working with the database management system

8/7/2019 Working with the Database Management System

http://slidepdf.com/reader/full/working-with-the-database-management-system 1/15

Working with the Database

Management SystemMS Access

Generally, a database is a collection of related

information that is organized in a table with rowsand columns. A database can include text,

pictures, sound and animations. It can be created

manually, as with the traditional filling system, or

electronically, as when organizing and maintainingdata in a computer system.

In a more specific sense, a database is a collection of interrelated files that is created

and managed by a database software called a Database Management System(DBMS).



Example of Database



Database Management

SystemA database management system (DBMS) consists

of software that operates databases, providing storage,access, security, backup and other facilities. Databasemanagement systems can be categorized according to

the database model that they support, suchas relational orXML, the type(s) of computer they support,such as a server cluster or a mobile phone, the query

language(s) that access the database, suchas SQL or XQuery, performance trade-offs, such as

maximum scale or maximum speed or others. Some DBMS

cover more than one entry in these categories, e.g.,supporting multiple query languages. Examples of some

commonly used DBMS are MySQL, PostgreSQL, MicrosoftAccess, SQL Server, FileMaker,Oracle,Sybase, dBASE,

Clipper,FoxPro etc. Almost every database software comeswith an Open Database Connectivity (ODBC) driver thatallows the database to integrate with other databases.



Database - Advantages &Disadvantages

Advantages y Reduced data redundancy y Reduced updating errors and increased

consistency y Greater data integrity and independence from

applications programs y Improved data access to users through use of host

and query languages y Improved data security y Reduced data entry, storage, and retrieval costs y

Facilitated development of new applicationsprogram

Disadvantages y Database systems are complex, difficult, and time-

consuming to design y

Substantial hardware and software start-up costs y Damage to database affects virtually allapplications programs

y Extensive conversion costs in moving form a file-based system to a database system

y Initial training required for all programmers



Developing a DatabasePlan

T he first step in creating a database is creating aplan that serves both as a guide to be used whenimplementing the database and as a functional

specification for the database after it has beenimplemented. T he complexity and detail of adatabase design is dictated by the complexity andsize of the database application and also the userpopulation.

Th e nature and complexity of adatabase application, and also t h eprocess of planning it, can varysignificantly. A database can be

relatively simple and designed for useby a single person, or it can be largeand complex and designed, forexample, to h andle all t h e bankingtransactions for t h ousands of



clients. In t h e first case, t h e databasedesign may be slig h tly more t h an afew notes on some scratc h paper. In

t h e latter case, t h e design may be aformal document h undreds of pageslong t h at contains every possibledetail about t h e database.

In planning the database, regardless of its sizeand complexity, use the following basic steps:

y Gather information.y Identify the objects.y Model the objects.y Identify the types of information for each

object.y Identify the relationships between objects.



Gathering Information

Before creating a database, you musth ave a good understanding of t h e job t h edatabase is expected to perform. If t h edatabase is to replace a paper-based ormanually performed information system,

t h e existing system will give you most oft h e information t h at you need. Yous h ould interview everyone involved int h e system to determine w h at t h ey doand w h at t h ey need from t h e database. It

is also important to identify w h at t h eywant t h e new system to do, and also toidentify t h e problems, limitations, andbottlenecks of any existing system.Collect copies of customer statements,

inventory lists, management reports, andany ot h er documents t h at are part oft h e existing system, because t h ese willbe useful to you in designing t h edatabase and t h e interfaces.



Identifying the Objects

During t h e process of gat h ering information,you must identify t h e key objects or entitiest h at will be managed by t h e database. Th e objectcan be a tangible t h ing, suc h as a person or aproduct, or it can be a more intangible item, suc h as a business transaction, a department in a

company, or a payroll period. Th ere aregenerally a few primary objects, and after t h eseare identified, t h e related items become visible.Eac h distinct item in your database s h ould h ave acorresponding table.

