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users might view dates in the form (day/month/year) while others prefer (year/month/day). Some views might include derived or calculated data. For example, a person’s age might be calculated from his date of birth since storing his age would require it to be updated each year. Database ApplicationsA database application is an application program or a set of related programs that is used to perform a series of activities on behalf of database users. These activities may vary application to application according to the need. These activities may include.
10Data Base Management systemsNotesAmity Directorate of Distance & Online EducationInsert: Add a new entry a new entry in the database.Update: Modify dataDelete: Delete data form the databaseRead: Read data from the database in a useful format on the screen or printer.These database applications can be of various categories from stand-alone application (only for a single user) to enterprise whose scope is the entire organization or enterprise. The size of the database may also vary ranging from megabytes to several terabytes depending upon the nature of the application. Data IndependenceThe separation of data description from the application programs that uses the data is called data independence. More simply, the ability to modify schema definitions at one level without effecting a schema definition in the next higher level is called Data Independence. Data independence can be defined at two levels: Logically and Physically. A well-designed system maintains data independence both physically as well as logically. A brief overview of both the levels are given here: a) Logical Data Independence:Logical data independence refers to the immunity of external schemas to changes in the conceptual schema. Changes to the conceptual schema (adding/removing records, columns, or relationships) should be possible without having to change existing external schemas or rewrite application programs. The database can change and grow to reflect changes in reality without requiring the user intervention or changes in the application programs or requests. For example, we can delete a field from our database if the application program is not using that field. Logical data independence is difficult to achieve than physical data independence since programs are heavily dependent on the logical structure of the database.b) Physical Data Independence:Physical data independence refers to the immunity of the conceptual schema to changes in the internal schema. Changes to the internal schema (using different storage structures or file organisations) should be possible without having to change the conceptual or external schemas.Database LanguageTo provide the various facilities to different types of users, a DBMS normally provides one or more specialized programming languages often called Database Languages. Database languages come in different forms. A language is needed to describe the database to the DBMS as well as provide facilities for changing the database and for defining and changing physical data structures. Another language is needed for manipulating