E188 Best Practices in Object-Oriented Modeling Using PowerDesigner

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E188 Best Practices in Object-Oriented Modeling
Using PowerDesigner

• Donald D. Clayton
• President
• Intertech Consulting, Inc.
• Dclayton_at_intertech.us

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Objectives

• Understand the ways modern systems are becoming
  increasingly complex
• Review the differences between traditional
  client/server practices and three-tier and
  distributed computing.
• Learn practical design techniques for managing
  this complexity
• Understand how to use PowerDesigner and UML to
  control this complexity

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Topics

• Modern System Development Architectures
• Brief History of UML
• UML Views
• UML Phases

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Modern System Development Architectures

• Enterprise systems have increased in
  sophistication from early days of Client/Server
• Todays business systems need to support a
  variety of client types
• In this environment, it difficult to impossible
  to RAD the application
• UML gives us the semantics to support these
  efforts
• PowerDesigner gives us the tool to support these
  efforts

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Distributed Application Development
Client
Middle Tier
Data
Web Server
Browser
Very Thin
PageServer
ProductionData
FileSystem
HTML Pages
ProductionData
Templates, Scripts
Browser or C/S
Thin
TransactionServer
ProductionData
Components
Components
ProductionData
Enterprise JavaBeans, COM, CORBA, PB NVOs
Client/ServerApplication
Rich
ProductionData
Components
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So Where Does PowerDesigner Fit In?

• The PowerDesigner program is a powerful tool that
  can be used by a variety of users with different
  backgrounds
• Business Analysts
• Database Administrators
• System Programmers
• Your role, the point in the systems development
  process, and the technology set you are using all
  determinants in using PowerDesigner

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Data Modeling Lifecycle
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Differences Between Model Types

• The CDM, PDM, and OOM models are intended for
  different audiences with different needs
• How PowerDesigner is used depends partially on
  the background and role of the person using it.
• Conceptual Data Models
• Good for Business Analysts and DBAs
• Physical Data Models
• Good for DBAs and System Developers
• Object-Oriented Models
• Good for System Developers and DBAs

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The Unified Modeling Language (UML)

• A plethora of modeling approaches threatened to
  stymie the use of OO techniques
• The OMG requested a proposal for a standard
  notation for object-oriented systems, now called
  Unified Modeling Language, or UML
• UML has its origins in several Object-Oriented
  Methodologies
• Rumbaugh et al. OMT
• Booch methodology
• Jacobson's methodologies
• PowerDesigner 9.0 OOMs use four UML diagram
  types, 9.5 will have 9 diagram types

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The UML and Object-Oriented Modeling in
PowerDesigner

• PowerDesigner provides the following types of UML
  diagrams
• Class Diagram
• Use Case Diagram
• Sequence Diagram
• In PowerDesigner 9, support was added for
• Activity Diagram
• Component Diagram
• PowerDesigner 9.5 will add support for additional
  UML models, for a total of 9 UML model types

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The Views In UML
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The Phases In UML
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Inception Phase

• Purpose
• To establish the business case for a new system
  or for a major update of an existing system
• Required products
• A high level understanding of the business
  processes (Business Process Models)
• The core requirements for the project (Use-Cases)
• An initial risk assessment
• Optional products
• A conceptual prototype
• An initial domain model (10 - 20 complete)

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What is a Business Process Model?

• A Business Process Model (BPM) is a model that
  provides a description of the business logic and
  rules from a functional point of view
• A BPM uses diagrams that show interactions
  between processes, flows, messages and resources
  from one or several start points to all potential
  end points
• The BPM is a simplified UML activity diagram with
  Business Process extensions
• It can be readily used as an input document to do
  object-oriented analysis

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Objects in a BPM

• A Business Process Model is comprised of a
  variety of components, including
• Processes
• Organization Units
• Starts
• Ends
• Flows
• Decisions
• Resources
• Message Formats
• Synchronizations

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BPM Example
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Use Case Diagrams

