Topic 05 & 06 : The Relational Model

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Information about Topic 05 & 06 : The Relational Model

Published on January 7, 2014

Author: PradipKharbuja


Topic 5 & 6 The Relational Model Er. Pradip Kharbuja

Terminology 1. Relation A relation is a table with columns and rows. 2. Attribute The columns in a relation are known as attributes. 3. Domain A domain or attribute domain is the set of allowable values for one or more attributes. 4. Tuple A tuple is a row of a relation. They are also called the records.

Terminology 5. Degree The degree of a relation is the number of attributes it has. Example, the department table has 3 attributes. So, is has degree three. 6. Cardinality The cardinality of a relation is the number of tuples it contains. 7. Relational Database A collection of normalized relations with distinct or unique relation names. It consists of relations that are appropriately structured having no repeating groups. This is known as Normalization.

Student Table 4 Tuples Student ID First Name Last Name Course Code S334 Dave Watson COMP S765 Jagpal Jutley COMP S783 Cynthia Kodogo HIST S111 Walace Antigone LIT 4 Degree Cardinality 4 Attributes

Alternative Terminology Formal Term Alternative 1 Alternative 2 Relation Table File Tuple Row Record Attribute Column Field

Background to Relational Model  Proposed by E.F. Codd in 1970 in his seminal paper “A relational model of data for large shared data banks”  In the relational model of a database, all data is represented in terms of tuples, grouped into relations.  A database organized in terms of the relational model is a relational database.  The purpose of the relational model is to provide a declarative method for specifying data and queries : users directly state what information they want from database and let the database management system software take care of describing data structures for storing the data.

RDBMS  A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E.F. Codd.  Dominates the market in databases  Many popular databases currently in use are based on the relational database model. e.g. Oracle, MySQL, Microsoft SQL Server, etc.  Second generation of DBMSs  The first generation of database technology started in the 60's and continued into the 70's.

Do not confuse relations with relationships in ER models

Objectives of Relational Model 1. To allow a high degree of data independence. 2. To reduce the redundancy of relations. Relations should be normalized. 3. To enable the expansion of set-orientated data manipulation languages.

Data Independence  Application programs must not be affected by modifications to the internal data representation, particularly by changes to file structure, record orderings, access paths, or using different storage devices.

Normalized Relation  Codd's paper introduced the concept of normalized relation, i.e. relations having no repeating groups.  The process of normalization is about structuring the data so as to minimize redundancy and duplication.  Ideally, an item of data should be stored only in one place.  In practice, there is some duplication due to the use of foreign keys.

Set-Orientated Data Manipulation Languages  SQL is based on the set theory from Mathematics.  The relational model has used languages like relational algebra and relational calculus from set theory from Mathematics to express data manipulation.  e.g. UNION, Cartesian Product, Intersection, etc.

Presentation 1. System R 2. INGRES 3. Peterlee Relational Test Vehicle(PRTV)

History – Practical Developments - 1  System R. Developed by IBM's San Jose laboratory in late 1970s and involved some of the key people in the early development of databases, such as Codd and Boyce.  System R was the first implementation of SQL.  Development of commercial database systems DB2; SQL/DS; Oracle  Other aspects are transaction management, concurrency control, recovery techniques, query optimization, data security, data integrity, user interfaces.  It was also the first system to demonstrate that a relational database management system could provide good transaction processing performance.

History – Practical Developments - 2  INGRES. Developed by University of California in late 1970s  INGRES stands for Interactive Graphics Retrieval System.  It was used to investigate the concepts of the relational model.  It is a commercially supported, open-source SQL relational database management system.  Ingres spawned a number of commercial database applications, including Sybase, Microsoft SQL Server.  Postgres (Post Ingres), a project which started in the mid-1980s, later evolved into PostgreSQL.

