Transcript DBMS

Basic DB Terms
• Data: Meaningful facts, text, graphics, images, sound,
video segments
– A collection of individual responses from a marketing research
• Information: Data processed to be useful in decision
making
– Pattern of geographical buying habit based on analysis of a
marketing research
• Metadata: Data that describes data
1
Data in Context
Large volume of facts, difficult to interpret / make decisions
2
Information
Useful for decision making / interpretation
3
Metadata
Descriptions of the properties or characteristics of the
data, including data types, field sizes, allowable values,
and documentation (Data Dictionary)
4
Database
• Collection of data in electronic format
– A digital library of organization
 Managed by one set of software that provides access to all
the data
– No data redundancy, data inconsistency, poor security, applicationdata dependency...
5
Database Systems
Application
#1
Application
#2
DBMS
Database
containing
centralized
shared data
Application
#3
6
Database Management System
(DBMS)
• Database software
• Act as an interface between application and physical data
files
• Support centralization of data
• Independent of specific computer programs
• small (MS Access), large/popular (Oracle)
7
Database Models
• Hierarchical (Tree) Models
• Network Model
• Relational Models
8
Hierarchical database Model
• Logically represented by an upside down tree
– Each parent can have many children
– Each child has only one parent
9
Hierarchical Database
Hierarchical Database
A schematic diagram of a hierarchical database (a) and a sample part of a
hierarchical database showing relationships among different records (b)
11
Network Database Model
• Each record can have multiple parents
– Composed of sets
– Each set has owner record and member record
– Member may have several owners
12
Network Database
Network Database
A schematic diagram of a network database (a) and a sample of part of a network
database showing relationships among different records (b)
14
Relational Database Model
• A group of related tables
• Introduced in 1970 by E. F. Codd of IBM
• The most popular model.
– Mathematical simplicity
– Ease of visualization
15
Relational Database
A schematic diagram of a relational database (a) and a sample part of a
relational database showing different tables (b)
16
Relational database and keys
• A relational database is a collection of tables that are
related to one another based on a common field.
• A field, or a collection of fields, is designated as the
primary key.
– The primary key uniquely identifies a record in the table.
• When the primary key of one table is represented in a
second table to form a relationship, it is called a foreign
key.
17
Relating tables using a common field
The primary key in the
Employer table (EmployerID) is
the common field that relates
this table to the Position table.
PositionID is the primary key in
the Position table. The EmployerID
field is a foreign key in this table.
Primary keys can only have one
occurrence in a table. Foreign keys
may have multiple occurrences.
18
Primary Key
• Unique identifiernt
– Last name vs. SS#
• Prevent confusion
• Cost of PK
– SS# vs. finger print
– Entity Integrity Rule
– Any primary key is allowed to accept null values.
19
Foreign Key
• An attribute in one table whose values must either match
the primary key in another table or be null.
• The database must not contain any unmatched foreign key
values.
20
Figure 2
21
Referential Integrity Rule
• Cascade Update Related Fields
– Change of PK values in primary table  automatic change of FK
values
• Cascade Delete Related Fields
– Delete of a record in the primary table  automatic delete of all
records in the related table that have a matching FK value
• See example from the class web site
– Primary table: customer
22
Relational Database Model
• Advantages
– Easier database design, implementation, management, and use
– Ad hoc query capability with SQL
– Powerful database management system
23
DATABASE MODEL
Hierarchical
Network
Relational
Object-Relational
PRODUCT
Focus
IMS
Ramis
ADABAS
Image
Access
DB2
dBASE V
EDA/SQL
FoxPro
Ingres
NOMAD
Oracle
Paradox
Rbase
SQL/DS
SQL Server
Sybase
ObjectStore
Universal
Server
Illustra
VENDOR
Information Builders International
IBM
Online Software International
Software AG of North America
Hewlett-Packard
Microsoft
IBM
Borland International
Information Builders International
Microsoft
Ask Group
Must Software International
Oracle
Borland International
Microrim
IBM
Microsoft
Sybase
Object Design
Informix
HARDWARE
Mainframe/PC
Mainframe
Mainframe
Mainframe
Mainframe
PC
Mainframe
PC
PC
PC
PC
Mainframe/PC
Mainframe/PC
PC
PC
Mainframe
PC
PC
PC
PC
Informix
PC
24
Basic Components of DBMS
• Data dictionary
• DDL (Data Definition Language)
• DML (Data Manipulation Language)
25
The Data Dictionary (Metadata)
- description of every piece of data in database
- Maintains all information supplied by the developer when
schema
constructing the
A typical data dictionary for a staff file
26
• Data Definition Language (DDL)
– language to create and modify data
– Access table with data type, description, and field properties
Data definition language to create a schema in NOMAD
27
• Data Manipulation Language (DML)
– language that process, update, and retrieve data
– Access query
A Paradox query by example
28
Structured Query Language (SQL)
• Standard Query Language (SQL) is the relational model’s
standard language.
• Another way to generate queries
– MS Access: queries by QBE
– Other DBMSs: queries by SQL
29
Example of SQL
• You want to see the address of each employee: FirstName, LastName,
Address, City, and State
EmployeeAddressTable
SSN
FirstName LastName Address
City
State
Ohio
512687458 Joe
Smith
83 First Street
Howard
758420012 Mary
Scott
842 Vine Ave.
Losantiville Ohio
102254896 Sam
Jones
33 Elm St.
Paris
New York
876512563 Sarah
Ackerman
440 U.S. 110
Upton
Michigan
30
Example of SQL
• SELECT FirstName, LastName, Address, City, State
FROM EmployeeAddressTable;
First Name
Last Name
Address
City
State
Joe
Smith
83 First Street
Howard
Ohio
Mary
Scott
842 Vine Ave.
Losantiville
Ohio
Sam
Jones
33 Elm St.
Paris
New York
Sarah
Ackerman
440 U.S. 110
Upton
Michigan
SQL tutorial: w3.one.net/~jhoffman/sqltut.htm
31
Database Design Process
Problem
Domain
Conceptual Design
Conceptual Schema
Logical Design
Logical Schema
Physical Design
Physical Schema
32
Conceptual Design
• The conceptual design is a high level description of the
structure of the database, independent of the particular
DBMS software that will be used to implement the database.
• The conceptual design revolves around discovering and
analyzing organizational and users data requirements.
– What data is important
– What data should be maintained
• The major activity of this phase is constructing a data model
(Entity-Relationship Diagram).
33
Data Model: Entity-Relationship Diagram
Why Conceptual Modeling is Important?
• Effective Communication Tool
• User involvement
• Independence from a particular DBMS
• Documentation
35
Logical Design
• The logical design is a description of the structure of the
database that can be processed by the DBMS software. In
other words, the logical design adapts the conceptual design
to a specific DBMS implementation model
• Thus, the logical design is software-dependent.
• Logical Models
– Relational Model
– Network Model
– Hierarchical Model
36
Physical Design
• The physical design describes the storage structures and
data access methods used in system. In other words, the
physical design is a description of the implementation of
the database in secondary memory.
37