Now, a question arises what is the need to change the data schema at a logical or conceptual level? Logical data independence describes the degree up to which the logical or conceptual schema can be changed without modifying the external schema. Data independence can be classified as shown below: Logical Data Independence: So, the programmers work at the logical level and even the database administrator also operates at this level.Īt the view level, the users have the set of applications which they use to retrieve the data they are interested in.ĭata independence defines the extent to which the data schema can be changed at one level without modifying the data schema at the next level. This is the physical or internal level and is hidden from the programmers but the database administrator is it aware of it.Īt the logical level, the programmers define the entity sets and relationship among these entity sets using a programming language like SQL. Now, the entity sets Student, Lecturer, Department, Course will be stored in the storage as the consecutive blocks of the memory location. Now, what entity sets would be involved? Student, Lecturer, Department, Course and so on… We have to create a database of a college. To understand it more clearly let us take an example: In the figure above you can clearly distinguish between the three levels of abstraction. The figure below describes the three-schema architecture of the database: Here, the user retrieves the information using different application from the database. The view level can describe many views of the same data. It exhibits the data in which the user is interested. It is the highest level of data abstraction and exhibits only a part of the whole database. It is the developer and database administrator who operates at the logical or the conceptual level.ģ. As users are restricted to access some particular parts of the database. Well adding constraints to the view of data adds the security. Here, the data is stored in the form of the entity set, entities, their data types, the relationship among the entity sets, user operations performed to retrieve or modify the data and certain constraints on the data. Only the database administrator operates at this level. The physical level shows the data abstraction at the lowest level and it has complex data structures. It also describes how the data can be accessed. The physical or the internal level schema describes how the data is stored in the hardware. The three-schema architecture defines the view of data at three levels: So, the user never has to be concerned regarding the internal storage of the database and it has a simplified interaction with the database system. The main objective of this architecture is to have an effective separation between the user interface and the physical database. To achieve data abstraction, we will discuss a Three-Schema architecture which abstracts the database at three levels discussed below: Three-Schema Architecture: It is done because many of the users interacting with the database system are not that much computer trained to understand the complex data structures of the database system. Content: View of Data in DBMSĭata abstraction is hiding the complex data structure in order to simplify the user’s interface of the system. In this section, we will discuss the view of data in DBMS with data abstraction, data independence, data schema in detail. While changing the data schema at one level of the database must not modify the data schema at the next level. There is one more feature that should be kept in mind i.e.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |