Definition and examples of DBMS:
Database Management System is a software that allows you to describe, modify, query and administer the data in a database.
A DBMS consists of two main components:
- The engine that performs the main functions of a DBMS.
- The interface (between Database users and the engine) allows easy access to data.
There are many relational database systems such as MySQL, MS Access, Oracle, Sybase, Informix, Postgres, and SQL Server
The DBMS provides a set of features :
Definition of data:
The DBMS offers a Data Description Language (DDL), which describes:
- The list of objects (entities)
- The list of attributes of each object
- List of links between objects (relationships)
- The list of constraints (a constraint is a mandatory rule that can be applied to an object, an attribute or a relation)
- List of objects: customer, rental, cars
- List of attributes: Id, first name, last name
- Constraint: a customer cannot rent more than one car at a time.
The DBMS offers a Data Manipulation Language (DML), which allows, using queries, to perform:
- Data searches
- Data creations
- Data modifications
- Data deletions.
- Insertion / addition of new cars.
- Modification of a customer's address
- Deleting a car
- Find loyal customers (who often rent cars)
Integrity helps to ensure the consistency and reliability of data by respecting certain rules called integrity constraints.
Examples: in the school database, the note attribute must contain values between 0 and 20.
Concurrent access management
The DBMS offers mechanisms for managing conflicts (problems) with simultaneous access. Among these mechanisms: allow multiple access when viewing data or lock the data in the event of modification for certain users.
Examples: prohibit modification of data for a group of users and allow it for others
The DBMS ensures data confidentiality through passwords and access privileges.
Example: only the principal can modify the assignment of a student.
The DBMS offers mechanisms to quickly restore the Database to an operational state in the event of a hardware or software incident. They are based on (historical) logging of the Database and their automatic replay.
Examples: Backing up the Database once a week; Database restoration in the event of a breakdown.
Notes : A portable DBMS is a DBMS independent of the operating system, it is operational whatever the system: it does not use the functionalities of the S.E.
The database development cycle
There are 4 levels of data representation (conceptual, logical, external and internal):
- The conceptual level is independent of any technology (independent of the DBMS); it concerns the definition of data
- The logical level which structures the data according to the relational model
- The external level concerns the manipulation of the database by user applications
- The internal (physical) level contains the list of constraints related to the hardware and software used. (it depends on the DBMS)
To complete the establishment of the database, one must write the list of programs, test, install, operate and maintain a test base.
Stakeholders in the database domain
Stakeholders can be classified according to their function, their type of activity and the degree of specialization required to ensure this activity.
- Occasional users use the DML
- Naive users access the database by "press-button"
- Specialized users master the use of different DBMS tools
Designers and developers
- Designers define the structure of databases and manipulate software design
- Application developers build programs and master DML
Database and systems administrators
- They are responsible for one or more databases.
- They ensure the role of issuing access authorizations to the base and coordinating activities
- They are responsible for DBMS performance and operational safety issues
Database management and development software developers
- Developers of tools facilitating the design, implementation and use of databases
- DBMS designers have mastered DBMS implementation techniques, compilation, operating system, networks, etc.