType”, “USD”>

<“SOAP.service.name”, “ATM”>

<“SOAP.service.methods” “deposit, withdraw, checkBalance”>

*/

Example Manifest File/* Bundle information

Bundle-Name: ATM /* Human readable */

Bundle-SymbolicName: edu.iastate.cs.sh.atm /*machine-

readable*/

Bundle-Description: service for depositing, withdrawing, and

querying from a bank account

Bundle-Version: 1.0.0

/*Package dependencies */

Import-Packages: …

Export-Packages: edu.iastate.cs.sh.atm

/* Bundle resources */

Bundle-Activator: edu.iastate.edu.sh.ATMActivator

Bundle-Classpath: /* resources inside the bundle */

/* Others ... */

Example Activatorpackage edu.iastate.cs.sh.atm;

public ATMActivator implements BundleActivator {

private ATM atm = null;

private Dictionary props = null;

private ServiceRegistration reg = null;

public void start(BundleContext bc){

atm = new ATM(“ISU Savings”);

props = new Dictionary();

props.add(“BankName”, “ISU Savings”);

props.add(“Currency”, “USD”);

reg = bc.registerService(ATM.class.getName, atm, props);

…

}

public void stop(BundleContext bc){

reg.unregister();

}

}

Lifecycle of an OSGi Bundle

Load

Unload

Unload

Activator

Lifecycle of an OSGi Service

REGISTERED MODIFIED

UNREGISTERING

RegisterModify

Unregister

Activator

Deploying a Bundle: CheapMovies

Registry

?

Event: BUNDLE INSTALLED!

?

BUNDLE RESOLVED!

ATM

ATM

Theater

Activating the Bundle

Registry

Event: BUNDLE STARTING!

getServiceReference(…)

ServiceReference

BUNDLE STARTED!

getService (…)

Service Object

registerService(…)

SERVICE REGISTERED!

“filter”

ATM

ATM

TheaterCheapMovies

Deactivating a Bundle

Registry

Event: BUNDLE STOPPING!

ungetService()

BUNDLE STOPPED!

unregister (…)

SERVICE UNREGISTERING!

ungetService()

ATM

ATM

TheaterCheapMovies

Review: Important Tasks

• Service providers– Define service interface and metadata– Develop an implementation (hidden)– Register a service object with the OSGi framework – Update a service’s properties– Unregister a service with the OSGi framework

• Service consumers– Query the service registry– Examine a service’s properties – Bind to the service object– Invoke the service methods– Release the service

What is Knopflerfish?

• Open source implementation of the OSGi standard– Apache Felix, (Android),

– Equinox (Eclipse)

• Desktop application for graphical monitoring and controlling bundles

• Eclipse plug-in for facilitated development– Generate/edit manifest files, compile source,

– Automatically build and package jar files

The Knopflerfish Desktop

Knopflerfish Desktop Walkthrough

• Starting the framework…

• Monitor bundles/services …

• Examining the manifest file…

• Controlling bundles …

• Refreshing the framework…

• Exiting the framework…

Questions?

• SOC/SOA – www.google.com

• OSGi – www.osgi.org

• Knopflerfish – www.knopflerfish.org

Current Applications

• Current applications

– Home automation

– Health management

– Home security

– ADL support

• Possible extensions?

Possible New Applications

• Generic voice interface

• Prescription conformance monitor

• Exercise monitor

• Universal WebRemote

• EnergySaver

Existing Services (Javadocs soon!)

• Device services– Temperature, humidity, pressure, light level, motion– Touch sensor, pressure sensor, dial, microphone, speakers, barcode,

RFID, network camera, LCD, [biomedical!]– Lamp and appliance control, remote control, [door opener!]– Fridge, microwave, blinds

• Data services– Food, medication, health conditions, medical conflicts, user profile

• Utility services– Speech, notification, [timer, calendar, logging]

• Monitoring services– Diet, inventory, shopping list, expiration date, [prescription, physical

activity,]