Databases

Any collection of data, or information, that is specially organized for rapid search and retrieval by a computer. Databases are structured to facilitate the storage, retrieval, modification, and deletion of data in conjunction with various data-processing operations. A database management system (DBMS) extracts information from the database in response to queries.

Serial file

A file where the records are held and accessed in sequence but where they are not sorted on any key field and the order is random.

Sequential file

A sequential file is one which must be read in serial order; processors cannot skip around or begin to read or write to a sequential file in any other direction but forward.

External view:

 This is the highest level view, as seen by the user. This level of view describes only one part of entire database that you specifically want to see.

Conceptual view:

 This level describes what data is actually stored in the database. This level contains information about entire database in text form.

Physical level:

This is the lowest level of view at which one describes how the data is physically stored. For example this could be in hex or binary.

 

Flat file

A flat file database is a database that stores data in a plain text file. Each line of the text file holds one record, with fields separated by commas or tabs. It uses a simple structure, usually a table.

 

Hierarchical file

A hierarchical file system is how drives, folders, and files are displayed on an operating system. In a hierarchical file system, the drives, folders, and files are displayed in groups, which allows the user to see only the files they're interested in seeing. For example, in the picture the Windows directory (Windows\) folder hierarchy

that contains the System32, Tasks, and Web folders. Each of these folders could have hundreds of their own files, but unless they are opened the files are not displayed.