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How are the internal external and conceptual schemas related to concept of logical and physical data independence?
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.
Is schema a logical structure or physical structure in oracle database?
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.
Difference between schema sub schema and instance in DBMS in detail?
the overall logical data base description is referred to as a schema. it is sometimes also referred to as an overall modal of the data, a conceptual modal of the data, a conceptual schema
How do different schema definition languages support the three schema architecture?
The three schema approach is used to build informational systems. The schema involves three different levels, which are the physical level, the conceptual level, and the external level.
2.5 What is the difference between logical data independence and physical data independence?
The logical data independence is the ability to modify a logical schema without making external view or application program change. The physical data independence is the ability to modify a physical schema without making external view or application prrogram change.
Explain the difference of internal external and conceptual schemas how are these schema layers related to the concept of logical and physical data independence?
External schemas allows data access to be customized (and authorized) at the level of individual users or groups of users. Conceptual (logical) schemas describes all the data that is actually stored in the database. While there are several views for a given database, there is exactly one conceptual schema to all users. Internal (physical) schemas summarize how the relations described in the conceptual schema are actually stored on disk (or other physical media). External schemas provide logical data independence, while conceptual schemas offer physical data independence.
What Logical data independence and physical data?
Logical data independence refers to the ability to modify the conceptual schema without changing the external schemas or application programs. In contrast, physical data independence allows changes to the internal schema – like indexes and storage structures – without affecting the conceptual or external schemas.
What are the 3 views of dbms?
A Database has three views. The External Schema: What the end user sees. The Internal Schema: What the programmers of the program see. The Conceptual Schema: The basic plan of the database. Most of the time this is in paper form as a Conceptual Schema Diagram (CSD)
What is global conceptual schema?
The enterprise view of the data is described by the global conceptual schema (GCS), which is global because it describes the logical structure of the data at all the sites.
What is schema and sub-schema?
The schema is the physical arrangement of the data as it appears in the DBMS. The subschema is the logical view of the data as it appears to the application program.
Mapping in DBMS architecture?
We know that three view-levels are described by means of three schemas. These schemas are stored in the data dictionary. In DBMS, each user refers only to its own external schema. Hence, the DBMS must transform a request on. a specified external schema into a request against conceptual schema, and then into a request against internal schema to store and retrieve data to and from the database. The process to convert a request (from external level) and the result between view levels is called mapping. The mapping defines the correspondence between three view levels. The mapping description is also stored in data dictionary. The DBMS is responsible for mapping between these three types of schemas. There are two types of mapping. (i) External-Conceptual mapping (ii) Conceptual-Internal mapping External-Conceptual Mapping An external-conceptual mapping defines the correspondence between a particular external view and the conceptual view. The external-conceptual mapping tells the DBMS which objects on the conceptual level correspond to the objects requested on a particular user's external view. If changes are made to either an external view or conceptual view, then mapping must be changed accordingly. Conceptual-Internal Mapping The conceptual-internal mapping defines the correspondence between the conceptual view and the internal view, i.e. database stored on the physical storage device. It describes how conceptual records are stored and retrieved to and from the storage device. This means that conceptual-internal mapping tells the DBMS that how the conceptual! records are physically represented. If the structure of the stored database is changed, then the mapping must be changed accordingly. It is the responsibility of DBA to manage such changes.
Discuss the basic differences between external schema conceptual schema and internal schema?
The internal schema describes how the data will be physically stored and accessed, using the facilities provided by a particular DBMS. For example, the data might be organized so that all the insurance policies belonging to a given customer were stored close together, allowing them all to be retrieved into the computer's memory in a single operation. The conceptual schema (sometimes called the logical schema) describes the stored data in terms of the data model of the DBMS. In a relational DBMS, the conceptual schema describes all relations that are stored in the database The external schemasspecify views that enable different users of the data to see it in different ways. As a simple example, some users of policy data might not require details of the commission paid. By providing them with a view that excludes the Commission Rate column, we would not only shield them from unwanted (and perhaps unauthorized) information, but also insulate them from changes that might be made to the format of that data.by:mohammed abu Lamdy
