Database Management System

Transcription

1 Database Management System

2 Database: A database is a collection of data. By data, we mean known facts that can be recorded. A data Base Management System (DBMS) is a collection of Computer Programs that enables users to create and maintain a database. E.g dbase, FoxPro, MS-Access, Oracle, SQL-Server etc. Generally concepts such as entities, attributes and relationships are used to design a database.

3 Entity: An entity represents a real-world object or concept. E.g Student, Course, Books etc. In one database there may be several related entities. An entity which does not have any relationship with other entities of the database, should not be a part of the database. Attribute: An attribute represents some properties of the entities. Here values of these properties describes the entity. E.g roll_no, date_of_birth etc. are attribute of STUDENT entity.

4 Relationship: In one database there will be some relation of an entity with other entities. E.g Let there are two entities called STUDENT and TEACHER. Here a STUDENT may have one attribute called department. Again the entity TEACHER also, say, has an attribute called department. Now if student is related to the teacher depending on the value of department. Then STUDENT entity is related to TEACHER on the value of entity DEPARTMENT. Relationships of different Entities of a database are represented by a diagram known as ENTITY RELATIONSHIP diagram.

5 Advantage of using DBMS Controlling redundancy Restricting unauthorized access Quick retrieval of Information Enforcing integrity constraint User friendly interfaces for creating, manipulating and data/information retrieval.

6 Database TABLE or Database File Entities of a database are arranged as a table or file. The attributes are called FIELD of a TABLE. E.g roll_no, course_code are FIELDS of Student table Each row of a TABLE is called a RECORD. E.g: BAT10001 KAGO SAMBYO PGDTM Is one record of student table. The field whose value cannot be repeated in the table is called Primary Key field. e.g Roll_No field of student table.

7 Important tasks before creating a database using DBMS: 1. Find out the entities of the database. Against each entity, a table is to be created. 2. While creating a table, we must create the attributes or FIELDS. So, we have to find all the possible fields/attributes of the TABLE. In DBMS software, while creating the fields, we have to specify the type of data we want to keep in this FIELD. i.e we have to specify the data-types of the fields. E.g if STUDENT is a table, first we have to think of what are the different possible FIELDs. Say, we have found that the FIELDs are roll-no, name, date-of-birth, and department. Then we have to specify the data-types, e.g. roll-no as either NUMERIC if only numbers we want to keep or CHARACTER/TEXT if we want to keep alpha-numeric characters. Names are to be specified as CHARACTER/TEXT (or string). But date-of-birth is to be specified as DATE type. Data-types that can be used depends on the DBMS package. Different data types for different DBMS package is named differently.

8 3. Next, we have to specify the unique dataitems/field for the tables which is not repeated in that table. These FIELDs are called Primarykey. Primary-key are those filelds which can t be duplicated in a TABLE. E.g Roll-no, in case of Student. 4. Then we have to find out different relationships among different TABLES. Generally two tables are related to each other by one or more fields of the tables. For example, in STUDENT table ROLL-NO is primary key. Now in MARKS table we can keep the ROLL-NO and different marks. Here the tables are related by ROLL-NO field. In Marks table we don t have to keep the names.

9 MS-ACCESS 2010

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16 Primary key Length of the field.

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24 Now to define relationship between student and department

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32 Select create to create a report and then select REPORT wizard. Designing a report using wizard tool is very simple and easy.

33 First select department table and dept_code and name field and select NEXT button to select student table and few related fields like student s roll_no and name field.

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