Introduction DBA

8/13/2019 Introduction DBA

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Database Administration--Introduction 1

The amount of information available to us areliterally exploding

Managing large amounts to data correctly and fast tomake data an asset than a liability

Businesses as main reason for the development ofDBMS(transactions, processes, and over viewing)

A database is a collection of data, typically describing the

activities of one or more related organizations. For example, a

university database might contain information about the

following:

Entities such as students, faculty, courses, andclassrooms.

Relationshipsbetween entities, such as students'enrollment in courses, faculty teaching courses, and

the use of rooms for courses.

Database Applications:

Banking: all transactions

Airlines: reservations, schedules

Universities: registration, grades

Sales:customers, products, purchases

Manufacturing: production, inventory, orders, supplychain

Human resources: employee records, salaries, taxdeductions

A database management system, or DBMS, is software

designed to assist in maintaining and utilizing large collections

of data, and the need for such systems, as well as their use, is

growing rapidly.

File Systems, on the other hand, is the management of files

within an organization without the help of machines, thus only

incorporating manual process of storage and retrieval of data.

File Systems vs Database Systems

Disadvantages of File Systems

Data redundancy and inconsistency

Difficulty in accessing data

Data isolation

Integrity problems

Atomicity of updates

Concurrent access by multiple users

Security problems

Advantages of DBMS

Data independence Efficient data access

Data integrity and security

Data administration

Concurrent access and crash recovery

Reduced application development time

People who deal with databases:

Database implementers-who builds the DBMS software

End users-who uses the DBMS, storing and retrieval of data

Database application programmers

Develop packagesthat facilitate data access for endusers

Uses data languages and DBMS tools

Database Administrator

Design of the conceptual and physical schemaresponsible for interacting with the users of the

system to understand what data is to be stored in the

DBMS and how it is likely to be used. Must design

the conceptual schema and the physical schema

Conceptual Schema- The layout of reports,

screens, forms, web pages, and other data entry

and presentation vehicles are finalized during

this phase

Physical Schema- actual hardware and systems

software that will be used to implement the

application(s) and database(s)

Security and authorizationensures thatunauthorized data access is not permitted. Not

everyone should able to access data. Usually, end

users have the lowest access level

Data availability and recovery from failuresensure that when the system fails, user can continue

to access much of the corrupted data as possible.

Restores data into a consistent state. Backs up data

periodically and maintain logs of activity.

Database tuningusers needs evolves every time.Responsible for modifying the database.

Levels of Abstraction

Physical leveldescribes how a record (e.g.,customer) is stored.

Logical level:describes data stored in database, andthe relationships among the data.

typecustomer = recordname: string;

street: string;

city: integer;

end;

View level:application programs hide details of datatypes. Views can also hide information (e.g., salary)

for security purposes.


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Elements of a Database

Database SchemaSchema-structure of the database

Logical Schema- describes the stored data in terms of thedata model of the DBMS

Example:

Students(sid: string, name: string, login: string,

age: integer,gpa: real)

Faculty(_d: string,fname: string,sal: real)

Courses(cid: string, cname: string, credits: integer)

Rooms(rno: integer, address: string, capacity:

integer)

Enrolled(sid: string, cid: string,grade: string)

Teaches(_d: string, cid: string)

Meets In(cid: string, rno: integer, time: string)

Physical Schema- summarizes how the relationsdescribed in the conceptual schema are actually stored on

secondary storage devices

External Schema-allow data access at the level ofindividual users

Tables-primary unit of physical storage for data in a database

Field-special category of information that exists in a table

Records-a row of data in a table

Data Types-type of data to be stored in a database record

-commonly used are letters, number, date and time

Primary Keys-unique value in the record, used to join tables

Foreign Keys-values that references a primary key in another

table


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Relationships

One-to-oneOne record in a table is related to onlyone record in another table.

One-to-manyOne record in a table can be relatedto many records in another table.

Many-to-manyOne record in a table can berelated to one or more records in anothertable, and one or more records in the second tablecan be related to one or more recordsin the first table.

Database Models Flat-file database model-straight approach Hierarchical database model-parent/child relation Network database model-shares child table Object-oriented (OO) database model-w/ c++ or java Object-relational (OR) database model

Relational database model-allows us to describe datainvolved in a real world enterprise in terms of objectsand relationships

-most stable-easy to convert, define, manipulate-higher integrity level

The ER(Entity Relationship) ModelIt provides useful concepts that allows us to move from an

informal description of what users want from their database to

a more detailed, and precise, description that can be

implemented in a DBMS.

Entity sets Customer and Loan


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Attribues

ER Diagrams

Rectanglesrepresent entity sets.

Diamondsrepresent relationship sets.

Lineslink attributes to entity sets and entity sets torelationship sets.

Ellipsesrepresent attributes

Double ellipsesrepresent multivaluedattributes.

Dashed ellipsesdenote derived attributes.

Underlineindicates primary key attributes

Cardinality Constraints-We express cardinality constraints

by drawing either a directed line (), signifying one, or an

undirected line (), signifying many, between the

relationship set and the entity set.

Can also be expressed as Chens notation

*=many

1=one

0=none

A number can also limit the maximum allowed entries

Can also be expressed as crows foot(Barker Notation)

many

one to many

zero to many

one to one

Example problem,consider a hospital:

Patientsare treatedin a single wardby

the doctorsassigned to them. Usually each patient

will be assigneda single doctor, but in rare cases theywill have two.

Heathcare assistantsalso attendto the patients, a

number of these are associatedwith each ward.

Initially the system will be concerned solely with

drug treatment. Each patient is required to takea

variety of drugsa certain number of times per day

and for varying lengths of time.

The system must recorddetails concerning patient

treatment and staff payment. Some staff

are paidpart time and doctors and care assistants

work varying amounts of overtime at varying rates(subject to grade).

The system will also need to trackwhat treatments

are required for which patients and when and it

should be capable of calculating the cost

of treatmentper week for each patient.

Introduction DBA

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