DBMS, File Sys, Data Models[1]

8/4/2019 DBMS, File Sys, Data Models[1]

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Database Management Systems

versus

File System


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File Terminology

Data

Raw Facts

Field Group of characters with specific meaning

Record

Logically connected fields that describe a person,place, or thing

File and file folder

Collection of related records


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fieldrecord


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Simple File System

Figure 1.5


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File System

File System Data Management Requires extensive programming in third-generation

language (3GL): COBOL, Basic, and Fortran (whatmust be done and how it is to be done)

Time consuming

depends on physically store data

Makes ad hoc queries impossible Make difficult to modify file system (each file has its

own system)

Leads to islands of information


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Data Dependence

Change in files data characteristics requires

modification of data access programs Must tell program what to do and how to do

Structural Dependence

Change in file structure requires modification ofrelated programs

File System


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Field Definitions and Naming Conventions

Flexible record definition anticipates reporting

requirements

Selection of proper field names important

Attention to length of field names

Use of unique record identifiers

File System


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Data Redundancy

Different and conflicting versions of same data

Results of uncontrolled data redundancy Data anomalies

Modification

Insertion

Deletion Data inconsistency

Lack of data integrity

File System


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Database Systems

Database consists oflogicallyrelated datastored in a single repository

Provides advantages over file systemmanagement approach Eliminates data inconsistency (lack of data

integrity), data anomalies, data dependency, and

structural dependencyproblems Stores data structures, relationships, and access

paths


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Database vs. File Systems


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Database SystemEnvironment


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Hardware

Systems Physical devices

Computers Peripherals

Network


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Software

Operating system: manages hardware

components DBMS: manages database

MS Access, SQL Server, Oracle, DB2

Application and utility software:support access and manipulate data

Generate information for decision making

Help to manage database system


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People (five users)

System administrator : hardware systemsupport

Database administrator: manage DBMSuse

Database designer: design database

structure System analysts and programmers:

implement application programs

End users:


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Procedures

Instruction and rule that govern thedesign and use of the database system

Data


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Database System Types

Single-user vs. Multiuser Database(user number)

Desktop database

Workgroup database

Enterprise database

Centralized vs. Distributed (location)

Use

Production or transactional

Decision support or data warehouse

(obtain information)


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DBMS Functions

Objective: Guarantee the integrity andconsistency of data. It has several functions: Data dictionary management: (the definition of

the data elements and their relationships arestored in a data dictionary). It remove data and

structure dependencies. Data storage management: structures required

for data storage Data transformation and presentation: relieving

us from the distinct between logical data format

and physical data format Security management Multiuser access control (concurrency)


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DBMS Functions

Backup and recovery management Data integrity management

Database access language and

application programming interfaces Query language (DDL and DML)

Database communication interfaces


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Database Models

Definition: collection of logical constructs

used to represent data structure andrelationships within the database Conceptual models: logical nature of data

representation; if emphasizes on what entity is

presented; it is used for database design asblueprint

Implementation models: emphasis on how thedata are represented in the database


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Database Models

Conceptual models include

Entity-relationship database model (ERDBD) Object-oriented model (OODBM)

Implementation models include

Hierachical database model (HDBM)

Network database model (NDBM)

Relational database model (RDBM)

Object-oriented database model (ODBM)


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Relationships in Conceptual Models

One-to-one (1:1)

One-to-many (1:M) Many-to-many (M:N)

Implementation Database Models

Hierarchical Network

Relational

Object-Oriented

Database Models (cont.)


