24-09-2012, 03:36 PM
DATABASE CONCEPTS
databaseconcepts.ppt (Size: 545 KB / Downloads: 293)
What a Database Is and Is Not
your personal address book in a Word document
a collection of Word documents
a collection of Excel Spreadsheets
a very large flat file on which you run some statistical analysis functions
data collected, maintained, and used in airline reservation
data used to support the launch of a space shuttle
Models of Reality
A database is a model of structures of reality
The use of a database reflect processes of reality
A database system is a software system which supports the definition and use of a database
DDL: Data Definition Language
DML: Data Manipulation Language
Why Use Models?
Models can be useful when we want to examine or manage part of the real world
The costs of using a model are often considerably lower than the costs of using or experimenting with the real world itself
Examples:
airplane simulator
nuclear power plant simulator
flood warning system
model of US economy
model of a heat reservoir
map
A Message to Map Makers
A model is a means of communication
Users of a model must have a certain amount of knowledge in common
A model on emphasized selected aspects
A model is described in some language
A model can be erroneous
A message to map makers: “Highways are not painted red, rivers don’t have county lines running down the middle, and you can’t see contour lines on a mountain” [Kent 78]
Process Modeling
The use of the model reflects processes of reality
Processes may be represented by programs with embedded database queries and updates
Processes may be represented by ad-hoc database queries and updates at run-time
Database Design
is a model of structures of reality
supports queries and updates modeling processes of reality
runs efficiently
Object-Oriented Paradigm
object class
object attributes, primitive types, values
object interface, methods; body, implementations
messages; invoke methods; give method name and parameters; return a value
encapsulation
visible and hidden attributes and methods
object instance; object constructor & destructor
object identifier, immutable
complex objects; multimedia objects; extensible type system
subclasses; inheritance; multiple inheritance
operator overloading
references represent relationships
transient & persistent objects