Database Management System (DBMS)

Database Models in DBMS

2012-08-13T11:28:00.002-07:00

Data Models

Database is made in 1960, is triggered when the need for a system management information flexible. The data model is a set of terms that are used for the database structure can be described. An image or a data model describes how data should be prepared to serve a particular purpose. The data model represents the data elements required, and the data should look like. However, it is misleading to discuss data models, as if the data type of the model, and equally wrong to speak of him, as if used for a purpose.

There are three different types of models and advanced data generated for the purpose of the database to the information system itself. The data must be identified first as a conceptual data model can be essentially a set of technical specifications and independent data are used to discuss the initial needs of the stakeholders of the company.

Data modeling techniques are used :-

• To control data as a resource ( migrate, merge, data quality).
• For designing computer databases.
• To better cope with modify, by allowing to make changes into the model, that will automatically make changes in the database and programs.

Data models can be broadly illustrious into 3 main categories:-

1) High-level or Conceptual Data Models : It provides idea that are close to the way many users recognize data.

2) Low Level or Physical Data Models:- It provides idea that explain the details of how data is stored in the computer.

3) Representational or Implementation Data Models: It provides idea that can be understand by end users. These hide some facts of data storage but can be implemented on a computer system directly.

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About Structured Query Language (SQL)

2012-08-10T13:38:00.001-07:00

SQL

Structured Query Language (SQL) is a commonly used programming language for effective with relational databases. As its full name (Structured Query Language) shows, SQL is liable for querying and editing information stored in a convinced database management system. Though the SQL comes in lots of flavors, for example besides the standard SQL syntax, the Oracle databases also operate their proprietary PL/SQL, similarly Microsoft SQL Server operate their Transact-SQL. All of these variations, through proprietary, are stand upon the industry standard ANSI SQL.

Therefore, SQL is considered to be planned at a higher conceptual level of operation than procedural languages because the lower level logical and physical operations are not particular and are determined by the SQL engine or server process that complete it. The SQL UPDATE command is used to make modification to existing database tables and records. All the required Structured Query Language commands in a related RDBMS can typically be executed during an SQL command line interface (CLI).

Database Models :-

A data model comprises

1. A data structure
2. A set of integrity constraints
3. Operations related with the data structure

Examples of data models include :-

1. hierarchic
2. network
3. relational

What Can SQL do?

1. SQL can retrieve data from a database
2. SQL can update records in a database
3. SQL can create new databases
4. SQL can create views in a database

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Relational Database Management System (RDBMS)

2012-08-10T13:27:00.000-07:00

RDBMS

Combine separate files related (tables) of a series is maintained, but the elements of database queries and reports, data files, if necessary. concept Edgar Codd in 1970, was selected for a user to adapt to ad hoc data. The majority of companies in the management system database (DBMS), Oracle, DB2, SQL Server, MySQL, etc., related to a DBMS (RDBMS) is (see DBMS), including. Applications of modern databases and commercial open-source relational in nature. The main features of relational database tables to store data in a way that can be used, and maintain, however, some data Relationships.

Universal report: -

The report is, essentially, a universal condition, and he said It is possible, a large table, while the data store. In a sense, a universal relation, "before" fully normalized relational schema. It is also assumed that the semantic attributes of the various reports in the same way. As a result, many Columns can be NULL. But the thought experiment, which is perfectly fine.

Associations: -

Interviews in some local or remote communities are usually instances of SQL CONNECT, the display server. The current MIB does not reveal there are individual companies, the union and the board of Apple dbmsSvrInfoTable counters. There are also connections between servers and databases. obvious Possible relations and media.

. A database: 1 Server
. A database: the number of servers
. Many database: 1 Server
. Many database server

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XML (Extensible Markup Language)

2011-11-20T05:29:00.000-08:00

Definite by the WWW Consortium (W3C)
Initially intended as a document markup language not a database language
The ability to denote new tags and to produce nested tag structures made XML a immense way to switch data, not just documents
XML has grown to be the basis for all innovative generation data interchange formats.
A wide diversity of tools is existing for parsing, browsing and querying XML documents/data

Database Administrator

2011-11-20T05:25:00.000-08:00

Synchronize all the actions of the database system; the database administrator has a superior considerate of the enterprise’s information resources and requirements.

Database administrator's responsibilities include:-

Schema definition
Storage structure and admittance method explanation
Schema and physical organization alteration
Yielding user authority to admittance the database
Denote integrity constraints
Acting as liaison with users
Watch out performance and responding to alter in requirements

Database Users

2011-11-20T05:23:00.000-08:00

Users are distinguished by the way they expect to interrelate with the system.

