DB Projects Help >> DBMS architecture & data independence
Collection control techniques are complicated programs which were often formulated and optimized over years. From the perspective of the customer, however, most of them have a quite identical primary structure. The conversation of this primary structure shall help to comprehend the network with information which and the introduction ally to this element postulated 'data independence' of the database technique.
Knowing about the conceptual and the made sensible construction (discussed in model Collection Models, Plans and Instances this model describes two additional schemes - the exterior construction and the inner construction - which help to understand the DBMS construction.
An exterior details construction represents the details about the customer perspective of particular people (single people and customer groups) and the particular techniques and demands connected with these details. (Translated) (ZEHNDER 1998)
The inner details construction represents the content of the details and the required service features which is used for the function of the DBMS. (Translated) (ZEHNDER 1998)
Therefore, the inner construction represents the details from a perspective very close to the computer or system in general. It does the sensible construction with details specialized aspects like storage space techniques or help functions for more overall performance.
The right hand side of the manifestation above is also called the three-scheme architecture: inner, sensible and external scheme.
While the inner construction represents the actual collection of the details and the use of the storage space, the sensible construction (derived from the conceptual scheme) represents the basic engineering of the details construction. The exterior construction of a particular request, generally, only features that part of the sensible construction which is relevant for its request. Therefore, a database has exactly one inner and one sensible construction but may have several exterior schemes for several programs using this database.
The aim of the three-scheme construction is the divorce of the customer programs from the actual database, the saved details. In physical form the details is only existent on the inner level while other forms of manifestation are determined or made respectively if needed. The DBMS has the task to understand this manifestation between each of these levels.
With knowledge about the three-scheme structure the term information self-reliance can be revealed as followed: Each advanced of the information structure is safe from changes of the next lower degree of the structure.
Therefore, the sensible structure may remain the same even though the storage space or type of some information is improved for reasons of see or reorganization.
Also the exterior structure may remain the same for most changes of the sensible structure. This is especially suitable as in this case the software does not need to be altered or fresh converted.
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