Introduction to Database Systems

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Introduction to Database Systems

• What is a Data
• What is a Database
• What is a Database System
• History of Databases
• Relational Model
• Relational Model Advantages

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What is Data ?

• Data is defined as isolated facts which are
  stored in the database.
• Whereas Information is defined as the meaning
  of the data or processed data which is important
  to the user.

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What is a Database ?

• A database is defined as a collection of
  persistent and interrelated data that is used by
  one or more application systems.

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What is a Database System ?

• A database system is composed of a database,
  hardware, software, and users or personnel.
• A Database Management System is used to manage
  all the pieces of a database system.

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DBMS components
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Hardware

• The hardware consists of the storage disks, I/O
  devices, processors, and main memory.
• Databases can be stored either on file systems or
  directly on disk partitions.

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Software

• The software deals with the database Management
  System (DBMS)
• The DBMS consists of a server, client, and tools.
• Tools consist of application development, design
  tools and utilities.

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Users

• There are different classes of users for database
  systems.
• 1) Application Programmers who write database
  applications
• 2) End users who interact with the database
  system for processing jobs.
• 3) Database Administrators (DBAs) who help to
  run and administer the database.

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Database History

• File Oriented Systems
• Hierarchical Model
• Network Model
• Relational Model

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File Oriented Systems

• Early computer systems were used primarily for
  accounting processes.
• These systems were known as data processing
  systems
• The files in these systems are sequentially
  accessed and normally were processed in batch
  mode.
• Most application programs evolved from this
  process.

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Random Access Processing

• File Oriented systems didnt allow for random
  access processing
• Random Access Processing the ability to directly
  access a given record without first sorting the
  file or reading records of a file in a sequence.

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Limitations of File Systems

• 1) It is usually impractical to obtain all the
  data if only one or more piece of data are
  required. This results in redundant data.

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Limitations of File Systems

• 2) The limited access to data makes it impossible
  to validate the same data in other files.
• 3) Ad Hoc queries to systems are not
  possible.

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Other Limitations of Traditional Systems

• 1) Data redundancy---Many data items are found to
  be common to several applications.
• 2) Poor data control-- problems with inconsistent
  terminology

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Other Limitations of Traditional Systems

• 3) Inadequate data manipulation capabilities---
  Cannot access related data in different files
• 4) Excessive programming efforts---Heavy
  dependence between programs and data.

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Hierarchical Model

• First database systems introduced in the 1960s
  were based on the hierarchical model
• This model assumes all data relationships can be
  structured as hierarchies.
• Uses a parent and child relationship where a
  child can only have one parent.

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Hierarchical Model
Movies
Classics
Comedy
M.A.S.H
Casablanca
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Hierarchical Model Limitations

• Hierarchical Model still used today on some IBM
  mainframes such as IBMs IMS system.
• Need to redesign entire database to change how
  data is interrelated.
• Can lead to confusion in relationships of data.
• Only allows one parent record type.

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Network Model

• Network Model came about from the Conference on
  Data Systems Language (CODASYL).
• Design is based on data sets
• Similar to the hierarchical model with sequential
  access properties.
• Uses logically related data items to define
  record types.

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Network Model
Harrison Ford
Carrie Fisher
Tom Hanks
Star Wars
When Harry Met Sally
The Burbs
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Network Model Limitations

• As data sets are added so is the complexity and
  confusion.
• Procedural model of one record processing at a
  time.
• Difficult to change data once it is stored
• Need detailed understanding of the data and how
  it is stored.

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E.F. Codd

• In 1970 E.F. Codd published a paper that strongly
  challenged the conventional wisdom of the
  database establishment.
• Codd argued that data should be related through
  natural, logical relationships that were inherent
  in the data rather than through physical pointers.

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E.F. Codd continued

• Codd proposed that a simple data model would
  consist of data represented in tables made up of
  rows and columns. These tables were given the
  name of relations.
• Codd also proposed two languages for manipulating
  data in tables relational algebra and relational
  calculus.
• The results were the release of several
  relational database management systems.

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Relational Model

• Data is represented by rows and columns in
  tables.
• Relations are based on keys which interconnect
  the data.
• Data are restricted by constraints which follow
  rules of integrity

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Relational Model

• Column

• Row

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Advantages of Relational Model

• Data can be shared
• Redundancy can be reduced
• Speed Compactness less drudgery
• integrity can be maintained
• Standards can be enforced

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Vendors

• Oracle
• Sybase
• Informix
• Microsoft SQL Server

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Database System Architecture

• In 1978 ANSI committee proposed a generalized
  framework for database systems.
• This framework provided a three-level-architectur
  e at which a database could be used.

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Database System Architecture

• Internal Level
• External Level
• Conceptual or Logical Level

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ANSI 3-Level Architecture
End Users
Logical Designers
Physical Designers
External Level
Internal Level
Logical Level
Mapping
Mapping
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Conceptual Level

• This level is the one at which logical database
  design is done.
• The design involves the analysis of users
  information needs and the identification and
  definition of the data items to meet those needs.
• The results of this design is the logical or
  conceptual schema.

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Conceptual Level

• This level is the one at which logical database
  design is done.
• The design involves the analysis of users
  information needs and the identification and
  definition of the data items to meet those needs.

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Conceptual level continued

• The results of this design is the logical or
  conceptual schema.
• The schema is defined as the single logical
  description of all the data elements and their
  relationships.

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External Level

• The external level is the level which users view
  the database.
• It consists of the individual portions and /or
  derivations of the logical schema that apply to a
  particular group of users.
• The external level consists of all views of the
  user sets.
• Each user group will have its own view of the
  data.

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External Level

• The external level is the level which users view
  the database.
• It consists of the individual portions and /or
  derivations of the logical schema that apply to a
  particular group of users.
• The external level consists of all views of the
  user sets.
• Each user group will have its own view of the
  data.

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Internal Level

• This level is known as the physical level.
• It is concerned with the physical way the data is
  stored.
• This level is described by the internal schema
• The internal schema defines the stored record
  types.

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Internal Level continued

• No user is concerned with this level.
• This level is also concerned with database
  performance.

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Mappings

• The mappings concern the conceptual/internal
  mappings and the external/conceptual mappings.
• The conceptual/internal defines how the records
  and fields are stored.
• The external/conceptual mappings defines how
  the user views the database compared with the
  designer view.

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Client/Server Architecture

• A client server architecture consist of two
  parts.
• The server or backend which has the database.

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Client/Server Architecture

• The client or front end which houses the user
  applications which interact with the database.
• These clients connect through the
  external-level to the server

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Client-Server Diagram
Applications
Clients
USERS
DBMS
Database
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Distributed Processing

• Distributed Processing has to do with the idea of
  allowing multiple client machines to connect to
  one or more servers through a communications
  network.

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Clients
Communications Network
Server
Database