DB Lecture 1

8/3/2019 DB Lecture 1

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Course Diploma in Business Information and Communication Technology

(DBICT I)

Ante: CIT 056

Subject: Theories and application of database management

Lecture : Data and Information

Facilitator Mr.Shadrack Madila.(BE.CSE)

Moshi

University

College of

Co-

operative

and

Business

Studies.

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Theories and Applications of database Management


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DATA

Data are collection of facts, or data refer to any type of information such as numbers,alphabets (A,B,C etc) or symbols such as comma (,), period (: ), it also refer to a name,

address ,words sentence as well as paragraph.

DATABASE

Is a collection of related data, typical describing the activities of one or more related

organizations. For example a university database might contain information about the

following

Entity- such as students, faculty, courses and classrooms.

Relationships-between entities such as students enrollment in courses, facultyteaching courses and the use of rooms for courses.

DATABASE MANAGEMENT SYSTEM (DBMS)

Is software designed to assist in maintaining and utilizing large collections of data, and

the need for such systems, as well as well their use.

DATA INTEGRITY

Refers to the correctness and consistency of stored data. It can be considered another

form of database protection. While it is related to security, it has broader implications;

Security involves protecting the data from unauthorized operations while integrity is

concerned with the quality of the data itself. Integrity is usually expressed in terms ofconstraints which are consistency rules that the database is not permitted to violate.

Types of integrity constraints

Data integrity is normally enforced in a database systemby a series of integrityconstraints or rules. Three types of integrity constraints are an inherent part of the

relational data model: entity integrity, referential integrity and domain integrity.

Entity integrityconcerns the concept of a primary key. Entity integrity is an integrity rulewhich states that every table must have a primary key and that the column or columns

chosen to be the primary key should be unique and not null.

Referential integrityconcerns the concept of a foreign key. The referential integrity rulestates that any foreign key value can only be in one of two states. The usual state of

affairs is that the foreign key value refers to a primary key value of some table in the

database. Occasionally, and this will depend on the rules of the business, a foreign keyvalue can be null. In this case we are explicitly saying that either there is no relationship

between the objects represented in the database or that this relationship is unknown.

Domain integrityspecifies that all columns in relational database must be declared upon adefined domain. The primary unit of data in the relational data model is the data item.

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Such data items are said to be non-decomposable or atomic. A domain is a set of values

of the same type. Domains are therefore pools of values from which actual values

appearing in the columns of a table are drawn.

CHARACTERISTICS OF GOOD INFORMATION

Good information is the kind that is useful (benefited). If someone inputs useless data

into a computer he/she will get useless information out of it.

Characteristics or properties of good information are:

1)Relevance- a report should give information relevant to the purpose meant for.

Irrelevant information is not useful or lead to wrong decisions, information should relate

to once information need.

2) Completeness- all needed information should be provided. In adequate informationmay not be very useful in a decision.

3)Accuracy- Information should be correct so as to make an informed decision. Correct

information is error free.

4) Understandable- Information will be useless if it cannot be understood, eg it must be

in a known language and readable.

5)Reliable- One who receives information eg. Managers must have confidence in it. In

addition, reliable information should be timely and up to date.

6)Passed to the right person- Correct information passed to the wrong decision makerwill not be relevant information to the owner. Information flows from bottom up

(subordinate to superior) or top down or below, people of equivalent rank.

7.Concise- most people are interested to read and comprehend a limited amount/volume

of information either they lack the time or find it is hard to read enormous volumes of

data. Reporting to the management for example must be in summary form. Just give therequired information.

8. Timing- quality information is required before the relevant decision is made. Otherwise

it will be of little or no value. Where information is to be provided on demand, requestsmust indicate when the information will be required so information must be timely i.e

provided when needed.

9. Value- benefits obtained from the information ought to be greater than the cost of

attaining it. Thus it may call for a cost cost/benefit analysis e.g information needs for

decisions to increase sales or reduce costs.

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THE HIERACHY OF DATA

Data Item

A data item is the smallest unit of information stored in computer file. It is a single

element used to represent a fact such as an student's name, item price, etc. In a student

database, the student number 170 is a data item. MIMI the name is a data item.

Field

Data items are physically arranged as fields in a computer file. Their length may be fixedor variable. Since all students have 10 digit student numbers, a 10-digit field is required

to store the particular data. Hence, it is a fixed field. In contrast, since student's names

vary considerably from one another, a variable amount of space must be available to store

this element. This can be called as variable field.

Record

A record is a collection of related data items or fields. Each record normally corresponds

to a specific unit of information. Students name, registration number and programregistered. This is the data used to produce the students register report. The first record

contains all the data concerning the first student. The second record contains all the dataconcerning the second. Each subsequent record contains all the data for a given student. It

can be seen how each related item is grouped together to form a record.

