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What is a database
What is a Database
--What is a Database--
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Basic Difinitions
 Miniworld: Some part of the real world about which
information is stored.
 Data: Known facts about the miniworld
 recorded
 have an implicit meaning
 Database (DB): A collection of related data elements
 Database Management System (DBMS): A software
package to facilitate the process of




Defining - specifying types, organization (schema)
Constructing - loading the data
Manipulating - querying the data
One DBMS, many DBs, many applications
 Database system: A database and a DBMS
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A DBMS
application program
DBMS
user
database
database
persistent storage
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Pictorial Representation
Users/Programs
DATABASE
SYSTEM
Application Programs/Queries
DBMS
SOFTWARE
Software to Process
Queries/Programs
Software to Access
Stored Data
Stored Database
Definition
(Meta-Data)
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Stored
Database
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Functions of a DBMS
 Provides persistent, shared storage
 Objects live beyond program execution
 Shared by multiple applications
 DBMS reduces redundancy in Development and maintenance
 Provides multiple interfaces
 Query language, embedded query language, APIs, GUIs
 Protects against
 Software/hardware failure
 Security breaches
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When not to use a DBMS
 Main costs of using a DBMS




High initial investment
May need additional hardware
Overhead
Training
 When a DBMS may be unnecessary
 Application is simple, well-defined, and not expected to change
 Stringent real-time requirements
 (Write) access to data by multiple users is not needed
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Classes of DB users – Workers on the scene
 Persons whose job involves daily use of a large database.
 Database administrators (DBAs)
 Responsible for managing the database system.
 Database designers
 End users
 The people that use the database for querying, updating, generating
reports
 Interactive users: Use full DBMS capabilities directly via a DML.
 Parametric (or naive) end users: They use pre-programmed canned
transactions to interact continuously with the database. For example,
bank tellers or reservation clerks.
 Application programmers
 Design and implement canned transactions for parametric users.
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DBA Duties
 Chooses
 storage structure and access strategy
 performance-enhancing data structures
 Acts as liaison with users
 Security czar
 Defines authorization checks and validation procedures
 Responsible for
 backups and recovery
 monitoring performance and updates (to schema)
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Database Users – Workers Behind the Scene
 People who design and develop the DBMS software
 DBMS designers and implementers
 Tool developers
 Design and implement tools that facilitate the use of DBMS
software. Tools include design tools, performance tools, special
interfaces, etc.
 Operators and maintenance personnel
 Run and maintain the hardware and software environment for
the database system.
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Interfaces
 Menu vs. form-based
 GUI
 Canned interfaces for parametric users
 DBA
 Application
 Natural language
 Web search engines
 Shell
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Input (Using a Form)
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Sample of Input Form for a Lab Work
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Output (Using a Report)
Exam result for ID
SID
Name
1’st
2’nd
3’rd
Total
8891
Allen
25%
27%
33%
85%
8767
Jones
20%
25%
0
45%
2365
Watson
13%
0
0
13%
4256
Cabeen
15%
20%
17%
52%
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Sample Output Report for a Lab Work
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Data Models
 A data model is a data definition language along with a
data manipulation language.
 Conceptual
 Representational
 Physical
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Data Models
 A data definition language (DDL) describes database
schemas.
 Data relationships
 Data semantics
 Integrity constraints
 Database schemas vs. instances
 Similar to types and variables in programming languages
 A data manipulation language (DML) is used for
querying and updating database instances.
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Schema vs. Instance
 Schema - Description of how data is organized and
constrained.
 Instance - The data in a database (conforms to a
schema).
 Snapshot - Database state at a particular point in time.
 Initially empty
 Database is populated or loaded, DBMS ensures every state is a
valid state.
 Schema evolution vs. data update
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Type of Data Models
 Record-based conceptual models
 (1960s) hierarchical model (e.g., IBM IMS)
 (1970s) network model (e.g., CA-IDMS)
 (1980s - current) relational model (e.g., Microsoft Access,
Microsoft SQL Server, IBM DB2, Oracle8)
 Object-based conceptual models
 (late 1980s - current) entity-relationship model
 §(late 1980s - current) object-oriented model
 Text-based conceptual models
 (late 1990s - current) XML
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ANSI Three-Schema Architecture
 Supports DBMS characteristics of:
 Program-data independence.
 Support of multiple views of the data.
 Defines DBMS schemas at three levels:
 Physical
 How data is stored on disk
 Data storage structures
 Access paths to the data
 Logical
 External
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Schema and Mappings
external level
First Name Last Name
conceptual level
physical level
Salary
StaffID Name
Birthdate
staff_no fname lname dob branch_no salary
Struct STAFF {
int staff_no;
int branch_no;
char fname [15];
char lname [15];
struct date dob;
float salary;
struct STAFF *next;
};
index staff_no; index branch_no;
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Data Independence
 Each level is “independent” in the sense that a
completely different organization can be used.
 Physical data independence - Physical level can change
without having to change the logical level.
 Logical data independence - Logical level can change
without having to change the external level.
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DBMS Achitecture
Application Programmers
DBA Staff
DDL
Statements
Privileged
Commands
Casual Users
Application
Programs
Interactive
Query
Precompiler
Parametric
Users
Host Language
Compiler
Query
Compiler
DDL
Compiler
Query Execution
Plan
Canned
Transactions
DML
Statements
Run-time
Evaluator
DBMS
Transaction and
Data Manager
Data Dictionary
Data Files
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