History - Practical Developments - 3  Peterlee Relational Test Vehicle(PRTV). Developed at IBM UK in 1976  It was the first relational database to be able to handle large volumes of data in term of both rows and columns.  It was a relational query system with powerful query facilities, but very limited update facility and no simultaneous multiuser facility.

Properties of a Relation  It has a name which is unique within the relational schema. e.g. department_name column should not contain values other than department's name.  Each cell of a relation contains exactly one value.  Each attribute has a name.  Each tuple is unique.  The order of attributes is insignificant.  The order of tuples is insignificant.

Activity - Is This a Relation? Student Name Modules Guy Smith Med1 Medieval History 1 Course History Med2 Medieval History 2 Sarah Anusiem TCE Twentieth Century OS Operating Systems 12 New Street, Lagos NET Networks Computing

Activity - Is This a Relation?  It has a name which is unique within the relational schema - No  Each cell of a relation contains exactly one value - No  Each attribute has a name – YES  Each tuple is unique - YES  The order of attributes is insignificant – YES  The order of tuples is insignificant - YES

Now a Relation Student Name Address Modules Course Guy Smith Med1 Medieval History 1 History Guy Smith Med2 Medieval History 2 History Guy Smith TCE Twentieth Century Sarah Anusiem 12 New Street, OS Operating Systems Lagos Sarah Anusiem 12 New Street, NET Networks Lagos History Computing Computing

Class Record Class Code Instrument Taught Teachers 2 6 7 9 1 Saxophone Trumpet Marcus Smith Ajay Singh No of Instruments Rented 10 20 Guitar Guitar Sonny Muller Farhad Khan Farhad Khan 10 23 Drums Tommy Jones Tommy Jones 5

Class Record – A Relation Class Code Instrument Taught Teachers No of Instruments Rented 2 Saxophone Marcus Smith 10 6 Trumpet Ajay Singh 20 6 Trumpet Sonny Muller 20 7 Guitar Farhad Khan 10 9 Guitar Farhad Khan 23 9 Guitar Tommy Jones 23 1 Drums Tommy Jones 5

Problem in Previous Solution  There are a lot of repetition for example the name, address and course.  Also note that where an address is not known, there is no data and this column is NULL.  In order to overcome the problem of repetition, the relation is split into three. This should result in reducing repletion to a minimum.  Only certain attributes are repeated and these are foreign keys that are linking the data in one relation with the data in another.

Normalized Relation Students StudentID Name 1 Guy Smith 2 Sarah Anusiem Address Course History 12 New Street Lagos Modules Foreign keys Computing StudentModules Primary keys ModuleCode Name StudentID ModuleCode Med1 Medieval History 1 1 Med1 OS Operating Systems 1 Med3 Med2 Medieval History 2 1 TCE Net Networks TCE Twentieth Century History 2 OS 2 Net

Normalization  This process of moving from data that is not in a relational form, to a relation is known as normalization.  It is the process of organizing data to minimize redundancy.  In normalization, we divide the database table in two or more tables and create a relationship between them.

Why Normalization?  For Data integrity  To make optimized queries on the normalized tables that produce fast, efficient results.  To increase the performance of the database

Types of Normal Forms 1. First Normal Form(1NF) 2. Second Normal Form (2NF) 3. Third Normal Form (3NF) 4. Boyce-Codd Normal Form (BCNF) 5. Fourth Normal Form (4NF) 6. Fifth Normal Form (5NF)

Relational Integrity Constraints  Relational integrity constraints are used to ensure accuracy and consistency of data in a relational database.  It refers to the different rules that exist within the model to make sure that it is made of relations.  Types 1. Null integrity 2. Entity integrity 3. Referential integrity 4. General constraints

1. Null Integrity  A Null rule is a rule defined on a column that allows or disallows a null (the absence of a value) in that column.  Nulls represent values of an attribute that are unknown. Note that this does NOT mean blank or zero.  Since null means unknown, it is NOT possible to say that an attribute with a value of null is equal to another attribute with a value of null.