T he primary object in the AdventureWorks2008R2sample database included with SQL Server is a bicycle.T he objects related to bicycle within this company'sbusiness are the employees who manufacture thebicycle, the vendors that sell components used tomanufacture the bicycle, the customers who buy them,

and the sales transactions performed with thecustomers. Each of these objects is a table in thedatabase.



Mo deling the Objects

As the objects in the system are identified, youshould record them in a way that representsthe system visually. You can use your databasemodel as a reference during implementation ofthe database.

For this purpose, database developers use toolsthat range in technical complexity from pencils

and scratch paper to word processing andspreadsheet programs, and even to software

programs created specifically for the job ofdata modeling for database designs. Whatevertool you decide to use, it is important that you

keep it up to date.



Identifying t h e T ypes ofInformation for Eac h

Object

After the primary objects in the database have beenidentified as candidates for tables, the next step is to

identify the types of information that must be stored for each object. These are the columns in the table of theobject. The columns in a database table contain a fewcommon types of information:

y R aw data columns

These columns store tangible pieces of information,such as names, determined by a source external tothe database.

y C ategorical columns

These columns classify or group the data and store alimited selection of data such as true/false,married/single, and VP/Director/Group Manager.

y Identifier columns



These columns provide a mechanism to identifyeach item stored in the table. These columnsfrequently have an ID or number in their name, for example, employee_id, invoice_number, andpublisher_id. The identifier column is the primarycomponent used by both users and internal databaseprocessing for gaining access to a row of data in thetable. Sometimes the object has a tangible form of ID used in the table, for example, a social security

number, but in most situations you can define thetable so that a reliable, artificial ID can be createdfor the row.

y R elational or referential columns

These columns establish a link between informationin one table and related information in another table.For example, a table that tracks sales transactionswill generally have a link to the customers table sothat the complete customer information can beassociated with the sales transaction.



Identifying t h e Relations h ipBetween Objects

O ne of the strengths of a relational database is the ability torelate or associate information about various items in thedatabase. Isolated types of information can be storedseparately, but the database engine can combine data when it is required. Identifying the relationship between objects in thedesign process requires looking at the tables, determining how they are logically related, and adding relational columns that establish a link from one table to another.

For example, the designer of the AdventureWorks2008R2database has created tables for products and product modelsin the database. The Production.Product table contains

information for each product that includes an identifiercolumn named ProductID; data columns for the product name, the price of the product, and the product color, size,and weight. The table contains categorical columns, such asClass, or Style, that lets the products be grouped by thesetypes. Each product also has a product model, but that

information is stored in another table. Therefore, theProduction.Product table has a ProductModelID column tostore just the ID of the product model. When a row of data isadded for a product, the value for ProductModelID must exist in the Production.ProductModel table.



Designing Databases

Designing a database requires anunderstanding of the business functions youwant to model. It also requires anunderstanding of the database concepts andfeatures that you want to use to representthose business functions. Make sure that youaccurately design the database to model the

business, because it can be time-consuming tosignificantly change the design of a databaseafter you implement it. A well-designeddatabase also performs better.



In This Section

Topic DescriptionDeveloping aDatabase Plan

Describes the purpose of thedatabase and how it affectsthe design. Providesguidelines for creating a

database plan to fit your purpose.

OnlineTransactionProcessing vs.Decision Support

Describes the characteristicsof Online TransactionProcess (OLTP) andDecision Supportapplications and their effecton the design considerationsfor a database.

Normalization Describes databasenormalization rules that helpprevent mistakes in thedatabase design.

Data Integrity Describes how to help



protect the data integrity of the database.

Using Extended

Properties onDatabase Objects

Describes how to use

extended properties to adddescriptive or instructionaltext, input masks, andformatting rules asproperties of objects in a

database or of the databaseitself.

Estimating theSize of a Database

Provides procedures for estimating how large thedatabase will be when it is

filled with data.Designing Filesand Filegroups

Describes how to use filesand filegroups to managedatabase growth, enhancebackup and restorestrategies, and improvedatabase performance.

working with the database management system

Documents