Developing%20Object-Oriented%20Systems

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Developing Object-Oriented Systems
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Course Topics

• Introduction to Object-Oriented Analysis and
  Design
• Object-Oriented Concepts
• Visual Modeling with UML
• Developing Object-Oriented Systems
• Transition from OO models to code
• Distributed architecture
• OO and Persistence

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Moving From OO Design to Code

• The UML is simply a language used for designing
  OO systems
• Development of an object-oriented software system
  also requires tools and a process
• Tools IDEs, compilers, test tools,
  configuration management, etc.
• Process RUP, unified process, waterfall, RAD,
  agile, etc.

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Characteristics of OO Systems

• Object-oriented software solutions are
• Use Case driven
• Visually modeled
• Iteratively developed
• Continuously verified
• Reuse focused
• Component based
• Architecture centric

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Unified Process - Reviewed
Phases
Disciplines
Business Modeling Requirements Analysis and
Design Implementation Test Deployment Configuratio
n Management Project Management Environment
Iterations
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Iterative Development
3. Requirements
4. Analysis Design
2. Planning
1. Initial Planning
5. Implementation
Management Environment (on-going)
6. Test
8. Evaluation
7. Deployment
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From Use Cases to Design

• The process starts with Use Cases to
• Capture requirements
• Model the business rules of the system in terms
  that all can understand
• Describe the system at a very high level
• Plan for development
• Plan for testing

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Realizing Use Cases
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Steps in Realizing the Use Case

• The completed Use Case model includes
• Use Case diagram
• Detailed descriptions
• Activity diagrams to model the descriptions

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Steps in Realizing the Use Case (Cont)

• From completed Use Cases, the next steps are
• Generate a conceptual class diagram for the
  classes in the use case
• Generate high-level interaction diagrams
  (communication diagrams?)
• Generate state machine diagrams as needed
• Refine interaction diagrams (sequence diagrams?)
  with fully specified methods
• Refine and fully specify the class diagram based
  on the preceding diagrams
• Develop code from fully specified classes
• Test unit, integration, sub-system, etc.

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Class Design Considerations

• Look at each class and define
• Methods
• Found in sequence diagrams and state machine
  diagrams
• Consider object construction and destruction
• Data
• Found in state machine diagrams
• Inferred from roles designated in class diagram
• Specify type and meaningful name
• Be sure to specify access levels correctly
  public and private
• Look for reuse through inheritance
• Consider opportunities to exploit polymorphism

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A Fully Defined Class ?

• Details of the class begin to take shape as we
  search other diagrams for content

Access Symbols private public
protected package
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Converting from Traditional Languages

• Problem developing in a pure object-oriented
  language like Java requires a developer to think
  about application logic in very abstract ways
• Remember that objects are created to accept
  messages and exist in an event-driven environment
• Efficient development in Java requires
  partitioning application logic GUI design,
  remote data access and execution mechanisms,
  network features, OS specific features, etc.
• The developer has to learn to deal with
  client-server architecture also

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Distributed Processing

• Distributed processing Computer processing in
  which different parts of a program run
  simultaneously on two or more computers
  communicating over a network
• Versions
• File Server
• Early implementations
• Supports the distribution of data only
• Client / Server
• More versatile and commonly used today
• Supports the distribution of both data and
  processing

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Distributed Processing - File Server

• Client
• Process/scan tables
• Application programs
• user interface
• database processing
• generate queries
• Handle integrity and security
• Full DBMS

• Entire file is transferred

Client request for data Server entire file
transferred

• File Server
• File storage
• Record locking
• Significant LAN traffic

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Distributed Processing Client/Server

• Typically client is smaller PC and server is
  larger processor
• Application software divided (not equally)
  between client and server
• Client typically manages user interface
• Server typically responsible for database storage
  and access, including query processing

Client request for data
Only result of request
Client
Server
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Variations of Client / Server Architecture

• Four flavors of client / server architecture
• Thick client much application processing in the
  client server acts more as a database server
• Three tier normal client, business object
  server, database server
• Thin client client handles most of the
  presentation logic, all other processing done in
  server
• Peer-to-peer any process node can be both
  client and server

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Three-Tier Client / Server Architecture

• Logical partitions may be more than three
  physical nodes
• Provides a pattern for scalability by adding
  servers and rebalancing processing across data
  and business servers

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Components

• Components self-contained elements of software
  that can be controlled dynamically and assembled
  to form reusable applications
• Another exploitation of the OO principle of
  encapsulation
• Will typically have a controlled, well-defined
  interface and will support polymorphic behavior
• Can be used in an application without
  modification and are used independently of the
  context in which their services are requested

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Component Technology Examples

• Common Object Model (COM)
• Microsoft standard for component architecture
• ActiveX - technology used for developing reusable
  object oriented software components
• Somewhat replaced by the .NET capabilities
• JavaBeans
• Reusable Java components
• Generally deal with visual capabilities screen
  controls

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Distributed Components

• For components to be completely reusable and
  plug-able, they must have a standardized
  interface which allows for
• Components developed in different programming
  languages
• To communicate seamlessly over different
  networks
• To be executed on different platforms
• The interface must allow for execution of an
  object on a host machine by an object on a
  connected machine as if they were in the same
  machine
• There are many products and technologies that
  support this standard called Object Request
  Brokers (ORBs)