1. Null Integrity sp_help tbl_student;

1. Null Integrity This query will produce error because there are already NULL in student_id. So, delete the row having student_id NULL. Try the query again.

1. Null Integrity sp_help tbl_student; Now, try the following query again. See what will happen.

2. Entity Integrity  This rule is about making sure that each tuple (or row) in a relation is unique.  Entity integrity is an integrity rule which states that every table must have a primary key and that the column or columns chosen to be the primary key should be unique and not null.  Why an attribute that is a primary key cannot not be null? Why would this potentially violate uniqueness?  Answer: A null value, being unknown, might be the same as the value in the primary key of another tuple.

Creating Primary Key

Creating Primary Key OR

3. Referential Integrity  The referential integrity constraint is specified between two relations and is used to maintain the consistency among tuples in the two relations.  Referential integrity means if a foreign key is pointing to a record in another table, then that record must exist.  If the foreign key points to a record that doesn't exist, referential integrity is broken.  Referential integrity rule does not imply a foreign key cannot be null.

4. General Constraints  Customized rules specified by the users or database administrators.  It is also called as a business rule which is a statement that defines or constrains some aspect of the business. It is intended to control the behavior of the business.  E.g.: age>=18 && age<=60  It is implemented using CHECK Constraint.

CHECK Constraint  Ensures that the value in a column meets a specific condition.  Enforce domain integrity by limiting the values that are accepted by column(s).  Multiple CHECK constraints can apply to a single column.

CHECK Constraint

Relational Keys 1. Super Key  An attribute, or set of attributes, that uniquely identifies a tuple within a relation.  For example, for the entity Employee = {EID, Name, Address, Age, Salary, Phone No}, the possible super keys are <EID>, <Phone No, Name>, <EID, Name>. 2. Candidate Key  A smallest possible super key.  Only <EID> is a candidate key.  It is called a ‘candidate key’, because it is a candidate to become a primary key 3. Composite Key  Primary Key with more than one attribute.

Functional Dependency Student ID First Name Surname 9901 John Dacus 9902 Satpal Singh 9922 Jagpal Singh 9911 John Smith Students • For any Student ID, there is one first name and one surname, So, First Name and Surname are functionally dependent on Student ID. We can also say Student ID functionally determines First Name and Surname. • Student ID -> First Name, but not the reverse • Student ID -> Surname

Functional Dependency  A functional dependency is a constraint that describes the relationship between attributes in a relation.  If A and B are attributes of relation R, B is said to be functionally dependent on A (denoted A → B), if each value of A is associated with exactly one value of B.  A → B means B is functionally dependent on A or A functionally determines B.

Partial Dependency  A functional dependency A→B is a partially dependency if there is some attribute that can be removed from A and yet the dependency still holds.  When an non-key attribute is determined by a part, but not the whole, of a composite primary key. student_id 1 2 subject_id 1 1 marks 100 80 1 2 85 marks

Transitive Dependency  Three attributes A, B, and C connected in such a way that A→B and B→C. In other words A→C. If we know the value of A, we can determine B, which we can use in turn to determine C. This kind of functional dependency is known as transitive dependency.  e.g. The functional dependency {Book} → {Author Nationality} applies; that is, if we know the book, we know the author's nationality. Furthermore:  {Book} → {Author} {Author} does not → {Book} {Author} → {Author Nationality}  Therefore {Book} → {Author Nationality} is a transitive dependency.

Anomalies 1. Insert Anomalies 2. Update Anomalies 3. Delete Anomalies

Activity: Anomalies Student ID Student Name Activity Fee 9901 Binay Basketball 200 9902 Shyam Football 300 9922 Sitaram Cricket 500 9811 Prashant Football 300 • What information do we lose if Binay quits Basketball? • We would lose the price of ‘Basketball’. • This is the deletion anomaly that occur when relations are not fully normalized. • When you delete some information and lose valuable related information at the same time.

