You might ask Why we need View when we can use SELECT in this case? What is Data Independence?ĭata independence is an advantage of levels of abstraction in the database management system. One for the students and the other one for the teachers with the appropriate set of data. Students cannot view the teacher's salary because the data is irrelevant to them.īut teachers can view each and every detail of the students as well as their own data. This is easier to understand with an example.Įxample: Students only need to view their score, courses, attendance and other details that are relevant fo them. We hide the data from a view that is irrelevant to them. The application program (which general users use) tries to view that data according to the user role. This is the last level of abstraction in DBMS. Here we define the structure of the database and relationships among the data. The project guide will only contain the entry present in TEACHER_ID. Take the table of teachers that contains TEACHER_ID, NAME, SALARY and table of students that contains STUDENT_ID, NAME, COURSE, PROJECT_NAME, PROJECT_GUIDE and so on. But what data we are going to store? What are their types? How they will be related to each other?Īt the logical level, we will define all of them. We need to store data about teachers and students. In simple words, we create the blueprint of the database at the logical level.Įxample: Take the example of the university database. It defines the overall structure of the database and relationships between the data. The logical level contains the data that is actually stored in the database. It describes the data stored in the database and relationship among them. This is the second level of abstraction in DBMS. The access modes like sequential or random access, file organisation methods like B+ tree and indexing and hashing are implemented at this level. It depends on the hardware and OS of the system. The physical level of abstraction actually contains the database storage files and binary files which is the actual storage of the database system. DBA decides certain things like the drive where the data will be actually stored in the system and whether the storage will be centralized or decentralized. The Database Administrator (DBA) manages the physical level. Physical level deals with the storage of the data for the whole database system. It is a low-level representation of the database. This is the first or lowest level of abstraction which describes how a record is actually stored in the system memory. Three levels of data abstraction in database Physical level There are three levels of data abstraction in DBMS which reduce the complexity of the database and also provide data independence at each level. The information like how and where Google stores its data is irrelevant for us that's why the information is hidden from us. The type of information that is relevant and irrelevant depends upon the level itself which we will see later in the post.ĭata abstraction in DBMS is very helpful in dealing with the complex database system because it breaks the problem into subproblems which makes it easy to manage.Įxample: We use Google daily but we have no ideas of its data storage. The process of hiding irrelevant information at each level of a database is known as data abstraction. This helps us to focus on a specific level only and easy to manage the whole database system. Data abstraction is the best way to keep a database system easy to manage by breaking it into levels and abstract (hide) irrelevant details at each level. Database systems are complex in nature and we need to keep it as simple as possible.
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