dbms interfaces

7/29/2019 DBMS Interfaces

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DBMS Interfaces

User-friendly interfaces provided by a DBMS may include the following.

?Menu-Based interfaces for Web Clients or Browsing: These interfaces present user

with lists of options, called menus, that lead the user through the formulation arequest. Menus do away with the need to memorize the specific commands and

syntax of a query language. Pull-down menus are a very popular technique in Web

based user interfaces. They are also often used in browsing interfaces, which allows auser to look through the contents of a database.

?Forms-Based Interfaces: A forms-based interface displays a form to each user.

Forms are usually designed and programmed for naive users as interfaces to cannedtransactions. Some systems have utilities that define a form by letting the end user

interactively construct a sample form on the screen.

?Graphical User Interfaces: A graphical interface (GUI) typically displays a schemato the user in diagrammatic form. The user can then specify a query by manipulatingdiagram. In many cases, GUls utilize both menus and forms. Most GUls use a

pointing device, such as a mouse, to pick certain parts of the displayed schema

diagram.

?Interfaces for Parametric Users: Parametric users, such as bank tellers, often have a

small set of operations that they must perform repeatedly. Systems analysts and

programmers design and implement a special interface for each known class of naiveusers. Usually, a small set of abbreviated commands is included, with the goal of

minimizing the number of keystrokes required for each request. For example,

function keys in a terminal can be programmed to initiate the various commands.

?Interfaces for the DBA. Most database systems contain privileged commands thatcan be used only by the DBA's staff. These include commands for creating account,

setting system parameters, granting account authorization, changing a schema, and

reorganizing the storage structures of a database.


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Database normalization

Database normalization is the process of organizing the fields and tables of a relationaldatabaseto minimize redundancy and dependency. Normalization usually involves

dividing large tables into smaller (and less redundant) tables and defining relationshipsbetween them. The objective is to isolate data so that additions, deletions, and

modifications of a field can be made in just one table and then propagated through therest of the database via the defined relationships.

What is Normalization?

Normalization is the process of efficiently organizing data in a database. There are twogoals of the normalization process: eliminating redundant data (for example, storing the

same data in more than onetable) and ensuringdata dependenciesmake sense (only

storing related data in a table). Both of these are worthy goals as they reduce the amount

of space a database consumes and ensure that data is logically stored.

The Normal Forms

The database community has developed a series of guidelines for ensuring that databases

are normalized. These are referred to as normal forms and are numbered from one (the

lowest form of normalization, referred to asfirst normal formor 1NF) through five (fifthnormal form or 5NF). In practical applications, you'll often see 1NF, 2NF, and 3NF.

Before we begin our discussion of the normal forms, it's important to point out that theyare guidelines and guidelines only. Occasionally, it becomes necessary to stray from them

to meet practical business requirements.

First Normal Form (1NF)First normal form (1NF) sets the very basic rules for an organized database:

Eliminate duplicative columns from the same table.

Create separate tables for each group of related data and identify each row with aunique column or set of columns (theprimary key).

Second Normal Form (2NF)

Second normal form (2NF) further addresses the concept of removing duplicative data:

Meet all the requirements of the first normal form.

Remove subsets of data that apply to multiple rows of a table and place them in

separate tables.

Create relationships between these new tables and their predecessors through theuse offoreign keys.
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Third Normal Form (3NF)

Third normal form (3NF) goes one large step further:

Meet all the requirements of the second normal form.

Remove columns that are notdependent upon the primary key.

Boyce-Codd Normal Form (BCNF or 3.5NF)

The Boyce-Codd Normal Form, also referred to as the "third and half (3.5) normal form",

adds one more requirement:

Meet all the requirements of the third normal form.

Every determinant must be a candidate key.( A candidate key is a combination of

attributes that can be uniquely used to identify a database record).
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