![]() After the conceptual schema undergoes a logical reorganization, application programs that reference the external schema constructs must work as before. Only the view definition and the mappings need be changed in a DBMS that supports logical data independence. In the last case, external schemas that refer only to the remaining data should not be affected For example, the external schema of Figure 1.5(a) should not be affected by changing the GRADE_REPORT file (or record type) shown in Figure 1.2 into the one shown in Figure 1.6(a). We may change the conceptual schema to expand the database (by adding a record type or data item), to change constraints, or to reduce the database (by removing a record type or data item). Logical data independence is the capacity to change the conceptual schema without having to change external schemas or application programs.We can define two types of data independence: What is Data Independence in DBMS The three-schema architecture can be used to further explain the concept of data independence, which can be defined as the capacity to change the schema at one level of a database system without having to change the schema at the next higher level. Please write comments if you find anything incorrect, or if you want to share more information about the topic discussed above.What is Data Independence in DBMS Data Independence This article is contributed by Avneet Kaur. These changes may include insertion or deletion of attributes, altering table structures entities or relationships to the logical schema, etc. The user view of the data would not be affected by any changes to the conceptual view of the data. Logical level data independence: It refers characteristic of being able to modify the logical schema without affecting the external schema or application program. Altering indexes or using alternative file organization techniques etc. ![]() Modifying data structures used for storage.These alterations or modifications to the physical structure may include: ![]() Changing from sequential to random access files is one such example. Physical level data independence: It refers to the characteristic of being able to modify the physical schema without any alterations to the conceptual or logical schema, done for optimization purposes, e.g., the Conceptual structure of the database would not be affected by any change in storage size of the database system server. We have namely two levels of data independence arising from these levels of abstraction : The main purpose of data abstraction is to achieve data independence in order to save the time and cost required when the database is modified or altered. Users can just view the data and interact with the database, storage and implementation details are hidden from them. Multiple views of the same database may exist. Tables and relations are used to store data. Users view data in the form of rows and columns. This level exists to ease the accessibility of the database by an individual user. Only a part of the actual database is viewed by the users. View: This is the highest level of abstraction.
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