Distributed Smart Client Applications

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• Distributed Smart Client Applications
• November 2004

Jay Traband, CTO jayt_at_ideablade.comwww.ideablade.
com
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Glad to be here
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What is a Distributed Smart Client?

• Distributed
• Processing in multiple places
• Data in multiple places
• Smart Client
• Maximized client-side processing
• Presentation layer
• Business logic
• Ability to run disconnected
• One-click deployment

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Typical 3-Tier Architecture
DataTier
MiddleTier
ClientTier
Internet
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Business Object Persistence

• How do I get data out of my database into my
  business objects?
• Do I pick a specific database vendor or write
  vendor neutral code?
• Do my developers all need to know SQL? If so how
  do I isolate it?
• How much business logic do I put in the database
  (stored proc/triggers etc)?
• How do I handle concurrency, transactions, and
  multiple databases?

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What is a Business Object?

• An instance of a class with . . .
• Business data - Salary
• Business logic - GarnishWages()
• Business events - SalaryChanged
• Persistence
• Identity

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Persistence Options
DataTier
BusinessModel
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Why Object-Relational Mapping

• Decouple object and database semantics
• Encapsulate database schema
• Database derived properties look the same
• employee.BirthDate, employee.Age
• Object graph navigation
• dot notation vs. n-way joins
  sub-selectscustomer.Address.City vs. Select
  City from Address where Address.Id
  Customer.AddressId and Customer.Id12345
• Minimize or eliminate developer SQL
• Custom and conflicting SQL
• Stored Procedures
• Database independence

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Enterprise-class ORM

• Separate business object developers from
  consumers
• Hide / filter / extend business objects for
  consumers
• In-memory, fine-grain object cache
• Offline mode local persistence
• Object query language
• Views, stored procedures, user-defined fields
• Round-tripping handle triggers db calculations
• Transactions optimistic concurrency
• Database independence

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Business Object Mobility

• How do I move business objects between the object
  server and the client?
• Do I use web Services, remoting, message queues
  or all of the above?
• How do I handle firewalls proxy servers?
• Should I pass data, objects or distributed refs
  to objects?
• How do I provide security?
• Authentication / Authorization
• Secure execution context code access security
• What performance / scalability tradeoffs am I
  making?

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Distributed Processing Issues

• Object oriented design conflicts withScalable
  distributed design
• Object methods and properties are fine
  grained,distributed methods are chunky
• Object mobility (marshal by value vs marshal by
  ref)
• Data Locality data close to where used
• Stateless objects for scalabilityStateful
  objects for ease of development
• Session info, load balancing threading

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Distributing Data / Objects
DataTier
MiddleTier
ClientTier
Scalability, Reliability
Too Fine Grained
Data, not Objects
Object Fidelity
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Where is the Business Logic?
Data Tier, Middle Tier, Client Tier ?

• Middle Tier the standard answer
• Logic all in one place
• Security
• Middle Tier (some in Data Tier)
• Performance
• - Encapsulation
• Client Tier and Middle Tier (Object mobility)
• Logic still in one place the business object
• Business object execution space can vary
• Best performance
• Security is shared between the tiers

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Client Side Processing

• How do I manage my business objects on the
  client?
• How do I keep them in synch with the server?
• Do I cache business objects on the client?
• How do I handle large object graphs?
• How do I operate when not connected to the
  server?
• How do I query for objects on the client?
• How do I keep my user interface in synch with my
  business objects?
• How do I insure that any change to a business
  object appears in the user interface?
• How do I insure that refreshed data from the
  object server appears in the user interface?

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ModelViewController
Controller
Model
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Distributed Smart Client Architecture
DataTier
MiddleTier
ClientTier
Controller
Model
View
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Jay Traband, CTOjayt_at_ideablade.comwww.ideablade.
com
Thanks For Your Time