Insert Anomalies  If we want to record a new activity, but no one has yet taken it. Can we insert this information?  We cannot do so; we need a student ID because the student ID is part of the primary key and therefore cannot be null.  This is an insert anomaly.

Update Anomalies  If we wanted to change the cost of football to ‘500’, we would have to do it for every tuple where someone was playing football .  Any change made to your data will require you to scan all records to make the change. This is called the update anomaly.

Normal Forms: Review  Un-normalized – There are multivalued attributes or repeating groups  1 NF – No multivalued attributes or repeating groups.  2 NF – 1 NF plus no partial dependencies  3 NF – 2 NF plus no transitive dependencies

Billing System Bill No.: 1078 Date: 2013-12-20 Customer Code: C100 Customer Name: Ram Shrestha ItemCode ItemName Rate Qty Amount 1 Copy 20 10 200 2 Book 200 8 1600 3 Pen 10 3 30

UNF (Un-Normalized Form) • The first step is to identify which attributes belong to the repeating group. • Those attributes where there is one occurrence are marked with a ‘1’. • Those attributes where there is a repeating group are marked with a ‘2’. • The tentative primary key is also underlined. In this case it is BillNo. UNF UNF Level BillNo 1 Date 1 CustomerCode 1 CustomerName 1 ItemCode 2 ItemName 2 Rate 2 Qty 2 Amount 2

First Normal Form(1NF)  Remove Repeating Group Information BillNo Date CustomerCode CustomerName BillNo ItemCode ItemName Rate Qty Amount

Second Normal Form (2NF)  Remove Partial Key Dependencies  Identify the attributes that are dependent on only one part of the primary key (composite key) and separate them. BillNo Date CustomerCode CustomerName ItemCode ItemName Rate BillNo ItemCode Qty Amount

Third Normal Form (3NF)  Remove Non-Key Dependencies or Transitive Dependencies  Identify the attributes that are functionally dependent on non-key attributes or identify the attributes that are not functionally dependent on primary key.  Here CustomerName is dependent of CustomerCode not BillNo. BillNo Date CustomerCode CustomerCode CustomerName BillNo ItemCode Qty ItemCode ItemName Rate

The Document - Example Student Number: 1078654X Student Name: David Green Course Code: G105 Course Title: BA Business Computing Module Code Module Title BUS119 COM118 COM120 Business Operations Introduction to Computing Application Building Software Engineering Computer Law Systems Analysis COM122 HCI COM110 COM112 COM114 Number of Credits 20 Grade Point Result Code Result 10 P Pass 20 8 P Pass 20 20 3 2 RE DC Refer Exam Defer Coursework 10 20 9 3 P RCE 10 7 P Pass Refer coursework and Exam Pass

UNF UNF UNF Level Student Number 1 Student Name 1 Course Code 1 Course Title 1 Module Code 2 Module Title 2 No. of Credits 2 Grade Point 2 Result Code 2 Result 2 • The first step is to identify which attributes belong to the repeating group. • Those attributes where there is one occurrence are marked with a ‘1’. • Those attributes where there is a repeating group are marked with a ‘2’. • The tentative primary key is also underlined. In this case it is student number.

First Normal Form(1NF)  Remove Repeating Group Information Student Number Student Name Course Code Course Title Student Number Module Code Module Title No. of Credits Grade Point Result Code Result

Second Normal Form (2NF)  Remove Partial Key Dependencies Student Number Student Name Course Code Course Title Module Code Module Title No. of Credits Student Number Module Code Grade Point Result Code Result

Third Normal Form (3NF)  Remove Non-Key Dependencies or Transitive Dependencies Student Number Student Name Course Code Course Code Course Title Module Code Module Title No. of Credits Student Number Module Code Grade Point Result Code Result Code Result

Activity 1

Activity 2

Activity 3


References  on/2.2.4_1NF%20Repeating%20Attributes.html  on/2.2.5_2NF-Partial%20Dependancy.html  on/2.2.6_3NF-Transitive%20Dependency.html   

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