Transcript No Slide Title - Computer Information Systems

OBJECTS
Object Oriented ???????
OBJECTS
Does the relational model meet the needs
of the 21st Century?
Can the world be modeled better through
objects?
What are objects?
Where does object oriented ??? fit into the
IS world?
Should I get rid of all my tables and
convert?
Object-Oriented
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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
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Need to know what an object does
Component approach
Object-oriented Approach
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Object-oriented analysis
– defining all of the types of objects that are part of a
users work environment
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Object-oriented design
– define all the types of objects in computer system
and how they interact
– UML
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Object-oriented programming
– programmers write statements that define types of
objects
– C++, JAVA, Small Talk
Object-oriented Approach con’t
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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.
OO??
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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.
Core Model
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Class
– Object belongs to only one class
– is an instance of the class
– provides the basis for queries
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Class Hierarchy and Inheritance
– single inheritance -hierarchy
– multiple inheritance- rooted and connected
directed acyclic graph (DAG)
Core Model
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Object Identifier
– unique
– system-wide
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Attributes
– value of attribute also object
– domain is a class of attribute values
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Encapsulation and Message Passing
Object-oriented concepts
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Abstraction, encapsulation,
information hiding.
Objects and attributes.
Object identity.
Methods and messages.
Classes, subclasses, superclasses,
and inheritance.
Overloading.
Polymorphism and dynamic binding.
O
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Object Oriented
Features
OODBMS
Conventional
DBMS Features
Comparison between
Rel DB
Obj DB
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relations which are
sets of tuples
Tuple components
primitive types
Persistence
Backup & Recovery
Transactions
Concurrency
Security & Integrity
Administration
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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
Weaknesses of RDBMSs
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Poor Representation of "Real World"
Entities
– Normalization leads to relations that do
not correspond to entities in "real world".
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Semantic Overloading
– Relational model has only one construct
for
representing
data
and
data
relationships: the relation.
– Relational
model
is
semantically
overloaded.
Weaknesses of RDBMSs
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Poor Support for Integrity
Enterprise Constraints
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Homogeneous Data Structure
and
– Relational
model
assumes
both
horizontal and vertical homogeneity.
– Many RDBMSs now allow Binary Large
Objects (BLOBs).
Weaknesses of RDBMSs
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Limited Operations
– RDBMs only have a fixed set of
operations which cannot be extended.
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Difficulty
Queries
Handling
Recursive
– Extremely
difficult
to
produce
recursive queries.
– Extension proposed to relational
algebra to handle this type of query is
unary transitive (recursive) closure,
operation.
Weaknesses of RDBMSs
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Limited Operations
– RDBMs only have a fixed set of
operations which cannot be extended.
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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.
Weaknesses of RDBMSs
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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.
BENEFITS OF OODBMS
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More semantic informatiom
Multimedia, CAD, CAM
User defined data types
Versioning
Class Reusability
Faster development (inheritance,
reusability)
Portability
DRAWBACKS TO OODBMS
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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
CURRENT DATABASE
FEATURES
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Language
– DDL
– DML
– DCL
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Concurrency Control
Recovery
Utilities
13 Rules for an OODBMS
from the OODBS Manifesto
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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
LAST 6 RULES
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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
Key Tensions
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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
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Impedance mismatch
– object-at-a-time navigation vs. set-at-a-time queries
– programmatic vs. declarative integrity enforcement
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Concurrency discordance
– single image vs. shared database mindset
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Interoperability
– what other applications must use database?
Commercial OODBMSs
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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.
NEXT GENERATION DB
SYSTEMS NEED THE
ABILITY TO:
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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
Relationships
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Relationships represented using
reference attributes, typically
implemented using OIDs.
Consider how to represent following
binary relationships according to their
cardinality:
– 1:1
– 1:*
– *:*.
1:1 Relationship Between Objects A and B
Add reference attribute to A and, to maintain
referential integrity, reference attribute to B.
1:* Relationship Between Objects A and B
Add
reference attribute to B and attribute
containing set of references to A.
*:*
Relationship
Objects A and B
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Between
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.
*:* Relationships
Alternative Design for *:* Relationships