CS311 Database Management system Somchai Thangsathityangkul 1.
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CS311 Database Management system
Somchai Thangsathityangkul
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Database Systems
Database system consists of logically related data stored in a single logical data repository May be physically distributed among
multiple storage facilities DBMS eliminates most of file system’s
problems
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The Database System Environment
Five major parts of a database system: Hardware Software People Procedures Data
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The Database System Environment (cont'd.)
Hardware: all the system’s physical devices
Software: three types of software required: Operating system software DBMS software Application programs and utility
software
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The Database System Environment (cont'd.)
People: all users of the database system System and database administrators
Database designers
Systems analysts and programmers
End users
Procedures: instructions and rules that govern the design and use of the database system
Data: the collection of facts stored in the database
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Data Models
Data models Relatively simple
representations of complex real-world data structures Often graphical
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Data Model Basic Building Blocks
Entity: anything about which data are to be collected and stored
Attribute: a characteristic of an entity Relationship: describes an association
among entities One-to-many (1:M) relationship
Many-to-many (M:N or M:M) relationship
One-to-one (1:1) relationship
Constraint: a restriction placed on the data
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One to One Relationship
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One to Many Many to Many
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Business Rules
Descriptions of policies, procedures, or principles within a specific organization Apply to any organization that stores and uses
data to generate information
Description of operations to create/enforce actions within an organization’s environment Must be in writing and kept up to date
Must be easy to understand and widely disseminated
Describe characteristics of data as viewed by the company
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The Relational Model
Developed by E.F. Codd (IBM) in 1970 Table (relations)
Matrix consisting of row/column intersections
Each row in a relation is called a tuple
Relational models were considered impractical in 1970
Model was conceptually simple at expense of computer overhead
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The Relational Model (cont’d.)
Relational diagram Representation of entities,
attributes, and relationships
Relational table stores collection of related entities
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15 The Relational Model
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The Entity Relationship Model
Widely accepted standard for data modeling
Introduced by Chen in 1976 Graphical representation of entities and
their relationships in a database structure
Entity relationship diagram (ERD) Uses graphic representations to model
database components Entity is mapped to a relational table
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The Entity Relationship Model (cont’d.)
Entity instance (or occurrence) is row in table Entity set is collection of like entities Connectivity labels types of relationships Relationships are expressed using Chen
notation Relationships are represented by a diamond
Relationship name is written inside the diamond
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Entities and Instances
PERSON
PRODUCT
PRODUCT TYPE
EMPLOYMENT CONTRACT
JOB
SKILL LEVEL
TICKET RESERVATION
PURCHASE
ELECTION
PRINTER PREFERENCE
DOCUMENT VERSION
Mahatma Gandhi2.5 x 35 mm copper nailnailmy previous contractviolinistfluenttonight: Hamlet in the Royalthe CD I bought yesterdayfor parliament next fall…...
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Entities and Sets
An entity represents a set of instances that are of interest to a particular business.
dish washer
waiter
cookwaitress
manager
financial controller
porter
piano player
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Relationship
JOB
waiter
cook
waitress
manager
financial controller
porter
piano player
Ahmed
JillAdam
Maria
EMPLOYEE
Shintarodish washer
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The Entity Relationship Model21
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Degrees of Data Abstraction
Database designer starts with abstracted view, then adds details
ANSI Standards Planning and Requirements Committee (SPARC) Defined a framework for data modeling
based on degrees of data abstraction (1970s): External
Conceptual
Internal
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Degrees of Data Abstraction23
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The External Model
End users’ view of the data environment
ER diagrams represent external views External schema: specific
representation of an external view Entities Relationships
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The Conceptual Model
Represents global view of the entire database
All external views integrated into single global view: conceptual schema
ER model most widely used ERD graphically represents the
conceptual schema
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The Conceptual Model27
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The Internal Model
Representation of the database as “seen” by the DBMS Maps the conceptual model to the DBMS
Internal schema depicts a specific representation of an internal model
Depends on specific database software Change in DBMS software requires internal
model be changed
Logical independence: change internal model without affecting conceptual model
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The Internal Model29
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The Physical Model
Operates at lowest level of abstraction Describes the way data are saved on storage
media such as disks or tapes
Requires the definition of physical storage and data access methods
Relational model aimed at logical level Does not require physical-level details
Physical independence: changes in physical model do not affect internal model
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