Views of data refer to the different ways to show the database management system to the user hiding its complexity.<\/p>\n
Levels of abstraction:<\/p>\n
The database is highly complex data. Developers hide the complexity of data structure which might not be familiar with the end-users. So, they provide abstract views of data. This is called data abstraction. There are 3 levels of abstraction. They are:<\/p>\n
Physical Level:<\/p>\n
It is called the lowest level of abstraction or internal level. It describes how the data is actually stored in the database. At this level, complex data structure details are shown.<\/p>\n
Logical Level:<\/p>\n
It is called the middle level of abstraction or conceptual level. It describes what data is stored in a database and also shows what relationship exists among those data.<\/p>\n
View Level:<\/p>\n
It is called the highest level of abstraction or external level. It describes the user interaction with database systems via application programs, that hide details of data types. It shows only a part of the entire database.<\/p>\n
Instances are defined as the data stored in a database at a particular moment of time. Schemas are the overall design of a database. The instances are actually copies of the instant data and information. But, on the other hand, schemas don’t contain any data or any information.<\/p>\n
Data independence refers to the mechanism of keeping the data independent from the user. Actually, meaning it allows users to make any kind of changes from one level of schemas without hampering other users at different levels of schemas.<\/p>\n
These three architecture makes the data independent from the users. Users can easily access data. However, the database is also convenient for the users from the view level, as they can get a simple user interface. Secondly, the logical level or conceptual level makes sure that if any ‘A’ user changes the structure of the table, then the other user cannot find the changes done by ‘A’. Thirdly, the physical level controls the view from users so they cannot view how data are actually stored in the database.<\/p>\n
They are called the set of statements for defining and manipulating the database. There are two types. They are:<\/p>\n
Data definition language:<\/p>\n
This language refers to the languages used to construct a database, modifying database objects like tables, indices, and users. Examples are queries like CREATE, MODIFY, REMOVE.<\/p>\n
Data manipulation language:<\/p>\n
This language refers to the languages used to ease users to manipulation of the database system. It includes operations like adding, deleting and modifying data in the database. Its main objective is to provide efficient human interaction with the system.<\/p>\n
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