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Hierarchical Database Model

(HDBM)

Logically represented by an upside down tree

Each parent can have many children (segmentlinkage)

Each child has only one parent


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Logically represented by an upside down tree 1:M relationship


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Hierarchical path (beginning from left) Left-list hierarchical path, or preorder traversal,

or hierarchical sequence

Re-list sequence, if the segment is frequentlyaccessed

Bank systems commonly use HD model

Final assembly->Component A->Assembly A-> -> PartA ->Part B -> Component B -> Component CAssembly B -> Part C ->Part D


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Bank systems commonly use the HDBM customer account can be subject to many transactions (1:M

relationship)

Relationship is fixed (debiting and crediting)

Frequently access large amount of transactions


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Advantages

Conceptual simplicity: relationship between layers islogically simple; design process is simple

Database security: enforced uniformly through thesystem

Data integrity

Data independence

Efficiency in 1:M relationships and when uses requirelarge numbers of transactions

Dominant in 1970s , when we used mainframe systemwith large databases


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Disadvantages

Complex implementation: physical data storagecharacteristics; database design is complicated

Difficult to manage and lack of standards Lacks structural independence

Applications programming and use complexity

(pointer based) Implementation limitations, i.e. especially it only

handle 1:M type of model


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Network Database Model

(NDBM)

Each record can have multiple parents Called by Database Task Group (DBTG) to define

standards

Three crucial database components Network schema: conceptual organization of the entire database

Subschema: portion of database as information for applicationprograms

Database management language: defining data characteristics

and data structure Schema Data definition language (DDL): define schema

components

Subschema Data definition language

Data manipulating language: manipulate data content


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Each record can have multiple parents Introduce set to describe relationship

Each set has owner record and member

record, parallel to parent and child in HDM Member may have several owners

One-ownership


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Member may have several owners


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Advantages Conceptual simplicity, just lime HDM

Handles more relationship types (but all1:M relationship)

Data access flexibility

Promotes database integrity

Data independence

Conformance to standards


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Disadvantages

System complexity

Lack of structural independence


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Relational Database Model

(RDBM)

Lets user or database designer to operate humanlogical environment

Perceived by user as a collection of tables for datastorage, while let RDBMS handles the physicaldetails.

Tables are a series of row/column intersections

Tables related by sharingcommon entitycharacteristics

It allows 1:1, 1:M, M:N relationships


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Relational Database Model Advantages

Structural independence: data access path is is

irrelevant to database design; change structure willnot affect the database

Improved conceptual simplicity

Easier database design, implementation,management, and use

Ad hoc query capability with SQL (4GL is added)

Powerful database management system


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Disadvantages

Substantial hardware and system softwareoverhead

Poor design and implementation is made easy

May promote islands of information problems


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Entity Relationship Database

Model (ERDBM)

Complements the relational data model concepts

ERDBM introduces a relational graphic

representation ERDBM is based on several components

Entity, tabled entity (in RDM)

Entity and entity set, a collection of like entities Each entity has attributes to describe the entity,

which is similar to field in table

Relationship and connection


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Model (ERDBM)

Represented in an entity relationship diagram

(ERD): Chens ERD model and Crows Foot

ERD Based on entities, attributes, and

relationships


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Model

entity

relationship

connection

M


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M:M


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Model

Advantages

Exceptional conceptual simplicity

Visual representation

Effective communication tool

Integrated with the relational database model


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Model

Disadvantages

Limited constraint representation Limited relationship representation (internal relationship

can not be depicted; multiple relationships)

No data manipulation language (no complete)

Loss of information content What will be the next one?


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Object-Oriented Database Model

(OODBM)

Semantic Data model (SDM)->Object-oriented DataModel (OODM)

Object-oriented concept:

Objects or abstractions of real-world entities are stored Attributes describe properties

Collection of similar objects is a class, similar to entity setbut contains procedure methods

Methods represent real world actions of classes

Classes are organized in a class hierarchy

Inheritance is the ability of object to inherit attributes andmethods of classes above it


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(OODBM)

Contains implementation and procedure operationinformation for more complicated data such asgraphics, video, and other metadata

Support transaction and information Reusability

Portable to powered computing system


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OO Database Model

Advantages

Adds semantic content

Visual presentation includes semantic content Database integrity

Both structural and data independence


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OO Database Model

Disadvantages

Lack of OODM

Complex navigational data access

Steep learning curve

High system overhead slows transactions


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DBMS, File Sys, Data Models[1]

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