What is Mapping bet internal conceptual and external views?

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)

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 is RDBMS explain its architecture.?

RDBMS : Architecture of a Database Management SystemThe architecture of a database management system can be broadly divided into three levels :a. External levelb. Conceptual levelc. Internal levelThe External LevelThis is the highest level, one that is closest to the user. It is also called the user view. The user view is different from the way data is stored in the database. This view describes only a part of the actual database. Because each user is not concerned with the entire database, only the part that is relevant to the user is visible. For example, end users and application programmers get different external views.For example, an instructor will view the database as a collection of students and courses offered by the university. An administrator will view the database as a collection of records on the stock of course material provided by the university. The instructor is concerned with only a portion of database that is relevant to the instructor and the administrator is concerned with only the portion of database that is relevant to the administrator. These portions of database, which are viewed, by the instructor and administrator are reffered as their user's view or external view.Each user uses a language to carry out database operations. The application programmer uses either a conventional third-generation language, such as COBOL or C, or a fourth-generation language specific to the DBMS, such as visual FoxPro or MS Access.The end user uses a query language to access data from the database. A query language is a combination of three subordinate language :§ Data Definition Language (DDL)§ Data Manipulation Language (DML)§ Data Control Language (DCL)The data definition language defines and declares the database object, while the data manipulation language performs operations on these objects. The data control language is used to control the user's access to database objects.The Conceptual LevelThis level comes between the external and the internal levels. The conceptual level represents the entire database as a whole, and is used by the DBA. This level is the view of the data "as it really is". The user's view of the data is constrained by the language that they are using. At the conceptual level, the data is viewed without any of these constraints.The Internal LevelThis level deals with the physical storage of data, and is the lowest level of the architecture. The internal level describes the physical sequence of the stored records.Following is an example of the three levels :ExternalCout

Explain the layered architecture of a DBMS?

The ANSI/SPARC architecture is divided into three levels, known as the internal, conceptual, and external levels.The internal level is the one closest to physical storage, i.e., it is the one concerned with the way the data is physically stored.The external level is the one closest to the users i.e., it is the one concerned with the way the data is viewed by individual users.The conceptual level is a "level of indirection" between the other two.If the external level is concerned with individual user views, then the conceptual level is concerned with a community user view. In other words, there will be many distinct external views, each consisting of a more or less of a abstract representation of some portion of the total database, and there will be precisely one conceptual view, consisting of a similarly abstract representation of the database in it's entirely. Likewise, there will be precisely one internal view, representing the total database as physically stored. When we describe some representation as abstract here, we merely mean that it involves user-oriented constructs such as logical records and fields instead of machine-oriented constructs such as bits and bytes.The external level: The external level is the individual user level. A given user can be either an application programmer or an end user of any degree of sophistication. The DBA is an important special case. Unlike other users, however, the DBA will need to be interested in the conceptual and internal levels also.The conceptual level: The conceptual view is a representation of the entire information content of the database, again (as with an external view) in a form that is somewhat abstract in comparison with the way in which the data is physically stored. It will also be quite different, in general, in the way from which any particular user views the data. Broadly speaking, the conceptual view is intended to be the view of the data "as it really is", rather than as users are forced to see it by the constraints of the particular language or hardware they might be using.The internal level: The third level of the architecture is the internal level. The internal view is a low level representation of the entire database; it consists of many occurrences of each of many types of internal record. "Internal record" is the ANSI/SPARC term for the construct that we have been calling a stored record.

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

Explain the architecture of DBMS?

the architecture of dbms contains three levels 1/ external level:different users views of the database,shows relevant data for a particular user. 2/conceptual level:global view pf the database;describes what data is stored and its relationships. 3/internal level:physical representation of the database on the computer, Describes how the data is stored in the database.

Descripe the architecture of a DBMS in terms of 3 schema architecture?

