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Relational Databases Chapter 4 Copyright © 2015 Pearson Education, Inc. 4-1 INTRODUCTION • Relational databases underlie most modern integrated AISs. ▫ They are the most popular type of database used for transaction processing. Copyright © 2015 Pearson Education, Inc. 4-2 What Is a Database? • Efficiently and centrally coordinates information for a related group of files • A file is a related group of records • A record is a related group of fields • A field is a specific attribute of interest for the entity (record) Copyright © 2015 Pearson Education, Inc. 4-3 FILE VS. DATABASES • Database systems were developed to address the problems associated with the proliferation of master files. ▫ For years, each time a new information need arose, companies created new files and programs. ▫ The result: a significant increase in the number of master files. Copyright © 2015 Pearson Education, Inc. 4-4 FILE VS. DATABASES Master File 1 Fact A Fact B Fact C Fact D Master File 2 Fact A Fact C Fact E Fact F Sales Program Shipping Program Billing Master File 3 Program Fact A Fact D Fact E Copyright © 2015 Pearson Education, Inc. Fact G • This proliferation of master files created problems: ▫ Often the same information was stored in multiple master files. ▫ Made it more difficult to effectively integrate data and obtain an organization-wide view of the data. ▫ Also, the same information may not have been consistent between files. If a customer changed their phone number, it may have been updated in one master file but not another. 4-5 FILE VS. DATABASES • A database is a set of inter-related, centrally coordinated files. Database Fact A Fact B Fact C Fact D Fact E Fact F Fact G Database Management System Sales Program Shipping Program Copyright © 2015 Pearson Education, Inc. Billing Program 4-6 FILE VS. DATABASES Database Fact A Fact B Fact C Fact D Fact E Fact F Fact G Database Management System Sales Program Shipping Program Copyright © 2015 Pearson Education, Inc. Billing Program • The database approach treats data as an organizational resource that should be used by and managed for the entire organization, not just a particular department. • A database management system (DBMS) serves as the interface between the database and the various application programs. 4-7 FILE VS. DATABASES Database Fact A Fact B Fact C Fact D Fact E Fact F Fact G Database Management System Sales Program Shipping Program Copyright © 2015 Pearson Education, Inc. Billing Program • The combination of the database, the DBMS, and the application programs that access the database is referred to as the database system. 4-8 FILE VS. DATABASES Database Fact A Fact B Fact C Fact D Fact E Fact F Fact G Database Management System Sales Program Shipping Program Copyright © 2015 Pearson Education, Inc. Billing Program • The person responsible for the database is the database administrator. • As technology improves, many large companies are developing very large databases called data warehouses. • Data Mining Analysis to identify relationships in the data, new knowledge about business processes, etc. Example, Credit card issuers efforts to defect fraud 4-9 FILE VS. DATABASES Master File 1 Fact A Fact B Fact C Fact D Master File 2 Fact A Fact C Fact E Fact F Sales Program Database Fact A Fact B Fact C Fact D Fact E Fact F Fact G Shipping Program Database Management System Billing Master File 3 Program Fact A Fact D Fact E Copyright © 2015 Pearson Education, Inc. Fact G Sales Program Shipping Program Billing Program 4-10 Advantages of Database Systems • Data Integration ▫ Files are logically combined and made accessible to various systems. • Data Sharing ▫ With data in one place it is more easily accessed by authorized users. • Reporting flexibility: Reports can be revised easily and generated as needed and the database can be easily browsed to research a problem or obtain detailed information underlying a summary report Copyright © 2015 Pearson Education, Inc. 4-11 Advantages of Database Systems • Minimizing Data Redundancy and Data Inconsistency ▫ Eliminates the same data being stored in multiple files, thus reducing inconsistency in multiple versions of the same data. • Data Independence ▫ Data is separate from the programs that access it. Changes can be made to the data without necessitating a change in the programs and vice versa Copyright © 2015 Pearson Education, Inc. 4-12 Advantages of Database Systems • Central management of data: ▫ Data management is more efficient because a database administrator is responsible for coordinating, controlling and managing data • Cross-Functional Analysis ▫ Relationships between data from various organizational departments can be more easily combined. Example: association between sales and promotional campaigns Copyright © 2015 Pearson Education, Inc. 4-13 Advantages of Database Systems • One-time Data Entry and Storage: ▫ In the data-base approach to data management data are input into the data base once, stored in a particular location and available for use my multiple applications and users Copyright © 2015 Pearson Education, Inc. 4-14 