DBMS
A software system that enables users to define, create, maintain and control access to the database.
Relational Database Model (RDBMS)
In
... [Show More] the relational model, all data is logically structured within relations (tables).
Each relation has a name and is made up of named attributes (columns) of data.
Each tuple (row) contains one value per attribute.
DBMS Functions
It allows users to define the database, usually through a Data Definition Language( DDL). The DDL allows users to specify the data types and structures and the constraints on the data to be stored in the database.
It allows users to insert, update, delete, and retrieve data from the database, usually through a Data Manipulation Language (DML).
It provides controlled access to the database. For example, it may provide:
- a security system, which prevents unauthorized users accessing the database;
- an integrity system, which maintains the consistency of stored data;
- a concurrency control system, which allows shared access of the database;
- It provides a range of management functions and tools that should be appreciated on focusing on the creation, manipulation and interrogation of a databse.
Database Definition
- Defining a database involves specifying the data types, structures, and constraints of the data to be stored in the database.
- The database definition or descriptive information is also stored by the DBMS in the form of a database catalog or dictionary; it is called meta-data.
Constructing the Database
The process of storing the data on some storage medium that is controlled by the DBMS.
Manipulating a database
Functions such as querying the database to retrieve specific data, updating the database to reflect changes in the miniworld, and generating reports from the data
Accessing a database through an application program
A program that accesses the database by sending queries or requests for data to the DBMS. A query typically causes some data to be retrieved; a transaction may cause some data to be read and some data to be written into the database.
Sharing a database
Allows multiple users and programs to access the database simultaneously.
Protecting a database
The database and maintaining it over a long period of time.
Protection includes system protection against hardware or software malfunction (or crashes) and security protection against unauthorized or malicious access.
How a DBMS can be used to promote data security
- Data Validation
- Access rights
- Data Locking
Schema
The description of a database, which is specified during the database design.
Internal Schema
The internal level has an internal schema,which describes the physical storage
structure of the database. The internal schema uses a physical data model
and describes the complete details of data storage and access paths for the
database.
Conceptual Schema
Describes the structure of the whole database for a community of users. The conceptual schema hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints.
External Schemas or User Views
Each external schema describes the part of the database that a particular user group is interested in and hides the rest of the database from that user group. As in the previous level, each external schema is typically implemented using a representational data model, possibly based on an external schema design in a high-level data model. [Show Less]