Physical data structures are how data is organized on a hardware storage device, and therefore how they appear to the computer. Logical or virtual data structures are software-based objects, and how the user or program sees it. Although many file systems use a type of linked list format for storing information, a linked list is used for both hardware and software purposes, and therefore it cannot fall under either the physical or virtual data structure classification.
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For a physical Data Flow Diagram you explore into the logical DFD. for example, if you have a data flow arrow declared as "customer information" now the physical DFD would include in that data flow arrow "customer information = customer_name + customer_address". something along these lines Physical DFD shows how various functions are performed and who does them but Logical DFD strips away all physical constraints but does not restrict physical happenings from taking place.
logical data : refer to the immunity of the external scheme towards changes in the conceptual scheme.physical data: refer to the immunity of the conceptual scheme towards changes in the internal scheme.
A Physical Data Flow Diagram is a diagram showing howparticular functions are performed within the data flow as opposed to a Logical DFD which only shows what functions are performed.
Linear data structure is used to convert the logical address to physical address .Stack is used in this and the various conversion such as postfix,prefix and infix notation are come in this
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.
Physical structure refers to the actual layout of data on the disk, including sectors, tracks, and cylinders. Logical structure refers to how the operating system organizes and accesses data on the disk, such as partitions, file systems, and directories.
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The internal schema represents the physical storage structure of data, the external schema represents how different users view the data, and the conceptual schema defines the logical structure of the entire database. Logical data independence means that the conceptual schema can change without affecting the external schemas, while physical data independence means that changes in the physical storage structures do not affect the conceptual or external schemas.
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.
the schema can be termed either conceptual or logical or physical. But mostly speaking, the term schema is used to refer to a logical structure.
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.
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.
A logical database refers to the way data is organized, modeled, and accessed by users, focusing on the structure and relationships of data. In contrast, a physical database relates to how data is actually stored on disks, including indexes, partitions, and access paths designed for efficient data retrieval and storage.
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.