• Illustrate actors and their interaction with use
  cases
• Use cases appear as ovals
• Actors appear as stick figures
• Association line connects an actor to a use case
  and represents communication between them

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Use Case Diagrams

• Also show relationships between use cases
• Can be used to show dependency between actor
  roles
• Initiating actor is on the left of the use case
• Receiving actor is on the right
• Rectangle represents the system boundary
• Encloses the use cases, actors should be outside
  the system

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Use Case Documentation

• Use case documentation consists of
• A brief description
• Identification of the actor who initiates the use
  case
• Preconditions for the use case
• Detailed flow of events
• Exception or error handling details
• Post-conditions when use case is complete
• Actor who benefits from the use case
• Can also list assumptions for the particular
  scenario or use case path
• Should use problem domain terms class names can
  be used as nouns in the use case text

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Use-Cases And Scenarios

• Use-Cases
• Describe a set of potential scenarios
• Finite number for a system
• Good for focusing development effort
• Can be leveled like data flow diagrams
• The Uses Association
• The Extends Association
• Scenarios
• Specific instances of a use-case
• Described by event traces, or object interaction
  diagrams.
• Good for test cases

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Use-Case Model - Benefits

• The use-case model
• Provides buy-in at an early stage of system
  development
• Ensures a mutual understanding of the
  requirements
• Is used to identify
• Who will interact with the system and what the
  system should do
• What interfaces the system should have
• Is used to verify
• All requirements are captured
• That the developers have understood the
  requirements

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Elaboration Phase

• Purpose
• To analyze the problem domain
• To establish a sound architectural foundation
• To address the highest risk elements of the
  project
• To develop a comprehensive plan showing how the
  project will be completed

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Class Diagram

• A class is a category or group of things that
  have similar attributes (properties) and common
  behavior (operations)
• An object is an instance of a class
• A specific thing that has specific values of the
  attributes
• Class diagrams describe the types of objects in
  the system and the structural relationships
  between them

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Class Diagram Symbols

• A rectangle divided into 3 sections
• Name
• Attributes
• Operations
• Lines connect rectangles to show relationships

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Types of Classes - Entity Class

• An entity class models information and associated
  behavior that is generally long-lived
  (persistent)
• It can reflect a real-life phenomenon
• It may also be needed for the internal tasks of
  the system
• The values of its attributes are often provided
  by an actor
• The behavior is surroundings-independent

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Types of Classes - Control Class

• A control class models control behavior specific
  to one or more use-cases
• A control class
• Creates, initializes and deletes controlled
  objects
• Controls the sequencing or coordination of
  execution of controlled objects
• Controls concurrency issues for controlled
  classes
• Is, most of the time, the implementation of an
  intangible object

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Types of Classes - Boundary Class

• A boundary class models communication between the
  systems surroundings and its inner workings
• Typical boundary classes
• Windows (user interface)
• Communication protocol (system interface)
• Printer interface
• Sensors
• In the Order Entry scenario, an OrderWindow is
  created to accept information from the user

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Construction Phase

• Purpose
• To incrementally develop a complete software
  product which is ready to transition into the
  user community
• Products
• A stream of executable releases
• Behavioral prototypes
• Quality assurance results
• System and user documentation
• Deployment plan
• Evaluation criteria for at least the next
  iteration

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Interaction Modeling During Design

• Interaction modeling can be done during
  elaboration, if necessary, but is more typically
  a construction modeling technique
• From the what to the how
• Goals of interaction modeling
• Allocate behavior among objects
• Show detailed interactions that occur over time
  among objects
• Finalize the distribution of operations among
  classes

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What Is a Sequence Diagram?

