DBMS Structure
Applications: - It can be considered as a user
friendly web page where the user enters the requests. Here he simply enters the
details that he needs and presses buttons to get the data.
End User: - They are the real users of the database.
They can be developers, designers, administrator or the actual users of the
database.
DDL: - Data Definition Language (DDL) is a query
fired to create database, schema, tables, mappings etc in the database. These
are the commands used to create the objects like tables, indexes in the
database for the first time. In other words, they create structure of the
database.
DDL Compiler: -
DML Compiler:
- When the user inserts, deletes, updates or retrieves the record from the
database,
Query Optimizer: -The query optimizer decides the
best way to execute the user request which is received from the DML compiler
Stored Data Manager: -It converts the requests
received from query optimizer to machine understandable form.
Data Files: - It has the real data stored in it. It
can be stored as magnetic tapes, magnetic disks or optical disks.
Compiled DML: - Some of the processed DML statements
(insert, update, delete) are stored in it so that if there is similar requests,
it will be re-used.
Data Dictionary: - It contains all the information
about the database. As the name suggests, it is the dictionary of all the data
items. It contains description of all the tables, view, materialized views,
constraints, indexes, triggers etc.
Generalization
Generalization is like a bottom-up approach in which two or more entities of lower level combine to form a higher level entity if they have some attributes in common.
In generalization, an entity of a higher level can also combine with the entities of the lower level to form a further higher level entity.
Generalization is more like subclass and superclass system, but the only difference is the approach. Generalization uses the bottom-up approach.
In generalization, entities are combined to form a more generalized entity, i.e., subclasses are combined to make a superclass.For example, Faculty and Student entities can be generalized and create a higher level entity Person.
Specialization
Specialization is a top-down approach, and it is opposite to Generalization. In specialization, one higher level entity can be broken down into two lower level entities.Specialization is used to identify the subset of an entity set that shares some distinguishing characteristics.
Normally, the superclass is defined first, the subclass and its related attributes are defined next, and relationship set are then added.
For example: In an Employee management system, EMPLOYEE entity can be specialized as TESTER or DEVELOPER based on what role they play in the company.
Aggregation
In aggregation, the relation between two entities is treated as a single entity. In aggregation, relationship with its corresponding entities is aggregated into a higher level entity.
For example: Center entity offers the Course entity act as a single entity in the relationship which is in a relationship with another entity visitor. In the real world, if a visitor visits a coaching center then he will never enquiry about the Course only or just about the Center instead he will ask the enquiry about both.
Generalization
Generalization is like a bottom-up approach in which two or more entities of lower level combine to form a higher level entity if they have some attributes in common.
In generalization, an entity of a higher level can also combine with the entities of the lower level to form a further higher level entity.
Generalization is more like subclass and superclass system, but the only difference is the approach. Generalization uses the bottom-up approach.
In generalization, entities are combined to form a more generalized entity, i.e., subclasses are combined to make a superclass.For example, Faculty and Student entities can be generalized and create a higher level entity Person.
Specialization
Specialization is a top-down approach, and it is opposite to Generalization. In specialization, one higher level entity can be broken down into two lower level entities.Specialization is used to identify the subset of an entity set that shares some distinguishing characteristics.
Normally, the superclass is defined first, the subclass and its related attributes are defined next, and relationship set are then added.
For example: In an Employee management system, EMPLOYEE entity can be specialized as TESTER or DEVELOPER based on what role they play in the company.
In aggregation, the relation between two entities is treated as a single entity. In aggregation, relationship with its corresponding entities is aggregated into a higher level entity.
For example: Center entity offers the Course entity act as a single entity in the relationship which is in a relationship with another entity visitor. In the real world, if a visitor visits a coaching center then he will never enquiry about the Course only or just about the Center instead he will ask the enquiry about both.
