Lec-1 Introduction to Databases

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    DATABASE MANAGEMENT SYSTEMS (BIS3103)

    Lecturer: Alice Nandawula Mugisha

    Email: amugisha@cit.mak.ac.ug

    Room: Room 202 (Staff Working Space), Block A

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    mailto:amugisha@cit.mak.ac.ugmailto:amugisha@cit.mak.ac.ug
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    CHAPTER 1Introduction to Databases2

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    OBJECTIVES

    Characteristics of file-based systems.

    Problems with file-based approach.

    Meaning of the term database.

    Meaning of the term Database Management System

    (DBMS).

    Typical functions of a DBMS.

    Advantages and disadvantages of DBMSs.

    Some common uses of database systems

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    FILE-BASED SYSTEMS

    A file is a collection of records which

    contain logically related data.Collection of application programs that

    perform services for the end users (e.g.

    reports).

    Each program defines and manages its own

    data.

    Better alternative to paper based filing

    systems.4

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    FILE-BASED APPROACH

    A system of files and collection of applicationprograms manipulating them is a file-basedsystem

    The UniversitysFile-Based System

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    LIMITATIONS OF FILE-BASED APPROACH

    Separation and isolation of data

    Each program maintains its own set of data.

    Users of one program may be unaware of

    potentially useful data held by other programs.

    Duplication of data

    Same data is held by different programs.

    Wasted space and potentially different values and/ordifferent formats for the same item.

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    LIMITATIONS OF FILE-BASED

    APPROACH

    Data dependence

    Unhealthy dependency between data and programs.Filestructure is defined in the program code.

    Incompatible file formats Programs are written in different languages, and so

    cannot easily access each others files.

    Fixed Queries/Proliferation of application programs

    Programs are written to satisfy particular functions. Anynew requirement needs a new program.

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    DATABASE APPROACH

    Arose because:

    Definition of data was embedded inapplication programs, rather than beingstored separately and independently.

    No control over access and manipulationof data beyond that imposed byapplication programs.

    Therefore there was a need to

    separate data from programs but witha facility for them to interact.

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    DATABASE APPROACH

    Result

    the database and Database ManagementSystem (DBMS).

    Databases were therefore developed tostore, organize and secure data whileapplications can be able to access thedatabase, process the data and generatethe required information. 9

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    DATABASE

    Shared collection of logically related data (and adescription of this data), designed to meet theinformation needs of an organization.

    System catalog (metadata) provides description ofdata to enable programdata independence.

    Logically related data comprises entities,attributes, and relationships of an organization'sinformation.

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    DATABASE APPROACH

    Data definition language (DDL).

    Permits specification of data types, structures and anydata constraints that should be part of the database.

    All specifications are stored in the database.

    Data manipulation language (DML). Enables those with access to the database to insert,

    update, delete and retrieve data from it.

    Standard Query Language (SQL) is an example of a

    DML

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    DATABASE ENVIRONMENT PLAYERS

    Data Administrator: Responsible over the data policies in

    the organization. Does not need to be a technical person. Database Administrator: Puts into practice the data

    policies of the organization, like back ups, recovery,

    integrity, security, availability, performance and testing

    support.

    Applications Program Developer: Responsible over

    development of the application programs that make use of

    the data in the database.

    User: Makes use of the information from the applications

    that talk to the database. The user may be novice or

    sophisticated

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    DATABASE MANAGEMENT SYSTEM

    (DBMS)

    DBMS: A software system that enables

    users to define, create, and maintain the

    database and which provides controlled

    access to this database.

    Database Application: A computer programthat interacts with the database by issuing an

    appropriate request (typically an SQLstatement) to the DBMS.

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    FUNCTIONS OF A DBMS

    Authorization Services.

    Support for Data Communication.

    Integrity Services.

    Services to Promote Data Independence.

    Utility Services.

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    ADVANTAGES OF DBMS

    Control of data redundancy

    Data consistency

    More information from the same amount of data.

    Sharing of data Improved data integrity

    Improved security

    Enforcement of standards

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    ADVANTAGES OF DBMS

    Balanced conflicting requirements

    Improved data accessibility and responsiveness

    Increased productivity

    Improved maintenance through data independence Increased concurrency

    Improved backup and recovery services

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    DISADVANTAGES OF DBMS

    Complexity

    Size

    Cost of DBMS

    Additional hardware costs Cost of conversion

    Performance

    Higher impact of a failure

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    DATA BASE MODELS

    A database model is an organizational principleused in organizing data by a databasemanagement system.

    Different database management systems of thesame model have the same principle of dataorganization. e.g. MS Access, Oracle and MicrosoftSQL server use tables (relations) to organize thedata.

    They are 'Relational' database managementsystems.

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    TYPES OF DATABASE MODELS The Network Model: Represents data as nodes and

    relationships are implied by linking up the nodes by

    edges. The Hierarchical Model: Represents data and nodes

    in a hierarchical manner.

    The Deductive Model: Represents minimal data as'Axioms'. Extra data and relationships are deduced.

    The Relational Model: Uses relations/table toorganize data. A row/tuple represents an instance ofdata and relationships are represented by foreignkeys.

    The Object Oriented Model: Uses the objectoriented paradigm of encapsulation, inheritance andpolymorphism. A class represents data and an objectrepresents the instance.

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