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What Is Database Normalization ?

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What Is Database Normalization ? Data : Content that is entered into system Field : A character or group of characters (alphabetic or numeric) that has a specific meaning. Record : A logically connected set of one or more fields that describes a person, place, or thing. File : A collection of records. File: A collection of records or documents dealing with one organization, person, area or subject. Manual (paper) files Computer files Files dedicated to application programs Data Inconsistency . It Occurs When The Same data Doesn’t match each other In Various Relations(Tables). Data redundancy . It refers duplication of information in different files Difficulty in accessing data . Need to write a new program to carry out each new task Database is a structured set of data held in a computer, especially one that is accessible in various ways. A database management system (DBMS) is a collection of programs that enables you to store, modify, and extract information from a database. PC databases Centralized database Distributed databases This type of data base is used for single PC. Eg- MS-Access, foxpro. This type of data base supports client/server network architecture. Eg- oracle. Database Database Server This architecture contains many local servers spread across geographical areas. DBMS =============== Design tools Table Creation Form Creation Query Creation Application Report Creation Programs Database Procedural language compiler (4GL) Database contains: ============= User’s Data Run time User Metadata Form processor Interface Query processor Applications Report Writer Language Run time BACK FRONT END END Data dictionary A DBMS component that stores metadata, contains a list of all files in a database, the number of records in each file. Metadata is data about data. It is descriptive information about a particular data set or object. Query processing refers the retrieval of information from a database. Report writer Also called a report generator, a program, usually part of a database management system, that extracts information from one or more files and presents the information in a specified format. You can also format data into pie charts, bar charts, and other diagrams. Physical level: . describes how a record (e.g., customer) is stored. Logical level: . describes data stored in database, and the relationships among the data. View level: . application programs hide details of data types. It refers that changing of data in one level does not affect in the data of another next level. If we do some changes on table format, it should not change the data residing on the disk. It is the power to change the physical data without impacting the schema or logical data. Schema – the logical structure of the database . Physical schema: database design at the physical level . Logical schema: database design at the logical level Instance – the actual content of the database at a particular point in time A collection of tools for describing data and data relationships. Types of models : . Object-Oriented Model . Hierarchical Model . Network Model or Codasyl Model . E R Model . Relational Model A hierarchical database is a design that uses a one-to- many relationship for data elements. Hierarchical database model uses a tree structure. Limitation: Many to Many Relationship Does not exist. Similar to the hierarchical database with the implementation of many-to-many relationships. • In the object oriented data model the (OODM), both data and their relationship are contained in a single structure known us an object. • An object is the abstraction of the real- word entity. An object represents only one occurrence of entity. • Attributes describe the property of an object. • Objects that are similar in characteristics are grouped in class. • Class: is a collection of similar objects with shared structure ( attributes) and behavior (method) • Method: represents areal word action such as finding a selected person’s name, changing person’s name or printing a persons address. • Classes are organized in class hierarchy. The class hierarchy resembles an up side down tree in which each class has only one parent. PARENT PERSON CUSTOMER EMPLOYEE • Inheritance is the ability of an object within the class hierarchy to inherit the attributes and methods of the class above it. INVOICE • Unified modeling language : INV__DATE describes a set of diagrams INV__NUMBER INV__SHP__DATE and symbols that can be used INV__TOTAL to graphically model a system. CUSTOMER 1 LINE M The entity-relationship model (or ER model) is a way of graphically representing the logical relationships of entities (or objects) in order to create a database. A database can be modeled as: • a collection of entities, • relationship among entities. An entity is an object that exists and is distinguishable from other objects. • Example: specific person, company, event, plant Entities have attributes • Example: a person or a book An entity set is a set of entities of the