Different Levels in Database system

[B-JOB Guru]

I know that the making a database in million dollar question but knowing that how database works and relations made with an entities of the database are more important to know. I have just started studying about the databases and it is just a start. I want to ask you guys about the database levels. I just didn't understood that how database has levels and what are they?

[Shreevats]

A database (DB, Eng. Data Base) is a systematic collection of data. To use and manage the data stored in the database the user needs a database management system (DBMS, Eng. Data Base Management System). The combination of DBMS and DB is the database system (DBS, Eng. Data Base System), but is often mistakenly referred to as a database. The DBMS consists of a variety of tools and generators ("producers ``). On the one hand, it provides the developer with the tools available with which he can describe the data model and set up. On the other hand, it offers the functions with which the individual user to enter data, change, query, and can spend. All functions of the DBMS are, what `` and no more, as `` specified and is hot: The developer tells the program logic with the data and the user formulates his query. How to store the data and manage, is for the DBMS. This is therefore responsible for the technical implementation of the requirements of the developer and the user.

[Vandam]

A database system (DBS, Eng. Data Base System, = DB + DBMS) consists of four levels: First level is Operating System / Hardware : This is the lowest level at which any computer based application. In addition to the DBS also build any other program at this level. One can divide this level but even more: First, there is the absolutely lowest hardware level, the possibilities of the operating system (OS) manages. The operating system on the other offers programs the hardware capabilities, without that, the programs address the hardware directly.

[Ronchi]

Next two levels are Internal level & Conceptual level.

Internal level : On the internal level is the physical storage of data. The memory logic that is used here, depends on the DBMS and the developer can be quite matter since they access only on the conceptual level to the DB. The user does not need to worry about the internal nor the conceptual level in that it first over the top, namely the external level, the DB access.

Conceptual level : On the third, the conceptual level, the data model is described. In a data model is defined as the consistent data image of a certain section of the real environment. In the data model the structures of the data and their relationship to each other established. After the way the relationships are governed by the data model, you can distinguish between hierarchical, networked, object-oriented, object-relational and relational data models.

[justinepeter]

The three-schema architecture is a convenient tool for the user to visualize the schema levels in a database system. Most of the DBMS’s do not separate the three levels completely, but support three-schema (Level) architecture. These are-
1. Internal level,
2. Conceptual level,
3. External level.
The external or view level includes a number of user views. Each external schema describes the part of the database that a particular user group is interested in and hides the rest of the database from other user groups. Implementation data model is used at this level.

[Villiers]

Last level is an External Level : At the top level is the user that the DBS with a data query language (DQL, Eng. Data Query Language), a data manipulation language (DML, Eng. Data Manipulation Language) or a custom application, which in our example, the Web page is accessed.

The relational data model, the data is arranged in two-dimensional tables. Each table has a unique relation names. All rows from the table (without the column header row) are as a relation, every line of it as a tuple or record, the column headers as attributes and attribute names or attribute names all together are called relation schema. It is generally displayed in each line entity.