© InfoGem Introduction to Database Database system is a computer based record keeping system. It is a system whose overall purpose is to record and maintain information. The information concerned can be anything that is deemed important to the organization. In another words, database is collection of stored operational data which can be used and shared by different applications and users of any enterprise. This enterprise could be scientific, commercail, educational, etc.
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Introduction to Database
Database system is a computer based record keeping system.
It is a system whose overall purpose is to record and maintain information. The information concerned can be anything that is deemed important to the organization.
In another words, database is collection of stored operational data which can be used and shared by different applications and users of any enterprise. This enterprise could be scientific, commercail, educational, etc.
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Why Database
Database system provides the enterprise with centralized control of its operational data, which is one of its most valuable assets.
This is totally oposite of the situation that is happening in many organizations today, where typically each application has its own private files and a lot of times its own private tapes and disk packs too. This makes the operational data widely dispered and difficult to control.
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Advantage of centralized database
Redundancy can be reduced Inconsistency can be avoided Data can be shared Standards can be enfored Security restrictions can be applied Integrity can be maintained Conflicting requirements can be balanced
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Data independence Data indepencence is an objective in database development Most present day applications are data dependent. This is
the way in which the data is organized in secondary storage and is accessed. Both are dictated by the requirements of the application. This is undesirable because:
» Different applications will need defferent view of the same data.
» Data Base Adminstrator (DBA) must have the freedom to change the storage structure or access strategy or both in response to changing requirements without the necessity of modifying existing application.
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Data independence
Data independence could be defined as that, applications concerned with data, not depend on storage structure or access strategy of data.
With data independence database is able to grow without affecting existing applications (another major reason).
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ANSI database system architecture
External Level
. . .
Conceptual LevelCmmunity user view
External Level(Individual user view)
Internal Level(phisical storage view
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ANSI database system architecture
External Level
. . .
Conceptual LevelCmmunity user view
External Level(Individual user view)
Internal Level(phisical storage view
A1 A2 A3 An
mapping External/conceptual
mapping conceptual/internal
DatabaseManagementSystem(DBMS)
DataDictionary
Conceptual Schema
ExternalSchema
ExternalSchema
Internal schema
DBA
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Database architecture-terms
Schema: defines a database and sub-schema defines a portion of the database.
Schema and mapping built and maintained by the database adminstrator.
Conceptual schema is known as data model Internal level is concerned with the in which the
data is actually stored. Users are:
» application programmers» ad hoc users» external users
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Database architecture-terms
Each user communicates with the database via a language referred as data sub-language (DSL), which is the subset of the language concerned with the retrieval and storage of information in the database.
Mapping defines the correspondence between data models and external/internal schema.
DBMS is the software that handles all access to the database and also is responsible for applying the authorization checks and validation procedures.
DBMS is a bridge between users and data.
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Data Base Adminstrator DBA is responsible for supervising the overall DBS. DBA’s responsibilities:
» Deceiding the information content of the DBS
» Decide about the storage structure and access strategy
» Interface between users and DBS:
– Insure the availability of data for users
– Assist users for their inquiries
– In cooperation with users set up the external schema
» Define authorization check and validation procedures.
» Define the strategy for back up and recovry process.
» monitoring the performance and respond to changing requirements.
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Data Dictionary
Data dictionary is the most important tool for DBA. Data dictionary is a database on its own right. It defines all data and their relationship, “ data anot
data” or information about meta data.
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Disadvantage of Database Systems
Database is more vulnerble to destruction thru:» machine malfunction» personal error» Deliberate human tampring
Cost: the cost of required hardware, DB development, and DB maintenance is high.
Complexity: Due to its complexity, the user should understand it well enough to use it effecienty and effectively.
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Database models
Almost all of the database systems developed over the past two decades are relational.
Almost all of the database research is also based on relational related ideas.
Relational database is a system in which:» the data is perseived by the user as tables» the operators at user’s disposal are operators which
generate a new table from old We can categorize systems by the data
structures and operators they present to the users.
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Database Models - Product - Vendor
The four major data model categories are:» Relational DB2 IBMSQL/DS
Ingress Relational Technology
Oracle Oracle corp.
Access Microsoft » Network DMS100 Unysis
IDMS Cullinet» Heirarchical IMS IBM
System 2000 Intel» Object oriented Postgress Relational Technology
Starburst IBM
Gemstone
Orion
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Relational Database
Relational database is a collection of tables Formally a table is called a relation Database is a structure that can hold
information about tables, rows, and columns
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Relational Database
Relational Relational Traditional
Model DBMS File System
Relation Table File
Tuple Row Record
Attribute Column Field
Primary Key (PK) Primary Key (PK) Search Key
Relationship (FK) Relationship (FK) Not Used
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Relational Database
Primary Key (PK): An attribute which can uniquely identify each record (tuple) of a relation (table).
Foreign Key (FK): An attribute which is a regular attribute in one table but a primary key in another table.
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Example of a Relational
Database
SalesNO Name Rate City Dept#
10 James 10 Dallas A21112 Black 15 Denver F65448 Black 8 WashDC A211
SalePrimary Key (PK)
Relation Name
Tuple (record)
Attribute
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SalesNO Name Rate City Dept#
10 James 10 Dallas A21112 Black 15 Denver F65448 Black 8 WashDC A211
Sale
CustID Name Balance City SaleNo
132 Black 2000.00 Dallas 10135 Tom 129.89 Denver 12198 Tom (132.90) Dallas 10
Customer
SalesNO is PK in Sales table
Example of a Relational Database
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SalesNO Name Rate City Dept#
10 James 10 Dallas A21112 Black 15 Denver F65448 Black 8 WashDC A211
Sale
CustID Name Balance City SaleNo
132 Black 2000.00 Dallas 10135 Tom 129.89 Denver 12198 Tom (132.90) Dallas 10
Customer
SalesNO is PK in Sales table and FK in Customer table
Example of a Relational Database
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OrderLine
ONO Oline# Part# Qty Part#
102 1 12.00 10 EX454102 2 129.89 1 DE012199 1 32.90 3 DC810
ONO DATE CustID SalesNO
102 11/2/94 132 10199 2/15/95 135 12 92 10/4/94 102 53
Order
CustID Name Balance City SaleNo
132 Black 2000.00 Dallas 10135 Tom 129.89 Denver 12198 Tom (132.90) Dallas 10
Customer
SalesNO Name Rate City Dept#
10 James 10 Dallas A21112 Black 15 Denver F65448 Black 8 WashDC A211
Sale
Example: Order Entry Database
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