OBJECTS

1
OBJECTS

• Object Oriented ???????

2
OBJECTS
3
Object-Oriented

• OO convenient label for a collection of
  interconnected ideas
• OO approach views computer system as a collection
  of interacting objects
• Objects viewed as things
• things interact
• people interact with things
• Need to know what an object does
• Component approach

4
Object-oriented Approach

• Object-oriented analysis
• defining all of the types of objects that are
  part of a users work environment
• Object-oriented design
• define all the types of objects in computer
  system and how they interact
• UML
• Object-oriented programming
• programmers write statements that define types of
  objects
• C, JAVA, Small Talk

5
Object-oriented Approach cont

• Object databases - ultimate management system for
  multimedia, documents and other info.
• Object brokers (Agents) - in distributed systems,
  allow objects to dynamically discover each other
  and interact across machines and through the web
• Object frameworks - provide flexible,
  customizable, prefabricated software subsystems.

6
OO??

• Object Orientation - a set of design and
  development principles based on the idea of
  conceptually autonomous structures. Each
  autonomous structure represents a real world
  user's entity with the ability to interact with
  itself and other objects.
• Object - an abstract representation of a real
  world entity that has a unique identity, embedded
  properties, and the ability to interact with
  other objects and itself.
• Class - collection of similar objects with shared
  attributes and methods.

7
Core Model

• Class
• Object belongs to only one class
• is an instance of the class
• provides the basis for queries
• Class Hierarchy and Inheritance
• single inheritance -hierarchy
• multiple inheritance- rooted and connected
  directed acyclic graph (DAG)

8
Core Model

• Object Identifier
• unique
• system-wide
• Attributes
• value of attribute also object
• domain is a class of attribute values
• Encapsulation and Message Passing

9
Object-oriented concepts

• Abstraction, encapsulation, information hiding.
• Objects and attributes.
• Object identity.
• Methods and messages.
• Classes, subclasses, superclasses, and
  inheritance.
• Overloading.
• Polymorphism and dynamic binding.

10
(No Transcript)
11
Comparison between Rel DB Obj DB

• relations which are sets of tuples
• Tuple components primitive types
• Persistence
• Backup Recovery
• Transactions
• Concurrency
• Security Integrity
• Administration

• classes which are sets of objects
• Object components complex types
• Inheritance hierarchy
• Methods
• Methods integral part of class and inherited
• DML and host language can be the same

12
Weaknesses of RDBMSs

• Poor Representation of "Real World" Entities
• Normalization leads to relations that do not
  correspond to entities in "real world".
• Semantic Overloading
• Relational model has only one construct for
  representing data and data relationships the
  relation.
• Relational model is semantically overloaded.

13
Weaknesses of RDBMSs

• Poor Support for Integrity and Enterprise
  Constraints
• Homogeneous Data Structure
• Relational model assumes both horizontal and
  vertical homogeneity.
• Many RDBMSs now allow Binary Large Objects
  (BLOBs).

14
Weaknesses of RDBMSs

• Limited Operations
• RDBMs only have a fixed set of operations which
  cannot be extended.
• Difficulty Handling Recursive Queries
• Extremely difficult to produce recursive queries.
• Extension proposed to relational algebra to
  handle this type of query is unary transitive
  (recursive) closure, operation.

15
Weaknesses of RDBMSs

• Limited Operations
• RDBMs only have a fixed set of operations which
  cannot be extended.
• Difficulty Handling Recursive Queries
• Extremely difficult to produce recursive queries.
• Extension proposed to relational algebra to
  handle this type of query is unary transitive
  (recursive) closure, operation.

16
Weaknesses of RDBMSs

• Other Problems with RDBMSs
• Transactions are generally short-lived and
  concurrency control protocols not suited for
  long-lived transactions.
• Schema changes are difficult.
• RDBMSs are poor at navigational access.

17
BENEFITS OF OODBMS

• More semantic informatiom
• Multimedia, CAD, CAM
• User defined data types
• Versioning
• Class Reusability
• Faster development (inheritance, reusability)
• Portability

18
DRAWBACKS TO OODBMS

• Still developing
• Lack of standards
• Is there a sufficient theoretical foundation?
• Is this a throwback to hierarchical systems
• No ad hoc query language
• No set of tools
• Steep learning curve

19
CURRENT DATABASE FEATURES

• Language
• DDL
• DML
• DCL
• Concurrency Control
• Recovery
• Utilities

20
13 Rules for an OODBMSfrom the OODBS Manifesto

• System must support complex objects
• Object identifier must be supported
• Objects must be encapsulated
• Systems must support types or classes
• System must support inheritance
• System must avoid premature binding
• System must be computationally complete

21
LAST 6 RULES

• System must be extensible
• System must be able to remember data locations
• System must be able to handle very large
  databases
• System must support concurrent users
• System must be able to recover from hardware and
  software
• Data query must be simple

22
Key Tensions

• Two data models needed
• object model (data programs) vs. relational
  model (data constraints)
• Must one model dominate? Are they built
  simultaneously?
• relational model needs some object features
• Impedance mismatch
• object-at-a-time navigation vs. set-at-a-time
  queries
• programmatic vs. declarative integrity
  enforcement
• Concurrency discordance
• single image vs. shared database mindset
• Interoperability
• what other applications must use database?

23
Commercial OODBMSs

• GemStone from Gemstone Systems Inc.,
• Itasca from Ibex Knowledge Systems SA,
• Objectivity/DB from Objectivity Inc.,
• ObjectStore from eXcelon Corp.,
• Ontos from Ontos Inc.,
• Poet from Poet Software Corp.,
• Jasmine from Computer Associates/Fujitsu,
• Versant from Versant Object Technology.

24
NEXT GENERATION DB SYSTEMS NEED THE ABILITY TO

• represent and manipulate complex nested objects
• store and retrieve long data
• define and manipulate arbitrary data types
• represent and manage changes over time (versions)
• represent semantic modeling concepts
• specify rules and extended constraints
• manage long-duration cooperative transactions

25
Relationships

• Relationships represented using reference
  attributes, typically implemented using OIDs.
• Consider how to represent following binary
  relationships according to their cardinality
• 11
• 1
• .

26
11 Relationship Between Objects A and B Add
reference attribute to A and, to maintain
referential integrity, reference attribute to B.
27
1 Relationship Between Objects A and B

• Add reference attribute to B and attribute
  containing set of references to A.

28
Relationship Between Objects A and B

• Add attribute containing set of references to
  each object.
• For relational database design, would decompose
  N into two 1 relationships linked by
  intermediate entity. Can also represent this
  model in an ODBMS.

29
Relationships
30
Alternative Design for Relationships