Short for relational database management system and pronounced as separate letters, a type of database management system (DBMS) that stores data in the form of related tables. Relational databases are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways.
An important feature of relational systems is that a single database can be spread across several tables. This differs from flat-file databases, in which each database is self-contained in a single table.
Almost all full-scale database systems are RDBMS's. Small database systems, however, use other designs that provide less flexibility in posing queries.
Logical view and physical view of DBMS
A database management system provides the ability for many different users to share data and process resources. But as there can be many different users, there are many different database needs. The question now is: How can a single, unified database meet the differing requirement of so many users?
A DBMS minimizes these problems by providing two views of the database data: a physical view and a logical view. The physical view deals with the actual, physical arrangement and location of data in the direct access storage devices(DASDs). Database specialists use the physical view to make efficient use of storage and processing resources. Users, however, may wish to see data differently from how they are stored, and they do not want to know all the technical details of physical storage. After all, a business user is primarily interested in using the information, not in how it is stored. The logical view/user’s view, of a database program represents data in a format that is meaningful to a user and to the software programs that process those data. That is, the logical view tells the user, in user terms, what is in the database. One strength of a DBMS is that while there is only one physical view of the data, there can be an endless number of different logical views. This feature allows users to see database information in a more business-related way rather than from a technical, processing viewpoint. Thus the logical view refers to the way user views data, and the physical view to the way the data are physically stored and processed.
A DBMS minimizes these problems by providing two views of the database data: a physical view and a logical view. The physical view deals with the actual, physical arrangement and location of data in the direct access storage devices(DASDs). Database specialists use the physical view to make efficient use of storage and processing resources. Users, however, may wish to see data differently from how they are stored, and they do not want to know all the technical details of physical storage. After all, a business user is primarily interested in using the information, not in how it is stored. The logical view/user’s view, of a database program represents data in a format that is meaningful to a user and to the software programs that process those data. That is, the logical view tells the user, in user terms, what is in the database. One strength of a DBMS is that while there is only one physical view of the data, there can be an endless number of different logical views. This feature allows users to see database information in a more business-related way rather than from a technical, processing viewpoint. Thus the logical view refers to the way user views data, and the physical view to the way the data are physically stored and processed.
3D Operations in DBMS
Although it is possible to maintain objects with 3D coordinates, the functions implemented still omit the z-value.Some exceptions are PostGIS and MapInfo Spatialware Datablade (based on Informix) that do support geometry calculation such as 3D length and 3D perimeter in 3D. Existing spatial functions are developed only on the basis of a geometry model (with exception Oracle Spatial 10g), but they still can perform topological operations such as overlap, touch, etc.
The problem with 3D operations is twofold: first, the existing operations have to extend to consider the z-coordinate, and second, new operations have to be developed on the basis of topological models.
Furthermore, since the two models (geometry and topology) are to be maintained in DBMS, operations for conversion between the two has to be ensured, i.e.operators for building topology and operators for realization of geometry.
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