ObjectOriented Analysis

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Object-OrientedAnalysis Design

• Session 6

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Databases and DBMSs

• Databases are integrated collections of stored
  data that are centrally managed and controlled
• Described by a schema
• DBMSs are system software components that manage
  and control access to a database

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Components of a DB and DBMS
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DBMS Important capabilities

• Simultaneous access by multiple users and
  applications
• Access to data without application programs
• Managing organizational data

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Database Models

• Impacted by technology changes
• Model Types
• Hierarchical
• Network
• Relational
• Object-oriented
• Current systems generally use relational or
  object-oriented data models

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Relational Databases

• The relational database management system
  organizes data into tables or relations
• Tables
• Tuples rows or records
• Fields columns or attributes
• Tables have key field(s) which can be used to
  identify unique records
• Keys relate tables to each other

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Entity Relationship Diagram
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Partial Relational Database Table
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Designing Relational Databases

• Create table for each entity type
• Choose or invent primary key for each table
• Add foreign keys to represent one-to-many
  relationships
• Create new tables to represent many-to-many
  relationships
• Define referential integrity constraints
• Evaluate schema quality and make necessary
  improvements
• Choose appropriate data types and value
  restrictions (if necessary) for each field

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Enforcing Referential Integrity

• Consistent relational database state
• Every foreign key also exists as a primary key
  value
• DBMS enforces referential integrity automatically
  once schema designer identifies primary and
  foreign keys

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Automatic Enforcement for Referential Integrity

• When rows containing foreign keys are created,
  DBMS ensures that the value also exists as a
  primary key in related table
• When row is deleted, DBMS ensures no foreign key
  in related tables have the same value as primary
  key of deleted row
• When primary key value is changed, DBMS ensures
  no foreign key values in related tables contain
  the same value

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Evaluating Schema Quality

• High quality features
• Uniqueness of table rows and primary keys
• Ease of implementing future data model changes
  (flexibility and maintainability)
• Lack of redundant data
• Is Design judgment-based?

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Database Normalization

• Ensure database quality by minimizing data
  redundancy
• Normal forms
• 1NF - no repeating fields or groups of fields
• Functional dependency - one-to-one relationship
  between the values of two fields
• 2NF - in 1NF and if each non-key element is
  functionally dependent on entire primary key
• 3NF - in 2NF and if no non-key element is
  functionally dependent on any other non-key
  element

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Decomposition of 1NF Table into 2NF Tables
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Conversion of 2NF Table into 3NF Tables
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Object-Oriented Databases

• Direct extension of the OO design and programming
  paradigm
• ODBMS stores data as objects or classes
• Object definition language (ODL)
• Standard language for describing structure and
  content of an object database

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Designing Object Databases

• Determine which classes require persistent
  storage
• Define persistent classes
• Represent relationships among persistent classes
• Choose appropriate data types and value
  restrictions (if necessary) for each field.

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Representing Classes

• Transient
• Exist only during lifetime of program or process
• Examples view window, pop-up menu
• Persistent
• Not destroyed when program or process ceases
  execution
• Exist independently of program
• Examples customer information, employee
  information

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Representing Relationships

• Object identifiers
• Used to identify objects uniquely
• Physical storage address or reference
• Relate objects of one class to another
• ODBMS uses attributes containing object
  identifiers to find objects that are related to
  other objects

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Representing Relationships (cont.)

• Keyword relationship can be used to declare
  relationships between classes
• Advantages include
• ODBMS assumes responsibility for determining
  connection
• ODBMS assumes responsibility for maintaining
  referential integrity
• Type of relationships
• 11, 1M, MM
• Association class used with MM

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11 Relationship Represented with Attributes
Containing Object Identifiers
attributes shown in color
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1M Relationship Between Customer and Order
Classes
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1M with Attributes Containing Object Identifiers
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MM Relationship between Employee and Project
Classes
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MM Relationship Represented with two 1M
Relationships
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Generalization Hierarchy
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Hybrid Object-Relational Database Design

• Relational database management system used to
  store object attributes and relationships
• Two design tasks
• Developing complete relational schema
• Developing equivalent set of classes
• Problems
• Programmer defined method storage and execution
• Relationships are restricted
• ERDs cannot represent methods

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Relationships and Inheritance in Hybrid Design

• Relationships must be represented with foreign
  keys
• Inheritance
• Combine all tables into a single table containing
  a superset of all class attributes but excluding
  all invented fields from child classes
• Use separate tables to represent child classes
  and substitute the primary key of the parent for
  the invented keys of the child

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Data Types

• Storage format and allowable content of a program
  variable
• Primitive data types
• Pointer, Boolean, integer, etc.
• Complex data types
• Dates, times, audio streams, video images
• User-Defined data types

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Object DBMS Data Types

• Comparable to RDBMS data types
• Schema designer can create new data types and
  associated constraints
• Classes are complex user-defined data types that
  contain methods to manipulate data