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Database system

Concepts of database management-3rd edition Philip j.pratt.2000

A database is a construction that contains information about many different classs of information and about the relationships between the classs. Premiere merchandises are a distributor of contraptions, housewares. The company has used dispersed sheet package to keep client, order, stock list and sales.The premiere productsdatabase, for illustration, will incorporate information about gross revenues, reps, clients, orders and parts. It will besides supply facts that relate gross revenues reps to the clients they represent and clients to the orders they presently have placed.

With the usage of database, employees can come in the figure of a peculiar order and happen out which client placed the orders, every bit good as which parts were ordered.

An entity is a individual topographic point object event of thought for which you want to hive away and treat informations. An property is a characteristic or belongings of an entity. For the entity for illustration the list of properties might include such things as auto coloring material and size.

Rep.

Rep. no.

Last name

First name

Street

City

State

Nothing

Commission

Rate

theoretical account

Properties

An property is besides called a field or column in many database systems.

A relationship is an association between entities. There is an association between reps and clients, for illustration at premiere merchandises. A rep is associated with all of his or her clients and a client is associated with its rep.

One-to-many relationship

Each rep is associated with many clients, but each client is associated with merely one rep. & A ; Acirc ; in this type of relationship, the word many is used otherwise than in mundane English ; it might non ever indicate a big a big figure. In this context, for illustration, the many means that a rep can be associated with any figure of clients. This is, a given rep can be associated with nothing, one, Or more clients.

A database is a construction that can hive away information about multiple types of entities, the properties of those entities, and the relationship among the entities. A database, nevertheless, is much more than a file. Unlike a typical information file, a database can hive away information about multiple entities. There is besides another difference. A database holds information about the relationship among the assorted entities. Not merely will premiere merchandises database hold information about reps and clients, it besides will keep information associating reps to the clients they service, clients to orders, parts to orders and so on.

Redundancy

It is the duplicate of informations or the storing of the same information in more than one topographic point. In the orders spreadsheet, redundancy occurs in the client name column because the name of a client is stored in more than one topographic point.

What jobs does redundancy do?

It wastes infinite because you are hive awaying the same information in multiple topographic points. The excess infinite consequences in larger spreadsheet that require more infinite in memory and on disc and that take longer to salvage and open.

When you need to alter informations, redundancy besides makes your alterations more hard and clip consuming.

Finally redundancy can take to struggles. For eg. If you enter person ‘s name and reference in different columns than it will take clip to come in and there is opportunity of doing errors.

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