IT2301 Database Management Systems dbmsict'cmb'ac'lk

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PREPARING FOR THE BIT
IT2301Database Management Systemsdbms_at_ict.cmb.ac
.lk
Preparing for BIT 31/05/2001
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Todays Agenda

• Two Modules for Semester 2
• Database Management Systems
• Fundamentals of Software Engineering

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Introduction to DBMSObjectives cont.

• Explain how four components hardware, software,
  data and people work together to form todays
  database systems.

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Key Terms cont.

• Database System
• A database, a database management system and
  appropriate hardware and personnel.

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Database System Hardware

• Set of physical devices on which a database
  resides. It consists of one or more computers,
  disk drives, CRT terminals, printers, tape
  drives, connecting cables and other auxiliary and
  connecting hardware.

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Database System Hardware cont.
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Key Terms cont.

• Database Management System
• Systems software that facilitates the management
  of a database.
• E.g. Oracle, Access, SQL Server

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Database System Software

• A database software includes two types of
  software
• General-purpose database management software,
  usually called the database management system
  (DBMS)
• Application software that uses DBMS facilities to
  manipulate the database to achieve a specific
  business function, such as providing reports or
  documents, which can be used by users.

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Database System Software cont.

• Application software is generally written
  standard programming language such as C, or it
  may be written in a language (commonly called a
  fourth-generation language) supplied with the
  DBMS.
• These programs utilise the command language of
  the DBMS and make use of the information
  contained in the data dictionary.

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Data Dictionary/Directory (Repository)

• A subsystem that keeps track of the
• definitions of all data items (metadata) in the
  database.
• relationships that exists between various data
  structures.
• indexes that are used to access data quickly.
• screen and report format definitions that may be
  used by various application programs.

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Metadata

• Data that describe the properties or
  characteristics of other data.
• Some of these properties include data
  definitions, data structures and rules or
  constraints. Item name, the data type, length,
  minimum and maximum allowable values (where
  appropriate) and a brief description of each data
  item.
• Metadata allow database designers and users to
  understand what data exist, what the data mean.
• Data without clear meaning can be confusing,
  misinterpreted or erroneous.

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Metadata
E.g. Data Item Value Name Type Length Min
Max Description Name Character 30 Employee
Name ID Number 9 Employee No. Dept Character 10
Dept. No. Age Integer 2 18 60 Employee
Age Name Character 15 Dept. Name Manager Number
9 Mgr. Emp. No. Employee No. (ID)
unique Manager is an employee of the organisation
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Program-Data/Data Independence

• The separation of data descriptions (metadata)
  from the application programs that use the data.
• In the database approach data descriptions are
  stored in a central location called the data
  dictionary. This property allows an
  organisations data to change and evolve (within
  limits) without changing the application program
  that process the data.

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Components of a DBMS
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Database System People

• Two different types of people (users and
  practitioners) are concerned with the database.
• Users
• who need information from the database to carry
  out their primary business responsibility
• e.g. Executives, managers, staff, clerical
  personnel

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Database System People cont.

• Practitioners
• people responsible for the database system and
  its associated application software.
• e.g. Database administrators, analysts,
  programmers, database and system designers,
  information systems managers.

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Components of a Database System

• Four components People, H/W, S/W, Data
• Practitioners (analysts and database designers)
  in consultation with users identify data needs
  and design database structures to accommodate
  these needs.
• The database structures are specified to the DBMS
  through the data dictionary.

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Components of a DBS cont.

• Users enter data into the system by following
  specified procedures.
• The entered data are maintained on hardware media
  such as disks and tapes.
• Application programmes that access the database
  are written by practitioners and users to be run
  on computers.

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Components of a DBS cont.