Application programmers – interrelate with system all the way through DML calls
Sophisticated users – form requests in a database query language
Specialized users – write dedicated database applications that do not fit into the traditional data processing framework
Naive users – appeal to one of the permanent application programs that have been written formerly

Examples, people accessing database in excess of the web, bank tellers, clerical staff

Database Architecture

2011-11-20T05:21:00.000-08:00

The architecture of database systems is greatly prejudiced by the underlying computer system on which the database is running:

Centralized
Client-Server
Parallel (Multiprocessor)
Distributed

Transaction Management

2011-11-20T05:13:00.000-08:00

A Transaction is a compilation of operations that carry out a single logical function in a database application.

Transaction management part ensures that the database remains in a consistent (correct) state even with system failure (e.g., power failures and operating system crashes) and transaction failures.

Concurrency control manager controls the interface between the concurrent transactions, to make certain the consistency of the database.

Database Design

2011-11-20T05:12:00.000-08:00

The process of designing the general structure of the database:-

Logical Design – decide on the database schema. Database design necessitates that we find a “good” assortment of relation schemas.

Business decision – What attributes should we evidence in the database?

Computer Science decision – What relation schemas should we have and how should the attributes be disseminated between the various relation schemas?

Physical Design – Deciding on the physical layout of the database

Structured Query Language (SQL)

2011-11-20T05:10:00.000-08:00

SQL: Extensively used nonprocedural language

Example: Find the name of the customer with customerid 192837465

Select customer.customer_name

from customer

where customer.customer_id = ‘192837465’

Example: Find the balances of all accounts detained by the customer with

customerid 192837465

Select account.balance

From depositor, account

where depositor.customer_id = ‘192837465’ and

depositor.account_number = account.account_number

Application programs commonly access databases through one of:-

Language extension to consent to embedded SQL
Application program interface (e.g., ODBC/JDBC) which permit SQL
Queries to be sent to a database

Data Definition Language (DDL)

2011-11-20T05:04:00.000-08:00

Specification notation for significant the database schema

Example: create table account (

Account number char (10),

Balance integer)

DDL compiler produces a set of tables stored in a data dictionary.

Data dictionary contains metadata (i.e., data about data)
Database schema
Data storage and definition language
Specifies the storage structure and admittance methods used

Integrity constraints

Domain constraints

Referential integrity (references constraint in SQL)

Assertions

Authorization

Data Manipulation Language (DML)

2011-11-20T04:58:00.000-08:00

Data Manipulation Language is a language for accessing and manipulate the data organized by the apposite data model.
DML also known as query language.

Two classes of languages:-

Procedural – user specify what data is required and how to get those data
Declarative (nonprocedural) – user specifies what data is required without specify how to get those data

SQL is the most broadly used query languages

Data Models?

2011-11-20T04:54:00.000-08:00

Data Model is a collection of tools for describing:-

Data
Data relationships
Data semantics
Data constraints

Relational model
Entity Relationship data model (generally for database design)
Object based data models (Object-oriented and Object relational)
Semi structured data model (XML)

Other older models:-

Network model
Hierarchical model

Instance and Schema:-

2011-11-20T04:46:00.000-08:00

Similar to types and variables in programming languages:-

Schema:– The logical structure of the database

Example: The database consists of information about a set of clientele and accounts and the connection between them)

Analogous to type information of a variable in a program.

Physical schema: Database design at the physical level

Logical schema: Database design at the logical level

Instance:- The actual content of the database at a particular point in time

Analogous to the value of a variable.

Physical Data Independence:– the ability to modify the physical schema without Changing the logical schema

Applications depend on the logical schema

In general, the interfaces between the various levels and components should be well defined so that changes in some part do not seriously influence others.

Levels of Abstraction:-

2011-11-20T04:42:00.000-08:00

Physical level: Describes how a record (e.g., customer) is stored.

Logical level: describes data stored in database, and the relations among the data.

type customer = record

customer_id : string;

customer_name : string;

customer_street : string;

customer_city : integer;

end;

View level: application programs hide details of data types. Views can also hide information (such as an employee’s salary) for security Purposes

Purpose of Database Systems:-

2011-11-20T04:38:00.000-08:00

Drawbacks of using file systems (cont.)

1) Atomicity of updates

Failures may leave database in an inconsistent state with part
Updates carried out

Example: Transfer of funds from one account to another should

either complete or not happen at all

2) Concurrent access by multiple users

Concurrent accessed required for presentation
Uncontrolled concurrent accesses can lead to inconsistency

Example: Two people reading a balance and updating it at the Similar time

3) Security problems

Hard to provide user access to some, but not all, data

Database systems offer solutions to the entire above problem

What is DBMS?

2011-11-19T04:32:00.000-08:00

DBMS contains information about a particular enterprise
Collection of interrelated data
Set of programs to access the data
An environment that is both convenient and efficient to use

Database Applications:-

Banking: all transactions
Airlines: reservations, schedules
Universities: registration, grade
Sales: customers, products, purchases
Online retailers: order tracking, customized recommendation
Manufacturing: production, inventory, orders, supply chain
Human resources: employee records, salaries, tax deductions
Databases touch all aspects of our live