OO RDBMS

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OO ? RDBMS
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Database Management Systems

• Permanent self-descriptive repository of data
• Motivations
• Crash recovery
• Sharing between users
• Sharing between applications
• Security
• Integrity
• Extensibility
• Data distribution

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Three Schema Architecture
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Relational Database Concepts 1

• Data represented as tables
• Specific number of columns (attributes)
• Arbitrary number of rows (tuples)
• Operators
• SQL set oriented
• View
• Virtual table that is dynamically computed as
  needed

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Relational Database Concepts 2

• Integrity
• Entity integrity
• Each table has exactly 1 primary key (combination
  of 1 or more attributes whose value unambiguously
  locates each row in a table)
• Referential integrity
• Each foreign key (primary key of 1 table embedded
  in another table) kept consistent with primary
  key
• Normal forms
• Rules developed to avoid logical inconsistencies
  from table update operations

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Extended 3 Schema Architecture for Object Models
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Object Ids

• Possible to assign a unique id to each tuple in a
  table
• Advantage
• Independent of changes in data physical
  location
• Disadvantages
• Undermines RDBMS theory that says that data
  should be located manipulated based strictly on
  its attribute values

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Mapping Classes to Tables

• Each class maps to 1 or more tables
• Objects in class may be partitioned
  horizontally (use multiple tables separation
  based on efficiency) or verically (writing 1
  tuple as multiple tuples)

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Horizontal Partitioning
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Vertical Partitioning
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Mapping Binary Associations to Tables 1

• Association may or may not map to a table
• Many-to-many associations
• Always map to a distinct table (satisfy third
  normal form)
• Primary keys for both classes any link
  attributes become attributes of this new table

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One to Many Associations 1

• Distinct table for each association

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One to Many Associations 2

• Bury foreign key in table for many class
• Advantages
• Fewer tables
• Better performance
• Disadvantages
• Lose design concept of an association
• More complexity
• Reduced reusability

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One to Many Associations 3

• Collapse both classes association into a single
  table
• Least desirable alternative

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One to One Associations

• Same alternatives as 1 - many

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Mapping Generalizations to Tables

• Each class own table
• Add field to parent class to denote which child
• Each child class contains primary key of parent
• Table for each child class
• Copy attributes of parent class to each child
  class
• One table for parent children
• Each record only uses pertinent attributes

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