File

The collection of records is called a file. A file contains all the related records for an

application. Therefore, the student database for example contains all records required to

produce the students register report. Files are stored on some medium, such as floppydisk, magnetic tape or magnetic disk.

Table

All data held in a database is stored within a table. Usually many smalltables are created

rather than one large table. This helps the efficiency of thedatabase when searching for

information. Data can be entered, edited or deleted,directly in table, so no further objectsneed to be used to manipulate the data. When a table is opened, all the data held in the

table can be viewed on one large screen using scroll bars.

Database

Is a system for storing structured information, which is organized and storedin a way that

allows its quick and efficient retrieval.

OR

Is simply an organized collection of information, such as a telephone directory, address

book, etc.OR

The collection of related files is called a database. A database contains all the related files

for a particular application.

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MANUAL DATA PROCESSING (FILE DATA PROCESSING)

Before the advent of database systems, computer readable data was usually kept in files

stored on magnetic tape or disk. In a typical file processing system, each department hasits own set of applications and its own files, designed specifically for those applications.

The department itself, working with the data processing staff, sets policies or standards

for the format and maintenance of its files.

ADVANTAGES OF DATABASE

Compared with the traditional file processing approach, the database system approach hasseveral advantages.

1. Sharing of data

Unlike files which are owned by the departments whose applications they serve, thedatabase belong to the entire organization. The DBA manages the data, but it does not

belong to any individual or department. Many user can be authorized to access the

same piece of information.

2. Control of Redundancy

In database systems data are integrated so that several copies of of the same data arestored. Some limited redundancy are permitted to keep logical connections among

data items or to improve performance, but the system is usually aware of which items

are stored twice.

3. Data consistency

One effect of eliminating or controlling redundancy is that the data is consistent. If a

data item appears only once, any update to its value needs to performed only once, andall users have immediate access to the new value. If the system has some controlled

redundancy when it receive an update to an item that appears more than once it can

often do cascading update, automatically updating every occurrence of that item,keeping the database consistency.

4. Improve data standards

The DBA who is responsible for designing and maintaining the database to serve the

needs of all users, must define and enforce organization wide standards for

representation of data in the database this includes such concerns as the format of all

data items, conventions on data names, documentation standards, frequency of updateupdate procedures, and permitted usage of the database.

5. Better data security

Data security is the protection of database from unauthorized access. All authorized

Access to the database is through the DBMS, which can require that users go through

Security procedures or use additional passwords to gain access to the data.

6. Improved data integrity

some database management systems allow the DBA to define integrity constraints, or

consistency rules that the data base must obey. These constraints may apply to items

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within a record (intra record constraints), or to the relationship between records (inter

record constraints) or may be general constraints. For example, in a course records

there may be a rule that the number of students enrolled in a course may never exceedthe maximum enrollment.

7. Faster development of new applicationsA well designed database provides an accurate model of the operations of the

organization. When a new application is proposed, it is likely that the data required is

already stored in the database. Development time is reduced because no file creationphase is needed for the new application.

8. Better data accessibility

Most database management systems allow on-line access users. They provide querylanguages that permit users to ask one of a kind questions and obtain the required

information at interactive terminals, rather than by waiting for a programmer.

9. Economy of scaleWhen all of the organizations data requirements are satisfied by one database instead

of many separate files, the size of the combined operation provides severaladvantages. The portion of the budget that would ordinarily be allocated to various

departments for their data design, storage and maintenance costs can be pooled,

possibly resulting in a lower cost.

10. More control over concurrency

In a file system if, two users are permitted to access data simultaneously, it is

possible that they will interfere with each other. For example, if both attempt toperform updates, one update may be lost, because one may overwrite the value

recorded by the other. Most database management systems to control concurrency so

that transactions are not lost or performed incorrectly.

11. Better backup and recovery procedures

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DISADVANTAGE OF DATABASE SYSTEM

1. HIGH COST OF DBMS

Because a complete database management system is a very large and

sophisticated piece of software, it is expensive to purchase or lease.

2. HIGHER HARDWARE COSTS

Additional memory and processing power may be required to run the DBMS, resulting

in the need to upgrade hardware.

3. HIGHER PROGRAMING COSTS

Because a DBMS is a complex tool with many features, the organizations

programmers need a high knowledge of the system to use it to the best advantage .

4. HIGHER CONVERSION COST

When an organization converts to a database system, data has to be removed from

from files and loaded into the database. Because of different formats used in files, thismay be a difficult and time consuming process.

5. INCREASED VULNERABILITY

Whenever resources are centralized, there is an increased security risk. The integration

of files also make a failure more serious. Since all applications depend on the database

system, the failure of any component can bring operations to a standstill.

6. MORE DIFFICULT RECOVERY

The recovery process after a system failure is more complicated because the systemmust determine which transactions were completed and which were in progress at the

time of failure. The transactions involving several database changes that where in

progress at the time of failure may have update some value and not others.

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DB Lecture 1