what is database abstraction, what are three levels of data abstraction?
DATABASE ABSTRACTION
as we know that a collection of interrelated files and a set of programs that allow users to access and modify these files is known as a database management system. a major purpose of a database system is to provide the users only that much information that is required by them. this means that the system does not disclose all the details of data, rather it hides certain details of how the data is stored and maintained. A good database system ensures easy, smooth and efficient data structures in such a way so that every type of database users; end user, application system analyst , is able to access its desired information efficiently. (An end user is a person who is not a computer trained person but uses the database to retrieve some information.) for example, in a bank database,a customer, who wants to know how balance remains in his account, is an end user. An application system analyst is the one who is concerned about all of the database of logical level i.e., what all data constitute the database, what are the relationships between the data entities etc. without considering the physical implementation details. the third type of user, the physical storage system analyst is concerned with the physical implementation details of the database i.e., how would the database be stored on which storage device? what will be the starting address of the database? what will be the storage technique? etc.
since the requirements of different users differ from one another, the complexity of the database is hidden from them, if needed, through several levels of abstraction in order to simplify their interaction with the system. the various levels of database implementation are being discussed in the following section.
various levels of database abstraction :
a database is implemented through three general levels, internal, conceptual and external so as cater to the needs of its users.
1. internal level(physical level) : The lowest level of abstraction,the internal level is the one closest to physical storage. this level is also sometimes termed as physical level. it describes how the data are actually stored on the storage medium. At this level, complex low-level data structures are described in details.
2. conceptual level : This level of abstraction describes what data are actually stored in the database. it also describes the relationships existing among data. At this level, the database is described logically in terms of simple data structures. the users of this level are not concerned with how logical data structures will be implemented at the physical level. Rather, they just are concerned about what information is to be kept in the database.
3.external level (view level) : this is the level closest to the users and is concerned with the way in which the data are viewed by individual user. Most of the users of the database are not concerned with all the information contained in the database. instead, they need only the part of the database relevant to them. For example, even though the bank database stores a lot many information, an account holder (a user) is interested only in his account details and not with the rest of the information stored in the database. To simply such users, interaction with the system, this level of abstraction is defined. the system, thus provides many views for the same database.
as we know that a collection of interrelated files and a set of programs that allow users to access and modify these files is known as a database management system. a major purpose of a database system is to provide the users only that much information that is required by them. this means that the system does not disclose all the details of data, rather it hides certain details of how the data is stored and maintained. A good database system ensures easy, smooth and efficient data structures in such a way so that every type of database users; end user, application system analyst , is able to access its desired information efficiently. (An end user is a person who is not a computer trained person but uses the database to retrieve some information.) for example, in a bank database,a customer, who wants to know how balance remains in his account, is an end user. An application system analyst is the one who is concerned about all of the database of logical level i.e., what all data constitute the database, what are the relationships between the data entities etc. without considering the physical implementation details. the third type of user, the physical storage system analyst is concerned with the physical implementation details of the database i.e., how would the database be stored on which storage device? what will be the starting address of the database? what will be the storage technique? etc.
since the requirements of different users differ from one another, the complexity of the database is hidden from them, if needed, through several levels of abstraction in order to simplify their interaction with the system. the various levels of database implementation are being discussed in the following section.
various levels of database abstraction :
a database is implemented through three general levels, internal, conceptual and external so as cater to the needs of its users.
1. internal level(physical level) : The lowest level of abstraction,the internal level is the one closest to physical storage. this level is also sometimes termed as physical level. it describes how the data are actually stored on the storage medium. At this level, complex low-level data structures are described in details.
2. conceptual level : This level of abstraction describes what data are actually stored in the database. it also describes the relationships existing among data. At this level, the database is described logically in terms of simple data structures. the users of this level are not concerned with how logical data structures will be implemented at the physical level. Rather, they just are concerned about what information is to be kept in the database.
3.external level (view level) : this is the level closest to the users and is concerned with the way in which the data are viewed by individual user. Most of the users of the database are not concerned with all the information contained in the database. instead, they need only the part of the database relevant to them. For example, even though the bank database stores a lot many information, an account holder (a user) is interested only in his account details and not with the rest of the information stored in the database. To simply such users, interaction with the system, this level of abstraction is defined. the system, thus provides many views for the same database.
Comments
Post a Comment