• In a functioning system objects interact with
  each other
• These interactions occur over time
• Objects interact by sending messages to each
  other
• A message stimulates an object to perform some
  activity
• UML Class diagrams represent static information
  and relationships
• UML Sequence Diagram shows the time-based
  dynamics of the interactions
• Represents a major work product of the design
  process

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Sequence Diagrams and Multi-tier Systems

• Sequence diagrams are indispensable for the
  development of multi-tier systems
• The interaction and coordination between objects
  on different tiers is often complex
• Example Interaction occurs between business
  logic objects on one tier, database objects on
  another tier, and multiple types of interface
  objects (e.g, browser, PDA or Windows)
• Sequence diagrams can graphically represent these
  interactions making it much easier to understand
  them

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Components of a Sequence Diagram

• Objects
• Represented as rectangles along the top of the
  diagram
• Actors may be represented but are optional
• Messages
• Represented as arrows
• Time
• Represented in the vertical direction
• Objects lifeline is a dashed line extending
  downward from the object
• Duration of an operations execution (Activation)
  can be represented as a thin rectangle along the
  lifeline of the object (optional)

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Sequence Diagram Example
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PowerDesigner During the Construction Phase

• PowerDesigner 9 supports a number of
  object-oriented languages and technologies,
  including
• PowerBuilder
• Java
• C, C
• CORBA
• Visual BASIC 6
• XML
• During the construction phase, PowerDesigner can
  be used to generate class definitions in several
  of these languages, and can also be used to
  reverse-engineer existing code.

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Transition Phase

• Purpose
• To transition the software product into the user
  community
• To deal with Deployment issues
• Products
• A stream of executable releases
• Quality assurance results
• Updated system and user documentation
• Post project analysis of project performance

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Deployment Diagrams in PowerDesigner
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The Challenges of Persisting of Objects in
Relational Databases

• Mapping objects to relational databases is
  challenging!
• There are (at least) three distinct ways to map
  objects to databases
• Map class attributes to table columns
• Map Java classes to table columns
• Use the Sybase DataWindow/Datastore Technology

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Entities and Attributes in the Real World

• The distinction between entity and attribute may
  seem clear, but it is not at all clear in
  practice
• An address may be seen as an attribute of a
  customer, but an address is also an entity, with
  its own attributes of street, city, and so on,
  and subtypes such as foreign or domestic address.
  
• The utility of an object-relational database lies
  in exactly the fact that there are two ways of
  expressing entities. You can express some
  entities as tables, and some entities as classes
  in a table

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Map Class Attributes to Table Columns

• This is the default approach when using
  PowerDesigner
• Classes, associations, and generalization will be
  mapped to tables
• Class attributes map to columns in a table
• Allows for indexing and querying on attributes
  using SQL
• Allows for conditional retrieval based on
  attributes
• Allows attributes to be retrieved without
  instantiating the classes, e.g., for reporting
  purposes
• Most complicated method for mapping objects to
  databases, but allows for fine control over query
  and access
• PowerDesigner has OR/Mapping technology to make
  this easy

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Map Java Classes to Table Columns

• You can use Java classes as SQL user-defined data
  types
• Store Java objects in database tables as a column
  
• By using a Java class as a data type for a column
  in a table, you can store data in your database
  in the form of Java objects.
• You can access Java operations and attributes of
  Java objects in SQL statements through JDBC.

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Levels of Abstraction for Relational Data

• Java classes are useful for abstracting at a
  level between that of the single relational
  column and the relational table.
• Data in a relational database can be categorized
  by its purpose.
• Referential data
• Columns that are commonly indexed
• Other descriptive data
• Computed Columns With computed columns you can
  selectively index a Java attribute or operation.

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Sybase DataWindow/Datastore Technology

• Another approach is to use Sybases DataWindow
  technology to bridge the object/relational gap
• This is particularly useful for less capable
  databases or legacy databases, or when
  organizations have PowerBuilder or PowerJ
  developers.
• Approach
• Replace class attributes with a single DataStore
  or DataWindow class variable
• Create Operations to manipulate classes
• Create DataWindow Objects for the database tables
• Use native DataWindow/DataStore Class methods to
  access relational data

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So Where do I Start?

• If you are beginning a new design, you will want
  to start in the OOM, or perhaps the CDM if you
  are less technical
• If you are reverse engineering a database, you
  will start in the PDM and reverse the PDM to the
  OOM or CDM
• If you are reverse engineering a PowerBuilder or
  Java application, you will start in the OOM

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