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Object Request Brokers

• ORB A mechanism for invoking operations on an
  object in a different process that may be running
  on the same or a different computer
• At a programming level, these remote calls look
  similar to local calls
• Sometimes referred to as middleware allowing
  stand-alone applications to communicate with each
  other
• A few middleware implementations
• CORBA The open-source daddy of all ORBs
• SOAP Simple Object Access Protocol
• RMI Javas Remote Method Invocation
• COM and .NET Microsoft
• MQSeries IBM

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Generic ORB Architecture

• Brokers are message-passing media which keep
  track of the client/server objects they manage
• Proxies implement the same interface as the
  client/server objects the Client calls the
  server Proxy, and the Server returns information
  to the Client Proxy

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CORBA

• CORBA Common Object Request Broker Architecture
• Managed and controlled by the OMG
• Specifies a set of services for object creation,
  deletion, access, persistence, defining external
  relationships, etc.
• Some vendor products that provide these services
• Orbix (Iona) an enterprise CORBA implementation
  product
• VisiBroker (Borland) a CORBA infrastructure
  product
• ObjectBroker (BEA Systems) a CORBA compliant
  production tool
• CORBA objects are
• Implemented as an instance of an interface type
• Written in the Interface Definition Language
  (IDL)
• C like data declarative language (no control
  statements)
• Creates a binary form of the object

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CORBA Architecture

• The ORB transmits method calls from Client to
  Server, and back to Client

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Remote Method Invocation - Java

• RMI is Javas built-in middleware technology
• Works for java built objects only not supported
  by Microsoft
• In RMI the client proxy is called a stub and the
  server proxy is called a skeleton

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More on RMI

• Java has a special tool called remote method
  invocation compiler (rmic ) that produces the
  stub and skeleton for the remote call
• Information about available remote methods is
  kept in the RMI registry this is where the
  stub will look up the location of the method to
  be called
• Another tool called rmiregistry should be run at
  the time of execution to establish the registry
• Because the method call uses the network, the
  client code must provide for possible network or
  I/O exceptions

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Simple Object Access Protocol - SOAP

• SOAP stands for Simple Object Access Protocol
• SOAP is a communication protocol between remote
  applications sending messages via the internet
• SOAP is based on XML and is platform independent
  and language independent
• SOAP is simple and extensible
• SOAP allows you to get around firewalls

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More on SOAP

• SOAP uses the Internet application layer protocol
  (HTTP) as its transport protocol
• Because SOAP uses XML as its language, it is
  extensible users can create their own tags
• SOAP is a key element of Microsoft's .NET
  architecture for internet application
  development.
• SOAP has been developed as a W3C standard
• W3C a consortium of companies setting standards
  for web behavior

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OO and Persistence

• Persistence is simply the concept of saving and
  restoring data from a program to and from a data
  base
• In OO systems this involves saving and restoring
  complex objects
• Remember, just the data or state of the object
  must be saved and restored
• The most common data base management systems in
  use today are relational (RDBMS) like Oracle,
  Informix, DB2, etc.

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Difficulties In OO Persistence

• There are difficulties with persistence and
  complex objects
• If the to-be-saved/restored object has aggregated
  objects, they must be saved and restored also
• If the object involves inheritance, both child
  and parent data parts must be saved and restored
• Storing and retrieving complex objects using a
  RDBMS poses a problem of
• Flattening out the object for writing to the
  data base called serialization
• Re-inflating the object when read back into
  your OO program called deserialization
• Moving the data back and forth (in serialized
  format) is called marshalling

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OODBMS

• OODBMS Object-Oriented Data Base Management
  System Combines object-oriented programming
  principles with database management principles
• Stores objects in a format nearly
  indistinguishable from the objects supported by
  the target programming language accommodates
  aggregation and inheritance
• Industry tends to lean away from OODBMS and use
  RDBMS with some form of transformation capability
  to deal with complex objects

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Moving OO Data To/Form an RDBMS

• A solution
• Identify classes that have persistent objects and
  add load() and store() methods to each class to
  handle formatting, writing and reading directly
  to the database
• This presents a tight coupling problem
• A better solution
• Create an abstraction layer that has classes that
  deal with objects and the database
• Create a special class for each persistent class
  a Data Manager (DM) class
• Knows how to pack/unpack an object for an SQL
  statement
• Create a special class for dealing with the
  database directly a DBServer class
• Handles connectivity
• Generates and issues SQL commands

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OO Data To/From a RDBMS
Tightly Coupled

• Problems with the tightly coupled version
• Changing the DB vendor becomes a nightmare
• Lots of extra processing in each problem domain
  class that must be saved

Layered
Problem Domain
Data Management Domain
CourseOffering
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Review

• What are the three components of software design?
• Name four of the seven characteristics of OO
  systems.
• What is distributed processing? Why is it so
  popular?
• What is a component?
• What are Object Request Brokers?
• What is the Java ORB or middleware technology
  called? How does it work?
• What are the problems with reading and writing a
  complex object to a relational data base?

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Any Questions?