Building Frameworks With Patterns

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Building Frameworks With Patterns

• An Active Object-Model For A Dynamic Web-Based
  Application

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Presenters

• Joseph W. Yoder -
• j-yoder_at_uiuc.edu
• http//www.uiuc.edu/ph/www/j-yoder
• Dragos Manolescu -
• manolesc_at_uiuc.edu
• http//www.uiuc.edu/ph/www/manolesc

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Goals

• Have fun
• Learn a little about our framework
• Overview of patterns used in the framework
• See how to implement the patterns using Java

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Outline

• Project Overview
• Active Object-Model
• Overview of Frameworks
• Preview of Patterns in the Framework
• Architecture Design of the Framework
• Patterns in the Framework
• Future Development
• Summary

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Active Object-Model(Dynamic Object-Model)

• An ACTIVE OBJECT-MODEL is an object model that
  provides meta information about itself so that
  it can be changed at runtime
• explicit object model that it interprets at
  run-time
• change the object model, system changes its
  behavior
• ACTIVE OBJECT-MODELS usually arise as
  domain-specific frameworks
• Business rules can be stored in ACTIVE
  OBJECT-MODELS

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Purpose Of ProjectOn-line Registration

• Develop reusable Software System to be used for
  on-line Conference Registration
• Customizable
• Different Reports
• Different databases
• Different Business Logic
• Composable

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Requirements

• Web Access
• Easy to Use
• Secure
• Platform Independent
• Integration with Legacy Databases
• Robust

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How to DevelopReusable Software

• Reusable software is hard to develop
• Generalize from examples
• Refactor to pull out common parts
• Develop special interface/language for specifying
  application

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Frameworks

• Interface design and functional factoring
  constitute the key intellectual content of
  software and are far more difficult to create or
  re-create than code.
• Peter Deutsch
• Difference between framework and component
  library for framework (components get plugged in
  and are concrete sub-classes that do all the
  work).
• For detailed information about Frameworks attend
  Ralph Johnsons tutorial or see
• http//st-www.cs.uiuc.edu/users/johnson/
• or http//www-cat.ncsa.uiuc.edu/yoder/Research/F
  rameworks

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Frameworks Encode Domain Knowledge

• Frameworks solve particular sets of problems.
• get different points of view
• explain/defend current design
• Some frameworks are more technology (horizontal)
  frameworks verses application domain (vertical)
  frameworks.
• Are we solving GUIs, object persistence verses
  more application domain related such as
  insurance, medical,or manufacturing.

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Frameworks

• Framework is
• reusable design of an application or subsystem
• represented by a set of abstract classes and
  the way objects in those classes collaborate.
• Use framework to build application by
• Creating new subclasses
• Configuring objects together
• Modifying working examples

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Frameworks

• Framework prescribes how to decompose a problem.
• Not just the classes, but the way instances of
  the classes collaborate.
• shared invariants that objects must maintain, and
  how they maintain them
• framework imposes a collaborative model that you
  must adapt to.

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Relevant Principles

• Frameworks are abstractions people generalize
  from concrete examples
• Designing reusable code requires iteration
• Frameworks encode domain knowledge
• Customer of framework is application programmer

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Generalize from Concrete Cases

• People think concretely, not abstractly.
• Abstractions are found bottom-up, by examining
  concrete examples.
• Generalization proceeds by
• finding things that are given different
  namesbut are really the same,
• parameterizing to eliminate differences,
• breaking large things into small things so that
  similar components can be found, and
• categorizing things that are similar.

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Finding Abstract Classes

• Abstract classes are discovered by generalizing
  from concrete classes.
• To give two classes a common superclass
• give them common interface
• rename operations so classes use same names
• reorder arguments, change types of arguments,
  etc.
• refactor (split or combine) operations
• if operations have same interface but different
  implementation, make them abstract
• if operations have same implementation, move to
  superclass

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Frameworks Require Iteration

• Reusable code requires many iterations.
• Basic law of software engineering (Johnsons law)
• If it hasn't been tested, it doesn't work.
• Corollary software that hasn't been reused is
  not reusable.

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White-box vs. Black-box
Black-box Customize by configuring Emphasize
polymorphism Must know interfaces Complex, harder
to design Easier to learn, requires less
programming. Harder to customize because you
need to learn how objects collaborate

• White-box
• Customize by subclassing
• Emphasize inheritance
• Must know internals
• Simpler, easier to design
• Harder to learn, requires more programming.
• Easier to customize because you can overwrite the
  code

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Patterns for Developing Frameworks

• 1) Three Examples
• 2) White-box Framework
• 3) Component Library
• Build applications and add components to library
• 4) Hot Spots
• Separate Changeable from Stable Code
• Design Patterns

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Patterns for Developing Frameworks

• 5) Pluggable Objects
• 6) Fine-grained Objects
• 7) Black-box Framework
• 8) Visual Builder
• 9) Language Tools
• http//st-www.cs.uiuc.edu/users/droberts/evolve.ht
  ml

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Mapping Objects To Persistence Pattern Language

• Persistence Layer
• CRUD
• SQL Code
• Attribute Mapping Methods
• Type Conversion

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Mapping Objects To Persistence Pattern Language

• Changed Manager
• OID Manager
• Transaction Manager
• Connection Manager
• Table Manager

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Security Patterns
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Architecture

• To be presented by Dragos Manolescu
• http//www-cat.ncsa.uiuc.edu/yoder/Research/PLoP/
  arch.html

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Future Development

• Metadata stored in database
• Visual Builders and Editors
• Debugging Tools
• Distribution through CORBA etc

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Patterns used in the System

• GOF Patterns
• Strategy, State, Singleton, Composite, Factory
  Method, Prototype
• Layered Architecture
• Security Patterns
• Limited View, Single Access Point, Roles, Check
  Point, Session, Secure Access Layer
• Persistence Object Patterns
• Attribute Mapping Methods, Transaction Manager,
  OID Manager, Change Manager, CRUD, Type
  Conversion, Connection Manager, Table Manager,
  Persistence Layer
• Type-Object, Properties, Metadata
• Evolving Frameworks

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Summary

• We have developed a reusable designfor on-line
  registration
• Patterns can be very useful for solving problems
  in your domain
• Frameworks take time to develop butthe payoff
  can be tremendous

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Where to Find more Information

• http//www-cat.ncsa.uiuc.edu/yoder/Research/PLoP
• http//www-cat.ncsa.uiuc.edu/yoder/Research/metad
  ata
• http//st-www.cs.uiuc.edu/users/droberts/evolve.ht
  ml
• http//www-cat.ncsa.uiuc.edu/yoder/papers/pattern
  s
• http//hillside.net
• http//st-www.cs.uiuc.edu/

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Thats All