same type that share the same properties. • Example: all persons having an account at a bank. Domain – the set of permitted values for each attribute Attribute types: Simple and composite attributes. Single-valued and multi-valued attributes E.g. multivalued attribute: phone-numbers Derived attributes Can be computed from other attributes. E.g. age, given date of birth Degree of Relationship Set Refers to number of entity set that participate in a relationship set. Binary : Relationship set that involve two entity sets. Ternary : Relationship sets may involve more than two entity sets. Mapping Cardinalities Express the number of entities to which another entity can be associated via a relationship set. Most useful in describing binary relationship sets. For a binary relationship set, the mapping cardinality must be one of the following types: One to one One to many Many to one Many to many Mapping Cardinalities One to one One to many Some elements in A and B may not be mapped to any elements in the other set. Mapping Cardinalities Many to one Many to many Some elements in A and B may not be mapped to any elements in the other set Rectangles represent entity sets. Diamonds represent relationship sets. Lines link attributes to entity sets and entity sets to relationship sets. Ellipses represent attributes Double ellipses represent multivalued attributes. Dashed ellipses denote derived attributes. Underline indicates primary key attributes Weak Entity Set An entity set that does not have a primary key is referred to as a weak entity set. We depict a weak entity set by double rectangles. We underline the discriminator of a weak entity set with a dash Identifying relationship depicted using a double diamonded line. payment-number – discriminator of the payment entity set Primary key for payment – (loan-number, payment- number) Generalization It is a bottom-up approach in which two lower level entities combine to form a higher level entity. Specialization It is opposite to Generalization. It is a top-down approach in which one higher level entity can be broken down into two lower level entity. Aggregation It is a process when relation between two entity is treated as a single entity. Here the relation between Centre and Course, is acting as an Entity in relation with Visitor. Super key is a set of one or more attributes whose values uniquely determine each entity in the entity set. Candidate key is a minimal super key in the entity set. Data stored in tables that are associated by shared attributes (keys). Developed by E.F. Codd, C.J. Date (70s) Table = Entity = Relation Table row = tuple = instance Table column = attribute Attributes Cust_Id Cust_Name Street City Acc_NO 1000 Ravi Lohia gorakhpur A-05 marg tuples 1001 Shobhit Ashok Lucknow A-10 marg 1002 Gaurav Gokhle Faridabad A-11 marg 1003 Arindom Pk sen Kanpur A-12 road 1004 Neeraj Cantt chandigarh A-13 road Entity . Object, Concept or event (subject) Attribute . a Characteristic of an entity Tuple . represents a record Degree total number of attributes Cardinality . total number of tuples A key of a relation is a subset of attributes with the following attributes: Unique identification Non-redundancy Super Key Super Key is defined as a set of attributes within a table that uniquely identifies each record within a table. Super Key is a superset of Candidate key. Candidate Key Candidate keys are defined as the set of fields from which primary key can be selected. It is an attribute or set of attribute that can act as a primary key for a table to uniquely identify each record in that table. Primary key It is used to identify a record uniquely in a database Secondary or Alternative key The candidate key which are not selected for primary key are known as secondary keys or alternative keys Composite Key Key that consist of two or more attributes that uniquely identify an entity occurrence is called Composite key. Foreign Key A foreign key is generally a primary key from one table that appears as a field in another where the first table has a relationship to the second. Table A Name Address Parcel # John Smith 18 Lawyers Dr. 756554 T. Brown 14 Summers Tr. 887419 Table B Parcel # Assessed Value 887419 152,000 446397 100,000 Referential integrity concerns two or more tables that are related. Example: IF table A contains a foreign key that matches the primary key of table B THEN values of this foreign key either match the value of the primary key for a row in table B or must be null. WHAT IS DATABASE NORMALIZATION ? • Database Normalization is a technique of organizing the data in the database. • Normalization is a systematic approach of decomposing tables to eliminate data redundancy and undesirable characteristics like Insertion, Update and Deletion Anomalies. • Normalization is used for mainly two purpose, Eliminating redundant (useless) data. Ensuring data dependencies make sense i.e data is logically stored. PROBLEM WITHOUT NORMALIZATION! • Without Normalization, it becomes difficult to handle and update the database, without facing data loss.
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