Smart Clients

1. Smart Clients What, Why, and Where By: Richard Arthur

2. Smart Clients Defined • Best programming benefits of • Windows applications • Web applications • Benefits are • Smaller footprint • Richer interaction • More robust code • Easier deployment • Consistent updates • Centralized data stores

3. Motivation: Web • Benefits of Web Sites • Easier deployment • Easier upgrades • Ubiquitous access • Centralized data stores • Drawbacks of Web Sites • Managing scale • Less-interactive • HTML – even with JavaScript, it is not great • Stateless • Session management • Limited access to local resources

4. Motivation: Windows • Benefits of Windows Applications • Richer interactions within the application • Faster performance • Better use of local resources • Can be run when disconnected • Drawbacks of Windows Applications • DLL Hell • Installation and upgrade headaches • Larger installations • “Heavy Footprint” – consumes more resources

5. Nifty Graphic http://msdn.microsoft.com/smartclient/understanding/definition/default.aspx

6. Groups of Smart Clients • Windows • Full-blown stand-alone applications • MS Office • Applications use Office for data management • Mobile • Handhelds use Web Services • store and manipulate data

7. MS Office? • Source of confusion • Developers got a little trigger-happy with “Smart Client” term • Employs many design principles of Smart Clients • Outlook • works disconnected • Excel • Easy to update deployed spreadsheets • Centralize data and reference it • Use Web Services • Word • Easy to update deployed documents • Centralize the data and reference it • Use Web Services

8. Existing Applications • Where are smart clients today? • AOL/MSN Messenger • Contact list is centralized • Customizations are stored locally • Seamless application updates • Virus Scanners • McAfee stores local DB of viruses • Regularly updates itself • MS Passport • Centralized storage of Credit Card info • Data shared across web sites

9. Target Environments • Corporate environments • Lots of users • Central/shared data stores • Frequent or important updates • Know OS/Environments • Home environments • Data duplicated/shared across several machines • Frequent or important updates • Bug fixes • New features

10. Considerations For Implementing • Consider Smart Clients when your code can/may: • Replicate data across several applications • Data should be centralized for all users • Application needs desktop resources to work • Needs more power than web apps can provide • Application needs connectivity • Can do without it for a while

11. Facilitating Smart Clients • .NET Framework • Overcoming DLL Hell • Version conflicts • “XCopy” deployment • “No-Touch” deployment • Overcoming large footprint • Many assemblies already exist on client machines • Intermediate code is inherently smaller • Visual Studio .NET 2005 • Overcoming Deployment/Upgrade issues • ClickOnce technology

12. XCopy Deployment • Old DOS tool for copying several files at once • No registry needed • Some drawbacks • You may need data pre-installed to the registry • You may need data pre-installed outside the install directory • User data should go in the UserAppDataPath directory • No transacted installs • Currently provided by the Windows Installer

13. No-Touch Deployment • Post to Web/Shared Server • Runs from the download location • Downloads assemblies on demand • Drawbacks: • Unreliable offline functionality • May not have the latest DLLs • DLLs might be cleaned up by IE • Apps can run in “offline” mode only when IE is in offline mode • Same DLL problems as mentioned above

14. More No-Touch Problems • Runs in “sandbox”-like environment • No access to • Global Assembly Cache (GAC) • Unmanaged code • Registry • Windows Shell • Any Files – except for “Isolated Storage” • Databases • Other Applications • Web Sites other than the originating server

15. Major Design Considerations • Several areas must be considered • Data • Network • Security • Deployment & Upgrading See: http://msdn.microsoft.com/smartclient/default.aspx?pull=/library/en-us/dnpag/html/scag.asp for greater details

16. Data Considerations • Central Store • Access from several locations • Share between different users • Local store • No need to share • Store locally for the application • Need to be disconnected • Update regularly: prevent stale data • Update asynchronously: allow interaction while updating

17. Networking Considerations • When connected • What will you let your users do? • Limit network “chatter” • Make it look fast, ensure completion later • Improves performance (real & perceived) • When disconnected • Use a data store to allow continuous operation • Managing updates when reconnected • Handling dependencies (key-based relationships) • When interrupted • Detecting interruptions to Network service • Recovering from interruptions • Ensuring no data corruption

18. Security Considerations • Trust No Data! • On the server: • Authenticate and Authorize all requests • Always double-check the data • SSL Encryption is good, but still a stop-gap • Centralize server access • Write consistent code • Write hole-free code • Manage resource permissions properly • On the client: • Validate all the data • Authenticate and Authorize all incoming data • Read “Writing Secure Code” (ISBN:0735617228)

19. Deployment Considerations • Make sure all clients have the .NET Framework • OneClick • Easier to maintain and upgrade • Not available with .NET Framework 1.1 • No-Touch • Easy to maintain on the server • Harder to maintain on the client • Windows Installation Package • Easy for developer to maintain • Harder to upgrade the application • May combine with OneClick • Download and automatically install periodic updates

20. Thank You Questions?