A logical unit of data is a virtual representation of data while a physical unit of data is the actual storage of data on a physical device. The logical unit of data is how data is organized and manipulated from a software perspective, while the physical unit of data is how data is stored on hardware such as disks or memory.
A schema separates the physical aspect of data storagefrom the logical aspects of data representation.
It is generally considered more difficult to achieve logical data independence compared to physical data independence. Logical data independence involves separating the conceptual structure of the data from the physical storage aspects, which can be complex depending on the database design. Physical data independence primarily deals with shielding the application from changes in the storage structure, which is usually more straightforward to achieve.
Logical data independence is considered more difficult than physical data independence because it involves changes to the conceptual schema and external schema, which are more closely tied to the way data is organized and viewed in the application. Physical data independence, on the other hand, deals with changes to the internal schema, which is more abstract and can be modified with less impact on the overall system.
The three levels of data abstraction in a DBMS are physical, logical, and view. Physical level: Describes how data is stored in the database, including details like data storage and access paths. Logical level: Focuses on the structure of the data in the database, including schemas, tables, and relationships. View level: Represents how users view the data, providing a customized and simplified representation of the data to different user groups.
Logical data independence refers to the ability to change the conceptual schema without affecting the external schema or application programs. Physical data independence, on the other hand, refers to the ability to change the physical schema without affecting the conceptual schema. This allows changes in the storage structure or access methods without changing how data is viewed or accessed by applications.
what is physical datd independence
Logical data independence is considered more difficult than physical data independence because it involves changes to the conceptual schema and external schema, which are more closely tied to the way data is organized and viewed in the application. Physical data independence, on the other hand, deals with changes to the internal schema, which is more abstract and can be modified with less impact on the overall system.
the logical data independence is hard to achieve because all the manipulation is belonging in logical data independence but in physical data independence only show the physical view .
A schema separates the physical aspect of data storagefrom the logical aspects of data representation.
A schema separates the physical aspect of data storagefrom the logical aspects of data representation.
Logical file is a type of file that provides a view of the data stored into the Physical file. It does not contain data. A logical file contains only an index to the data stored into the physical file.
difference between physical and logical data flow diagrams.
The logical database is how the data is percieved in the tables, the way the data is actually stored on the storage medium is the physical view of the database.
Logical data independence refers to the ability to change the conceptual schema without affecting the external schema or application programs. Physical data independence, on the other hand, refers to the ability to change the physical schema without affecting the conceptual schema. This allows changes in the storage structure or access methods without changing how data is viewed or accessed by applications.
Physical data structure: This is the physical equipment involved in the network eg router, cabling etc). Logical data structure: This is how the information flows internally and externally (the transfer of information from one node to another on the network).
The logical view presents data as they would be perceived by end users or business specialists, whereas the physical view shows how data are actually organized and structured on physical storage media.
- An MMU (memory management unit) generates physical address. - A CPU (central processing unit) generates a logical address.