Database Management Systems and the Database Environment

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Database Management Systems and the Database
Environment

• MSIT 124 Database Systems
• Lecture 2

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What is a database?

• A shared collection of logically related data
  (and a description of this data), designed to
  meet the information needs of an organization.
• A self-describing collection of integrated
  records.
• The description of the data is known as a system
  catalog, data dictionary or meta-data.

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What is a Database Management System (DBMS)?

• A software system that enables users to define,
  create and maintain the database and provides
  controlled access to this database.
• Examples MySQL, PostgreSQL, MS Access, Oracle

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• Database

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What is a file-based system?

• A collection of application programs that perform
  services for the end-users such as the production
  of reports.
• Each program defines and manages its own data.
• This is referred to as the file-based approach
  (in contrast with the database- approach) to
  systems development.

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Limitations of the File-Based Approach

• Separation and isolation of data
• Duplication of data
• Data dependence
• Incompatibility of files
• Fixed queries/proliferation of application
  programs

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Advantages of Database Approach

• Minimal data redundancy
• Consistency of data
• Integration of data
• Sharing of data
• Enforcement of standards
• Ease of application development
• Uniform security, privacy and integrity controls

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Disadvantages of the Database Approach

• Size
• Complexity
• Cost
• Additional hardware requirements
• Higher impact of a failure
• Recovery more difficult
• Requires new, specialized personnel

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Example of a Database - Conceptual Data Model

• Mini-world for the example Part of a UNIVERSITY
  environment
• Some mini-world entities (Data elements)
• - STUDENTs
• - COURSEs
• - SECTIONs (of COURSEs)
• - (academic) DEPARTMENTs
• - INSTRUCTORs

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Example of a Database - Conceptual Data Model
(contd.)

• Some mini-world relationships
• - SECTIONs are of specific COURSEs
• - STUDENTs take SECTIONs
• - COURSEs have prerequisite COURSEs
• - INSTRUCTORs teach SECTIONs
• - COURSEs are offered by DEPARTMENTs
• - STUDENTs major in DEPARTMENTs

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Entities, Attributes and Relationships
attributes

• ID Number
• Name
• Address
• Salary

Employee
relationship
entities
works
attributes

• Dept Code
• Name
• Location

Department
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What are entities, attributes and relationships?

• An entity is really just like a noun, an object
  it maybe a person, place, thing or concept. It is
  represented as a record in a database.
• An attribute is a property of an entity. It is
  represented as a field in a database record.
• A relationship is an association between
  entities. It is represented using a common field
  in a set of records.

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Major Components of a DBMS
Programmers
Users
DBA
DBMS
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Major Components of a Database Manager
DatabaseManager
DataManager
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Schematic Diagram of A DBMS
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Functions of a DBMS

• Data storage, retrieval and update
• User-accessible catalog or data dictionary
• Transaction support (updating)
• Concurrency control services (multiple updating)
• Recovery services
• Authorization services
• Support for data communication and networking

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Main Characteristics of Database Technology

• Self-contained nature of a database system
• A DBMS catalog stores the description
  (structure, type, storage format of each
  entities) of the database. The description is
  called meta-data). This allows the DBMS software
  to work with different databases.
• Insulation between programs and data
• Called program-data independence. Allows changing
  data storage structures and operations without
  having to change the DBMS access programs.
• Data Abstraction
• A data model is used to hide storage details and
  present the users with a conceptual view of the
  database does not include how data is stored and
  how the operations are implemented.

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Main Characteristics of Database Technology
(contd)

• Support of multiple views of the data
• Each user may see a different view of the
  database, which describes only the data of
  interest to that user.
• Sharing of Data and Multiple users
• DBA Database Administrator
• Responsible for authorizing access to the
  database, coordinating, monitoring its use,
  acquiring hardware, software needed
• Database Designers
• Responsible for identifying the data to be
  stored, storage structure to represent
  and store data. This is done by a
  team of professionals in consultation
  with users, and
  applications needed.

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Benefits of Database Technology

• Controlling redundancy in data storage and in
  development and maintenance efforts.
• Sharing of data among multiple users.
• Restricting unauthorized access to data.
• Providing multiple interfaces to different
  classes of users.
• Representing complex relationships among data.
• Enforcing integrity constraints on the database.
• Providing backup and recovery services.
• Potential for enforcing standards.
• Flexibility to change data structures.
• Reduced application development time.Availability
  of up-to-date information.
• Economies of scale.

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When not to use a DBMS

• Main inhibitors (costs) of using a DBMS
• High initial investment and possible need for
  additional hardware.
• Overhead for providing generality, security,
  recovery, integrity, and concurrency control.
• When a DBMS may be unnecessary
• If the database and applications are simple, well
  defined,and not expected to change.
• If there are stringent real-time requirements
  that may not be met because of DBMS overhead.
• If access to data by multiple users is not
  required.
• When no DBMS may suffice
• If the database system is not able to handle the
  complexity of data because of
  modeling limitations
• If the database users need special operations not
  supported by the DBMS.

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