database final

Providing Multiple User Interfaces

Both forms-style interfaces and menu-driven interfaces are commonly known as graphical user interfaces (GUIs)

query and transation

A query2 typically causes some data to be retrieved; a transaction may cause some data to be read and some data to be written into the database

Database manipulation involves querying and updating. Examples of queries are as follows:

Retrieve the transcript—a list of all courses and grades—of 'Smith' ■ List the names of students who took the section of the 'Database' course offered in fall 2008 and their grades in that section ■ List the prerequisites of the 'Database' course

database sharing

Sharing a database allows multiple users and programs to access the database simultaneously

database are either

manual or computeirzed

Examples of updates include the following

■ Change the class of 'Smith' to sophomore ■ Create a new section for the 'Database' course for this semester

The main characteristics of the database approach versus the file-processing approach are the following:

■ Self-describing nature of a database system ■ Insulation between programs and data, and data abstraction ■ Support of multiple views of the data ■ Sharing of data and multiuser transaction processing

protection of database

. Protection includes system protection against hardware or software malfunction (or crashes) and security protection against unauthorized or malicious access

Providing Backup and Recovery

A DBMS must provide facilities for recovering from hardware or software failures. The backup and recovery subsystem of the DBMS is responsible for recovery

. A database has the following implicit properties:.

A database is a logically coherent collection of data with some inherent meaning. A random assortment of data cannot correctly be referred to as a database.

method for generate nd maintain databases

A database may be generated and maintained manually or it may be computerized.

. A database has the following implicit properties:

A database represents some aspect of the real world, sometimes called the miniworld or the universe of discourse (UoD)

Support of Multiple Views of the Data

A database typically has many users, each of whom may require a different perspective or view of the database

Self-Describing Nature of a Database System

A fundamental characteristic of the database approach is that the database system contains not only the database itself but also a complete definition or description of the database structure and constraints.

online transaction processing (OLTP) applications

A fundamental role of multiuser DBMS software is to ensure that concurrent transactions operate correctly and efficiently.

The concept of a transaction has become central to many database applications

A transaction is an executing program or process that includes one or more database accesses, such as reading or updating of database records

Providing Storage Structures and Search Techniques for Efficient Query Processing

Auxiliary files called indexes are used for this purpose. Indexes are typically based on tree data structures or hash data structures

construction the database

Constructing the database is the process of storing the data on some storage medium that is controlled by the DBMS

A database can be of any size and complexity

For example, the list of names and addresses referred to earlier may consist of only a few hundred records, each with a simple structure.

Data Normalization

In a relational database, it is the process of organizing data to minimize redundancy

An example of a large commercial database is Amazon.com

It contains data for over 20 million books, CDs, videos, DVDs, games, electronics, apparel, and other items

manipulating the database

Manipulating a database includes functions such as querying the database to retrieve specific data, updating the database to reflect changes in the

Sharing of Data and Multiuser Transaction Processing

The DBMS must include concurrency control software to ensure that several users trying to update the same data do so in a controlled manner so that the result of the updates is correct

program-operation independence

The implementation (or method) of the operation is specified separately and can be changed without affecting the interface

An operation (also called a function or method) is specified in two parts

The interface (or signature) of an operation includes the operation name and the data types of its arguments (or parameters)

program-operation independence.

User application programs can operate on the data by invoking these operations through their names and arguments, regardless of how the operations are implemented

Restricting Unauthorized Access

When multiple users share a large database, it is likely that most users will not be authorized to access all information in the database.

An application program accesses the database

by sending queries or requests for data to the DBMS

To define this database, we must specify the structure of the records of each file

by specifying the different types of data elements to be stored in each record

The characteristic that allows program-data independence and program-operation independence

called data abstraction

The end users of a database may perform business transactions (for example, a customer buys a camera) or events may happen (for example, an employee has a baby) that

cause the information in the database to change

database system environment

hardware, software (Operating System, DBMS), People (administrators, designers, end-users), procedures, and data.

Databases and database technology impact

have a major impact on the growing use of computers. It is fair to say that databases play a critical role in almost all areas where computers are used, including business, electronic commerce

s, the DBMS should have the capability to control this redundancy

in order to prohibit inconsistencies among the files

A database management system (DBMS)

is a collection of programs that enables users to create and maintain a database.

A database

is a collection of related data.1

a data model

is a type of data abstraction that is used to provide this conceptual representation

The information stored in the catalog is called meta-data,

it describes the structure of the primary database

In order for a database to be accurate and reliable at all time

it must be a true reflection of the miniworld that it represents; therefore, changes must be reflected in the database as soon as possible

The database definition or descriptive information is also stored by the DBMS in the form of a database catalog or dictionary

meta-data

In object-oriented and object-relational databases, the abstraction process includes

not only the data structure but also the operations on the data. These operations provide an abstraction of miniworld activities commonly understood by the users.

Defining a database

nvolves specifying the data types, structures, and constraints of the data to be stored in the database

Denormalization

placing all the data together, we do not have to search multiple files to collect this data

Insulation between Programs and Data, and Data Abstraction

property program-data independence

Controlling Redundancy

redundancy in storing the same data multiple times leads to several problems.

First, there is the need to perform a single logical update

such as entering data on a new student—multiple times: once for each file where student data is recorded.

he data model uses logical concepts,

such as objects, their properties, and their interrelationships, that may be easier for most users to understand than computer storage concepts.

allowed to use certain privileged software,

such as the software for creating new accounts. Similarly, parametric users may be allowed to access the database only through the predefined canned transactions developed for their use

A view may be a subset of the database or it may contain virtual data

that is derived from the database files but is not explicitly stored

The DBMS is a general-purpose software system that facilitates

the processes of defining, constructing, manipulating, and sharing databases among various users and applications

controlled redundancy

to improve the performance of queries. For example, we may store Student_name and Course_number redundantly in a GRADE_REPORT file

data

we mean known facts that can be recorded and that have implicit meaning. For example, consider the names, telephone numbers, and addresses of the people you know

To construct the UNIVERSITY database

we store data to represent each student, course, section, grade report, and prerequisite as a record in the appropriate file.

to contstuct database we use

we use tables to construct any database

A DBMS should provide a security and authorization subsystem

which the DBA uses to create accounts and to specify account restrictions. Then, the DBMS should enforce these restrictions automatically

A DBMS provides users

with a conceptual representation of data that does not include many of the details of how the data is stored or how the operations are implemented

A database has the following implicit properties:..

■ A database is designed, built, and populated with data for a specific purpose. .