We now discuss a conceptual framework for a DBMS. Several different frameworks have been suggested over the last several years. For example, a framework may be developed based on the functions that the various components of a DBMS must provide to its users. It may also be based on different views of data that are possible within a DBMS. We consider the latter approach.A commonly used views of data approach is the three-level architecture suggested by ANSI/SPARC (American National Standards Institute/Standards Planning and Requirements Committee). ANSI/SPARC produced an interim report in 1972 followed by a final report in 1977. The reports proposed an architectural framework for databases. Under this approach, a database is considered as containing data about an enterprise. The three levels of the architecture are three different views of the data:External - individual user viewConceptual - community user viewInternal - physical or storage viewThe three level database architecture allows a clear separation of the information meaning (conceptual view) from the external data representation and from the physical data structure layout. A database system that is able to separate the three different views of data is likely to be flexible and adaptable. This flexibility and adaptability is data independence that we have discussed earlier.We now briefly discuss the three different views.The external level is the view that the individual user of the database has. This view is often a restricted view of the database and the same database may provide a number of different views for different classes of users. In general, the end users and even the applications programmers are only interested in a subset of the database. For example, a department head may only be interested in the departmental finances and student enrolments but not the library information. The librarian would not be expected to have any interest in the information about academic staff. The payroll office would have no interest in student enrolments.The conceptual view is the information model of the enterprise and contains the view of the whole enterprise without any concern for the physical implemenation. This view is normally more stable than the other two views. In a database, it may be desirable to change the internal view to improve performance while there has been no change in the conceptual view of the database. The conceptual view is the overall community view of the database and it includes all the information that is going to be represented in the database. The conceptual view is defined by the conceptual schema which includes definitions of each of the various types of data.The internal view is the view about the actual physical storage of data. It tells us what data is stored in the database and how. At least the following aspects are considered at this level:Storage allocation e.g. B-trees, hashing etc.Access paths e.g. specification of primary and secondary keys, indexes and pointers and sequencing.Miscellaneous e.g. data compression and encryption techniques, optimisation of the internal structures.Efficiency considerations are the most important at this level and the data structures are chosen to provide an efficient database. The internal view does not deal with the physical devices directly. Instead it views a physical device as a collection of physical pages and allocates space in terms of logical pages.The separation of the conceptual view from the internal view enables us to provide a logical description of the database without the need to specify physical structures. This is often called physical data independence. Separating the external views from the conceptual view enables us to change the conceptual view without affecting the external views. This separation is sometimes called logical data independence.Assuming the three level view of the database, a number of mappings are needed to enable the users working with one of the external views. For example, the payroll office may have an external view of the database that consists of the following information only:Staff number, name and address.Staff tax information e.g. number of dependents.Staff bank information where salary is deposited.Staff employment status, salary level,leave information etc.The conceptual view of the database may contain academic staff, general staff, casual staff etc. A mapping will need to be created where all the staff in the different categories are combined into one category for the payroll office. The conceptual view would include information about each staff's position, the date employment started, full-time or part-time, etc etc. This will need to be mapped to the salary level for the salary office. Also, if there is some change in the conceptual view, the external view can stay the same if the mapping is changed.

What is a external mirror?

An external mirror is a mirror that points outward, creating views of whatever it is reflecting

What is external schema?

The role of the external schema is to support user views of data and thus to provide programmers with easier data access

What are the external and internal factors affecting the Human Resource Planning?

external factors affecting Human Resource Planning - government legislation -job mobility factors -population shifts -economic cycles and condition -geographical concerns -educational levels of workers -technological changes -changes in social views -political changes -international events

Can the epiphyseal plate be seen in both the external and cutaway views of an adult long bone?

False

What is an X ray procedure that reveals cross-sectional views of internal structural damage or problems in the brain?

There are two procedures that are non invasive to check for internal and structural problems of the brain. The x-ray procedure that involves cross-sectional views of these internal brain structures is a CAT scan.