42484900 Database Basics

7/28/2019 42484900 Database Basics

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Database Management Systems


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DBMS

A database management system (DBMS) is aset of computer-based application programsthatsupportthe processes ofstoring,

manipulating, retrieving and presenting thedata within thedatabase.

Acts as an interfacebetween applicationprograms & physical data files

Thedata within thedatabase are organizedinto tables, records, andfields.


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Table

A table is the primary unit of physical

storage for data in a database.1

Usually a database contains more than

one table.


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Table


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A Database with Multiple Tables

Publishers Books Customers

Authors Inventory Orders

[1]


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Table

Customers


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Field (Column)

a field

Customers


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Record (Row)

a record

Customers


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Primary Key

primarykey field

Customers

Primary key is a uniqueidentifierofrecordsin a table.

Primarykeyvaluesmaybe generatedmanuallyorautomatically.


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Primary Key

primarykey fields

Roles (Performances)

Aprimarykeycanconsistofmorethanone field.


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Foreign Key

foreignkey field

primarykey fieldparenttable

Directors

Movieschildtablerelationship


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Relationship Types

One-to-one

One-to-many

Many-to-many


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Data Types

Alphanumeric (Text, Memo)

Numeric (Number, Currency, etc.)

Date/Time Boolean (Yes/No)


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Database Environments

Mainframe

Client/Server

Internet-based


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Definitions Relational database: A collection of tables.

Table: A collection of columns (attributes) describing an entity. Individual

objects are stored as rows of data in the table.

Property (attribute): a characteristic or descriptor of a class or entity.

Every table has a primary key.

The smallest set of columns that uniquely identifies any row

P

rimary keys can span more than one column (concatenated keys) We often create a primary key to insure uniqueness (e.g., CustomerID,

Product#, . . .) called a surrogate key.

EmployeeID TaxpayerID LastName FirstName HomePhone Address12512 888-22-5552 Cartom Abdul (603) 323-9893 252 South Street

15293 222-55-3737 Venetiaan Roland (804) 888-6667 937 Paramaribo Lane

22343 293-87-4343 Johnson John (703) 222-9384 234 Main Street

29387 837-36-2933 Stenheim Susan (410) 330-9837 8934 W. Maple

Employee

Properties

Rows/Objects

Class: EmployeePrimarykey


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Characteristics of DBMS

Approach Self-contained nature Program-data independence

Dataabstraction

Support formultiple views

Centralised control of the dataresource reduces redundancy

avoids inconsistencies

datacan be shared

standards can be enforced

security restrictions can be applied integrity can be maintained

Sharing of data

Multiusertransaction processing


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Advantages of DB

ControllingR

edundancy Restricting Unauthorized Access

Providing persistent storage for program objects

Proving storage structures for efficient query

processing

Providing backup and recovery

Providing multi-user interfaces

Representing complex relationships among data Enforcing integrity constraints

Permitting inferencing and actions using rules

Additional implications of using the DB approach


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Classification of DBMS

Based on Data Model Relational, object, object-relational, hierarchical,

network

Based on number of users Single-user and Multi-user

Number of sites Centralized, Distributed, Homogeneous

Cost

Types of Access path General purpose or special purpose


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Actors on the DBMS Scene

Data administrator (DA)

Database administrator (DBA)

Database designers

Users

Casual end users

Application programmers


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Contents ofa Database

A Database contains:

User Data

Metadata

Indexes

Applications


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UserData

End-users work directly with the DBMS by entering, updating andviewing the data. Typically they would use a query language (SQL)

In a relational DB, data will be generally stored in tables with somerelationships between tables.

Each table has one or more columns (attributes). For example, below is a bank account table.

ustomer I cct umber cct T pe ate pene alance

heckin / / .

a in s / / .

a in s / / .

heckin / / .

a in s / / .

a in s / / .

heckin / / .


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Metadata

Data about data.

Data that describes how users data are stored in terms

of table name, column name, data type, length, primary

keys, etc. Metadata are typically stored in System tables and are

typically only directly accessible by the DBMS or by the

system administrator.

For example, the metadata for the bank account table,

could be:


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Indexes

Allow users to access a specific record without having to search

through the entire table

For example, indexes would be used to find all customers who

opened the account before 01/01/2000. In this case the bank account

table is indexed on date opened attribute (see below)

Indexes provide efficient data access on one hand, but are

expensive to maintain: Updating data requires an extra step:

Index(s) must also be updated.

ustomer I Acct umber Acct pe ate Opened alance

100 hecking 11/1 /1 00.00100 2 avings /22/1 00.00

1001 hecking 10/12/1 000.00

1001 0 avings 10/12/1 2000.00

1002 11 avings 1/ /1 10000.00

100 22 hecking 10/1/2000 000.00

100 2 avings 12/11/2000 000.00


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Forms/Report

Generators/Application Programs

Many DBMS have the capability to handle forms (for users to

enter/access/update data), reports, and other application

components.

Report is an organized representation, designed to be printed, of

the information in your tables or queries. You can create a reportfrom a single table or from a query of two or more tables

Query allows you to ask questions of your information. Database

management system, such as Microsoft Access would use your

questions to generate a subset of he data in your database.

Form is a convenient way to enter or find information in tables.

Applications are various programs written in various languagesto access and manipulate the data. Each application is

designed for a specific aspect of a given functional area, e.g.,

payroll application, accounting, etc.


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Data Modeling and Database

Design Database Schema: The structure of a database that: Represents data elements, data types, relationships among data

elements, and constraints on data

Is independent of any application program

Typically, changes infrequently Data Model:

A set of primitives for defining the structure of a database.

A set of operations for specifying retrieval, and updates on a database.


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Design - example

Design tables forthe following scenario:-

Stock management ofacompany

500 items

Three types (A/B/C)

Items receipt and issues on a daily basis

Generate reports

42484900 Database Basics

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