Database System Components and Core Concepts
Components of Database Systems
The components that constitute a database system include:
- The Database
- The Database Management System (DBMS) or engine (e.g., Oracle, Sybase, SQL Server)
- Application Programs
- A set of qualifiers (DBA, application programmers, etc.)
- A set of users (system operators, management)
- Machines
Database Management System (DBMS)
DBMS stands for Database Management System. This corresponds to the software that manages all access to the database. Every request for access by a user is processed and inspected by the DBMS, which then generates a coherent response to the needs of the query.
User Interface
The user interface is the access boundary available to a common user to the base. Everything below this boundary is transparent to the user.
Database Administrator (DBA)
The Database Administrator (DBA) is the person or persons responsible for overall system control. Their responsibilities and functions include system management and security.
DBMS Languages
The various functions performed by a DBMS necessitate different languages and procedures for communication with the database.
Based on the type of function, we define definition languages and manipulation languages.
Based on the type of computer user, we have languages for computer specialists and languages for end users. The latter can be formalized applications (such as personnel management systems) or used for non-formalized decision-making processes.
Fundamental Concepts
Entity
An entity is a concrete or abstract object of interest to the system, containing information to be represented in a database system. Most entities or objects model real-world events, such as customers, products, or orders.
Attribute
An attribute is a basic and indivisible unit of information about an entity or a relationship, serving to identify and describe them. For example, if modeling a helpdesk call as an entity, you would likely want to know who made the call, when it occurred, and whether the problem was resolved. The determination of attributes to include in the model is a matter of semantics (meaning); decisions must be based on the meaning of the data and how they are used.
Domain
A domain is the set of values that each attribute can take. A domain is often confused with a data type. Consider an attribute like a person’s blood group: the information type must be a string, but it can only take values from the set {A+, A-, B+, B-, AB+, AB-, O+, O-}; this set constitutes the attribute’s domain.
Table
A table is the organization of data into rows and columns. Each row is called a tuple (or record), and each column within a tuple represents the value of an attribute for that tuple.
Basic Characteristics of a Database
The goal of reducing data redundancy identifies two key features inherent in any Database system:
Integrated
Integrated means that a database can be viewed as a unification of several independent data files, which partially or completely eliminates redundancy among them. For example, a database might contain employee records (name, address, department, pay, etc.) and course registration records. If course registration needs the employee’s department, this data should not be duplicated (redundant) in the registration records; it can always be retrieved using the employment records.
Shared
Shared means that individual parts of the database can be accessed by several different users for different purposes. This sharing is possible because the database is integrated. In the previous example, employment data is shared by users in the personnel department and the training department. A consequence of integration is that any user accesses only a subset of the full database, and these subsets may be processed differently by different users. In other words, different users perceive the database in very different ways.