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Database schema

A Database Schema is an outline or model focusing on the way that database information is organized. Databases are stored and accessed through machines and computers. These databases are organized and formatted using tables, which consists of columns and rows, much like an Excel spreadsheet. These columns and row are fields that contain data.  Relating data are linked from a field to table and from table to table, based on their designated relationships to each other. The schema of the database is the way that the relationship between the table and the fields in that table would be described for that particular database.

There are 4 Levels of Database Schema:

1.      Conceptual Schema

2.      Logical Schema

3.      Physical Schema

4.      Schema Object

Conceptual Schema

Conceptual Schema, also known as a conceptual data model, logically shows concepts and their relationships to one another. A data structure diagram (DSD) can be used to help better recognize, through pictorials, the relationships of concepts of a conceptual schema. Conceptual schema focuses more on the relationships of the data in the database rather than on the design of the database itself. In information systems, conceptual schema mostly focuses on the details of applications and their functions.

Logical Schema
Logical Schema is a model which describes how data is presented. Logical Schema describes relationships in terms of the data management technology used, unlike conceptual or physical    schema, which do not refer to the data in technological terms. Logical schema are described as being in “
terms of either (for example, in 2007) relational tables and columns, object-oriented classes, or XML tags.”

Physical Schema
Physical Schema describes how data is physically stored.

Schema Object

A Schema Object is an object in which data is stored. Schema objects take the form of:

  •          tables
  •          views
  •          sequences
  •          synonyms
  •          indexes
  •          clusters
  •          database links
  •          snapshots
  •          procedures
  •          functions
  •          packages



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