Characteristics of the Database Approach

Characteristics of the Database Approach


The main characteristics of the database approach are the following:

  1. Self-describing nature of a database system
  2. Insulation between programs and data, and data abstraction
  3. Support of multiple views of the data
  4. Sharing of data and multiuser transaction processing

Self-Describing Nature of a Database System

A fundamental characteristic of the database approach is that the database system contains not only the database itself but also a complete definition or description of the database structure and constraints.

This meta-data (i.e., data about data) is stored in the so-called system catalog, which contains a description of the structure of each file, the type and storage format of each field, and the various constraints on the data (i.e., conditions that the data must satisfy).

The system catalog is used not only by users but also by the DBMS software, which certainly needs to “know” how the data is structured/organized in order to interpret it in a manner consistent with that structure.

Insulation between programs and data, and data abstraction

Program-Data Independence:

the DBMS provides a conceptual or logical view of the data to application programs, so that the underlying implementation may be changed without the programs being modified. (This is referred to as program-data independence.)

Program-operation independence:

In object-oriented and object-relational systems, users can define operations on data as part of the database definitions. An operation (also called a function or method) is specified in two parts. The interface (or signature) of an operation includes the operation name and the data types of its arguments (or parameters). The implementation (or method) of the operation is specified separately and can be changed without affecting the interface. User application programs can operate on the data by invoking these operationsthrough their names and arguments, regardless of how the operations are implemented. This may be termed program-operation independence.

Data abstraction :
The characteristic that allows program-data independence and program- operation independence is called data abstraction.

Support of Multiple Views of the Data

A database typically has many users, each of whom may require a different perspective or view of the database. A view may be a subset of the database or it may contain virtual data that is derived from the database files but is not explicitly stored. A multiuser DBMS whose users have a variety of distinct applications must provide facilities for defining multiple views. For example, one user of the database of Figure 1.2 may be interested only in accessing and printing the transcript of eachstudent; the view for this user is shown in Figure 1.2(b)

Fig1.2(b): view derived from the university database

Sharing of Data and Multiuser Transaction Processing

A multiuser DBMS lets many people use the database at once. It controls who can update data to avoid conflicts, like when multiple agents try to assign seats on a plane. This is important for applications like airline reservations. The DBMS ensures that transactions, which are sets of actions on the database, follow certain rules. One rule is isolation, which keeps transactions separate even if many are happening at once. Another rule is atomicity, which ensures that either all actions in a transaction happen or none do.

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