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DBMS Three-Schema Architecture and Data Independence
WHAT IS DBMS ?
- To be able to carry out operations like insertion, deletion and retrieval, the database needs to be managed by a substantial piece of software; this software is usually called a Database Management System(DBMS).
- A DBMS is usually a very large software package that enables many different tasks including the provision of facilities to enable the user to access and modify information in the database.
- Data Description Languages (DDL) and Data Manipulation Languages (DML) are needed for manipulating and retrieving data stored in the DBMS. These languages are called respectively.
An architecture for database systems, called the three-schema architecture was proposed to help achieve and visualize the important characteristics of the database approach.
THE THREE-SCHEMA ARCHITECTURE:
The goal of the three-schema architecture is to separate the user applications and the physical database. In this architecture, schemas can be defined at 3 levels :
1. Internal level or Internal schema : Describes the physical storage structure of the database. The internal schema uses a physical data model and describes the complete details of data storage and access paths for the database.
2. Conceptual level or Conceptual schema : Describes the structure of the whole database for a community of users. It hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints. Implementation data model can be used at this level.
3. External level or External schema : It includes a number of external schemas or user views. Each external schema describes the part of the database that a particular user is interested in and hides the rest of the database from user. Implementation data model can be used at this level.
IMPORTANT TO REMEMBER :
Data and meta-data
- three schemas are only meta-data(descriptions of data).
- data actually exists only at the physical level.
Mapping
- DBMS must transform a request specified on an external schema into a request against the conceptual schema, and then into the internal schema.
- requires information in meta-data on how to accomplish the mapping among various levels.
- overhead(time-consuming) leading to inefficiencies.
- few DBMSs have implemented the full three-schema architecture.
DATA INDEPENDENCE
The disjointing of data descriptions from the application programs (or user-interfaces) that uses the data is called data independence. Data independence is one of the main advantages of DBMS. The three-schema architecture provides the concept of data independence, which means that upper-levels are unaffected by changes to lower-levels. The three schemas architecture makes it easier to achieve true data independence. There are two kinds of data independence.
- Physical data independence
* The ability to modify the physical scheme without causing application programs to be rewritten.
* Modifications at this level are usually to improve performance.
- Logical data independence
* The ability to modify the conceptual scheme without causing application programs to be rewritten.
* Usually done when logical structure of database is altered.
Logical data independence is harder to achieve as the application programs are usually heavily dependent on the logical structure of the data. An analogy is made to abstract data types in programming languages.
1.) What is a Database?
The Database are designed to offer an organized mechanism for storing , managing and retrieving information. They do so through the use of tables. If you're familar with spreadsheets like Microspft Excel , you're probably already Accustomed to storing data in tabular form. It's not much of a streatch to make the leap from spreadsheets to database.
2.) What are the kinds of Database?
In computing , a database can be defined as a structured collection of records or data that is stored in a computer so that a program can consult it to answer queries.
3.)
There are two approaches for developing any database, the top-down method and the bottom-up method. While these approaches appear radically different, they share the common goal of uniting a system by describing all of the interaction between the processes
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different types of realist and non-realist approaches?
Is the oldest of all the approaches used to design an operating system?
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What is the best description of a database management system?
Database Management System is a software package with computer programs that control the creation, maintenance, and the use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated collection of data records, files, and other database objects. A DBMS allows different user application programs to concurrently access the same database.
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What are approaches to curriculum design?
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Design of the database (Database Design) refers to a given application environment, optimize the structure of the database, the database and applications, which can efficiently store data to meet the application needs of various user information needs and processing requirements). At www. myelibrary.net.In you can clearly understand what is the database design.
Design a Web Database?
form_title=Design a Web Database form_header=Hire a developer to design a database to complement your business. What kind of business is the database design for?=_ What will you need the database design to offer?=_ Will you need ongoing support for the design?= () Yes () No () Not Sure
Database Design?
form_title=Database Design form_header=Transform your company by incorporating a new database design. What program will the database be used with?=_ Please explain what you will be using the database for?="" Do you have a database that you're already using?= () Yes () No
discus the main approaches for managing the design of database system that has mutliple user view?
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Marketing Database Design?
form_title=Marketing Database Design form_header=Successful marketing comes from a well-designed database. Have one designed by a professional. What does your business do?=_ What is your budget for the database design?=_ Who is your target audience?=_ When does the database need to be completed?=_
How is database structured?
That depends on the type of database it is and the design of the Database Annalist.
What are the principles of database development?
The main principles of database development is to create user friendly computer applications with excellent quality. Database design is useful in many different ways and areas.
Custom Database Design?
form_title=Custom Database Design form_header=Design, develop and manage the database that fits your business needs. What do you need the database to offer?=_ Who will have access to the database?=_ Is this database for the internal or external public?= {(),Internal,External} Do you need the new database to integrate with a current system?= () Yes () No () Not Sure
Database Design Tools?
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Logical database design is the process of designing the database at a conceptual level as opposed to a physical level. There are many advantages of conceptual database design, such as the ability to design the database without having to commit to a particular database management system, to produce a document that is readable and understandable to everyone in the company (not just the database person) and to produce an overall design document that can be saved as a part of the documentation of the database for future enhancement, maintenance and support work. Logical database design produces documents for use in the same way that architects produce blueprints for building purposes.
