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By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database Distribution of Marks For Second Semester External Internal Sessional Evaluation Evaluation Assignment /Project Quizzes Class Attendance Mid-Term Test Total Sessional Terminal Exam Final Evaluation 10 10 5 25 50 50 100 Remember: 1 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database Course Contents Chapter No Chapter Name 1. Database Foundation OR An Overview of Database Management System (DBMS) 2. Semantic Modeling OR Entity Relationship Model (ERD) 3. An introduction to Relational Database 4. Normalization 5. Relational Algebra 6. An Introduction to Structured Query Language (SQL) Page No 2 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database DATABASE-1 Chapter No: 03 Chapter No: 03 COURSE TITLE: COURSE INSTRUCTOR: ILTAF MEHDI 3 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database DATA MODEL Def:“A data model is a representation of data about entities, events, activities and their relationship”. A data model represents an organization itself. The purpose of data model two-fold: First “to represent data” and second “to be understandable”. If a data model accurately and completely represent required data and is understandable then it can be used in some application. 4 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF DATA MODEL There are basically three types of data model: 1) Hierarchical Data Model 2) Network Data model 3) Relational Data model 5 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF DATA MODEL Relational Data Model: It also called Relational Database Model. The Relational Data Model is the most recent and best of the three database models. It was developed by C.F Codd in 1970. This model represents database as a set of normalized relations. “In Relational Model data are represented in the form of tables with rows and columns”. 1) 6 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database RELATIONAL DATABASE MODEL DEPARTMENT EMPLOYEE Deptt-No Deptt-Name DepttLocation Emp-No EmpName EmpPhone # Deptt-No D100 IT West E10 Mehdi 336 D100 D101 Management East E11 Danish 448 D101 D102 English South E12 Nasir 500 D102 Relational Database Model Notice that there is no physical data structure representing relationship between two tables (relations). Instead relationships are represented logically by the values that are stored within table’s columns. For example: In above figure, the Department-Number (Deptt-No) for each Employee is stored in Employee table. 7 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database PROPERTIES OF RELATION (TABLE) The above tables have the following properties: 1. Each column contained values about some attribute. 2. Each column has distinct name. 3. Each row of a table must be unique, means, that no two rows have the identical data. 4. Each row in the relation is called TUPLE. 5. Each column in the relation is called DOMAIN. 8 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database PROPERTIES OF RELATION 6. Record: “The combination of more than one fields about a single entity is called record of that entity”. For example: The record of STUDENT may have fields Roll-No, Name, Father Name, Gender, Address, Program and Marks. Then this combination of fields is called the record of a particular STUDENT. STUDENT FILE Roll-No Name F-Name Gender Address Program Marks 100 Abdullah Zain Male Kabul BCS 40 1st RECORD 101 Spogmay Iqbal Female Kabul BCS 47 2nd RECORD FIELDS 9 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database PROPERTIES OF RELATION 7. File or Data File: “The collection of more than one related records is called a file or data file”. All the records of the should be of the same type. In the above File, two logical records about STUDENT are shown. 8. Degree of file: “The total number of the columns in a file is called Degree of a file”. 9. Cardinality: The total number of rows or records in a file is called cardinality. 10 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database Properties of Relation STUDENT Relation Roll-No Name 100 Abdullah F-Name Gender Address Zain Male Kabul Program Marks BCS 40 Two Records 101 Spogmay Iqbal Female Kabul BCS 47 Cardinality: 02 SEVEN FIELDS Degree of File: 07 11 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database ADVANTAGES OF RELATIONAL DATA MODEL The Relational Data Model has several advantages but some of them are given below: 1) Implementation Independence: R.D.M logically represents all relationship implicitly and completely. 2) Terminology: The R.D.M has developed with its own set of terminology. 3) Logical Key Pointer: The R.D.M uses primary and secondary keys to represent relationship between two relations. 12 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database KEYS Def: “a key is a data item which is used to identify a record or relation”. OR An attribute through which we can access an entity within entity class”. 13 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY There are different types of keys which are given below: 1. Super Key 2. Candidate Key 3. Primary Key 4. Atomic Key 5. Concatenated Key 6. Compound Key 7. Secondary Key 8. Foreign Key 14 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY Super Key: “An attribute or combination of attributes that can uniquely identify an entity is called super key”. For Example: consider the STUDENT relation; STUDENT (st-no, st-name, st-age, st-gender etc) A super key may contain some extra attributes that are not necessary to uniquely identify an entity. i.e. { st-no, st-name, st-age } In-fact a super key can be: { Primary-key + Non-key attribute } 1) 15 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY Candidate Key: “An attribute or combination of attributes that uniquely identifies each instances of an entity is called Candidate Key”. For Example: consider the EMPLOYEE relation; EMPLOYEE (NIC-No, Name, Address etc) Here NIC-No and Name is a super key that contain extra attributes that is not necessary for unique identification. So it is not a candidate key. But NIC-No is a Candidate Key. An entity may be uniquely identified by more than one candidate keys. 2) 16 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY 3) Primary Key: Def: “A primary key is a key that have been selected as an identifier for an entity type”. It is also called identifier. For example: Consider the EMPLOYEE relation; EMPLOYEE (Emp-No, Emp-Name, Emp-Address) If we select Emp-No as an identifier then it is Primary Key. 17 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY 4) Atomic Key: Def: “A Primary Key is called atomic key or simple key when it consists of a single attribute to identify a record or relation”. For Example: Consider the STUDENT relation; STUDENT (St-ID, St-Name, St-F/Name,St-Address) St-ID is atomic key for the STUDENT relation 18 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY 5) Concatenated Key: Def: “The combination of two or more keys to uniquely identify a record is called Concatenated Key”. For Example: Consider the STUDENT relation; STUDENT (class-no, name, address, class) “We have student file of Computer Science Department that contain information about Previous and Final students”. In this case class-no can’t uniquely identify a student because there may be duplication of students for class i.e. Previous and Final. So both class-no and class can be used as Primary Key in this case. Such a key is called Concatenated Key. 19 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY 6) Compound Key: Def: “A Compound Key is a Primary Key that consists of more than one attribute and every attribute in the key is Primary key in some other relation”. For Example: Consider the relation; ORDER-LINE (order-no, product-no, quantity, date) So the primary key consists of order-no and product-no. But order-no is primary key in ORDER relation and product-no is primary key in PRODUCT relation. So it is a Compound Key. 20 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY 7) Secondary Key: “A secondary key is a data item that does not uniquely identify a record but identifies a number of records in a set that share some common property ”. For Example: Name, Address, Age etc are the examples of Secondary Key. Now consider the Query: Select * from student where Age=‘20’ ; So based on secondary key “Age” this query will select all students whose age is 20. 21 By ILTAF MEHDI (MCS, MCSE, CCNA) An introduction to Relational Database TYPES OF KEY 8) Foreign Key: Def: “An attribute that appear as non-key in one relation but primary key in another relation is called Foreign Key”. For Example: Consider the relations; DEPARTMENT (Deptt-No, Deptt-Name, Location) TEACHER (T-No, T-Name, Deptt-No ) Here Deptt-No is a foreign key because it act as primary key in DEPARTMENT and as non-key attribute in TEACHER relation. 22