Building Composite Applications

Jeremy Boyd

Mindscape

Lots of ground to cover!

New concepts, code!

Look for code, samples and presentation downloads

http://turtle.net.nz/blog/

Jeremy@mindscape.co.nz

Composite Applications

• The whole is greater than the sum of its parts
• Composed of a number of discrete and independent pieces, aggregating this functionality through a software interface.
• Break free from “silo” issues
• Lower cost of development
• Consistency

Tradition Applications

• An encapsulated system providing its own self sufficiency

What’s enabled all this?

• Services
• Software over services
  • Lightweight
  • Loosely coupled
  • 3 tier architecture
• Result: Reuse of software!

Traps to watch for

• Maturity for integration
  • Must be able to leverage services for direct integration for greatest benefit
• External Trust
  • External data lives in the cloud
  • Reliance on provider for business operations

Example: Exchange Server 2007 is used by

• Outlook
• Outlook Web Access
• Outlook Voice Access
• Outlook Mobile

Background Motion

• Lightweight build: 3 weeks
• Consumes resources from
  • Flickr
  • Soapbox
  • GeoTagIt
• Also publishes services and data

Architecture

• Presentation Layer = ASP.Net 2.0 & AJAX
• Business Layer = Content Service, controllers & Model
• Resource Layer = Service Proxies & LINQ to SQL Server

But How?

• Start with the problem e.g. Provide a community site to provide content for DreamScene
• Focus on the interface
• Work out who is already offering functionality
  • Flickr works well for images
  • Soapbox works well for videos

We already had great tools

• .NET 2.0 and .NET 3.0 Frameworks
• ASP.Net AJAX
• Composite Web Block
• Enterprise Library
• Don’t forget about 3^rd party!
  • RSS Toolkit
  • Lucene.NET
  • 2 way data-binding

Some tips from the Background Motion build

• WebDataBinder
  • DataBinder.DataBind()
  • DataBinder.Unbind()
• Microsoft.Practices.EnterpriseLibrary.Validation
  • [RequireValidator]
  • Presenter.Save()

Supervising Controller (MVP)

• View (GET http://site/pages.aspx)
• Presenter (View is based on the PageBase class which wires it up to the Presenter)
• Model (View can work with the Model but calls back to Presenter to perform process flow)

• “Factor the UI into a view and controller where the view handles simple mapping to the underlying model and the controller handles input response and complex view logic.” Martin Fowler – www.martinfowler.com
• Cleanly separates UI process form binding/event logic
• Improves testability

Dependency Injection

• Establish a level of abstraction via a public interface, and remove dependency on components by (for example) supplying a plug-in architecture – Wiki
• Allows for loose coupling
• Abstraction through interfaces
• Composite Web Block uses
• ServiceLocator approach

Service Locators

• I need an instance of IDataLayer class! (Consumer to Interface)
• I can ask the ServiceLocator to give me an instance of IDatalayer
• ServiceLocator holds an instance of Factory <IDataLayer>
• Factory <IDataLayer> assembles a Concrete class instance
• Concrete instance is returned to the Consumer
• Consumer always calls through the IDataLayer interface

So What?

• Solid foundation leads to flexibility – supports change!
• Lower development complexity – modularity!
• Testability of solution
  • More effective integration
  • Shorter cycles
  • Always building working code!

Unit Testing…

• Create a separate library (project in the solution)
• NUnit – a free testing framework
• Define [Test] methods
• Assert.IsFalse(contribution.ValidationResults.IsValid);
• (do some work)
• Assert.IsTrue(contribution.ValidationResults.IsValid);
• Where might these be useful?
• When a field length changes, the Unit Test will fail the Validator.
• Helps save you a lot of time by capturing these types of failures

Continuous Integration

• Developer checks in to source control
• The BuildServer monitors the source control
• The BuildServer builds the application
• The BuildServer runs the unit tests
• The BuildServer notifies whether all tests passed

Resources

• External from this application
  • Active Directory
  • Web Services
  • Legacy System
• Contract based consumption
  • Loose coupling
  • Flexibility in plug and play

But how?

• Windows Communication Foundation
• The Unified Framework for rapidly building service oriented applications

WCF

• Building block for building Connected Systems
• Designed around messages!
• Full standards/specifications support (WS-* oriented)
• Provide consistent API regardless of messaging requirement
• Part of .Net 3.0 Framework

Software + Services

• ASP.NET AJAX. The free framework for quickly creating a new generation of more efficient, more interactive and highly personalized Web experiences
• Building a mash-up using ASP.NET AJAX
• Web Service can output AJAX (JavaScript)!

AJAX with Services

• ASP.Net AJAX allows native call
• Too fast

Call to Action

• Read about Patterns
• Look at Unit Tests and CI http://ccnet.thoughtworks.com
• Download the Composite Web Block
  • And the Validation Block
  • And the Enterprise Library
• Publish services in your enterprise to allow composite applications to flourish!