IMPORTANCE AND ADVANTAGES OF DATABASE SYSTEMS • The importance of good data: ▫ Bad data leads to: Bad decisions Embarrassment Angry users Copyright © 2015 Pearson Education, Inc. 4-15 Database Users and Designers • Different users of the database information are at an external level of the database. These users have logical views of the data. • At an internal level of the database is the physical view of the data which is how the data is actually physically stored in the system. • Designers of a database need to understand user’s needs and the conceptual level of the entire database as well as the physical view. Copyright © 2015 Pearson Education, Inc. 4-16 Physical View • Physical views of data ▫ In file-oriented systems, programmers must know the physical location and layout of records used by a program. They must reference the location, length, and format of every field they utilize. When data is used from several files, this process becomes more complex. Copyright © 2015 Pearson Education, Inc. 4-17 Physical View Copyright © 2015 Pearson Education, Inc. 4-18 Copyright © 2015 Pearson Education, Inc. 4-19 Schemas • Describe the logical structure of a database ▫ Conceptual Level Organization wide view of the data ▫ External Level Individual users view of the data Each view is a subschema ▫ Internal Level Describes how data are stored and accessed Description of: records, definitions, addresses, and indexes Copyright © 2015 Pearson Education, Inc. 4-20 4-20 Database Design • To design a database, you need to have a conceptual view of the entire database. • The conceptual view illustrates the different files and relationships between the files. • The data dictionary is a “blueprint” of the structure of the database and includes data elements, field types, programs that use the data element, outputs, and so on. Copyright © 2015 Pearson Education, Inc. 4-21 4-22 The Data Dictionary Copyright © 2015 Pearson Education, Inc. DBMS Languages • Data Definition Language (DDL) ▫ Builds the data dictionary ▫ Creates the database ▫ Describes logical views for each user ▫ Specifies record or field security constraints • Data Manipulation Language (DML) ▫ Changes the content in the database Creates, updates, insertions, and deletions • Data Query Language (DQL) ▫ Enables users to retrieve, sort, and display specific data from the database • Report Writer ▫ Simplifies report creation Copyright © 2015 Pearson Education, Inc. 4-23 Relational Database • Represents the conceptual and external schema as if that “data view” were truly stored in one table. • Although the conceptual view appears to the user that this information is in one big table, it really is a set of tables that relate to one another. Copyright © 2015 Pearson Education, Inc. 4-24 Conceptual View Example Customer Name Sales Invoice # Invoice Total D. Ainge 101 $1,447 G. Kite 102 $4,394 D. Ainge 103 $ 898 G. Kite 104 $ 789 F. Roberts 105 $3,994 Copyright © 2015 Pearson Education, Inc. 4-25 Types of Attributes • Primary key ▫ is the attribute, or combination of attributes, that uniquely identifies a specific row(record) in a table. • Foreign key ▫ is an attribute in a table that is a primary key in another table. ▫ Foreign keys are used to link tables. • Other Non Key Attributes ▫ Store other important data about the entity Copyright © 2015 Pearson Education, Inc. 4-26 Relational Data Tables Invoice # is PK Customer # is PK Item # is PK Combination of Invoice # & Item # forms the PK Copyright © 2015 Pearson Education, Inc. 4-26 Relational Data Tables Primary Keys Foreign Key (Customer # is a Foreign key in the Sales Table because it is a Primary key that uniquely identifies Customers in the Customer Table). Because of this, the Sales Table can relate to the Customer Table (see red arrow above). Copyright © 2015 Pearson Education, Inc. 4-28 Why Have a Set of Related Tables? • Data stored in one large table can be redundant and inefficient causing the following problems: ▫ Update anomaly Changes to existing data are not correctly recorded. Due to multiple records with the same data attributes ▫ Insert anomaly Unable to add a record to the database. ▫ Delete anomaly Removing a record also removes unintended data from the database. Copyright © 2015 Pearson Education, Inc. 4-29 Database Design Errors • Alternatives for storing data ▫ One possible alternate approach would be to store all data in one uniform table. ▫ For example, instead of separate tables for students and classes at a University, we could store all data in one table and have a separate line for each student x class combination. Copyright © 2015 Pearson Education, Inc. 4-30 Student ID Last Name First Name Phone No. 333-33-3333 Simpson Alice 333-3333 ACCT-3603 1 M 9:00 AM 333-33-3333 Simpson Alice 333-3333 FIN-3213 3 Th 11:00 AM 333-33-3333 Simpson Alice 333-3333 MGMT-3021 11 Th 12:00 PM 111-11-1111 Sanders Ned 444-4444 ACCT-3433 2 T 10:00 AM 111-11-1111 Sanders Ned 444-4444 MGMT-3021 5 W 8:00 AM 111-11-1111 Sanders Ned 444-4444 ANSI-1422 7 F 9:00 AM 123-45-6789 Moore Artie 555-5555 ACCT-3433 2 T 10:00 AM 123-45-6789 Moore Artie 555-5555 FIN-3213 3 Th 11:00 AM Course No. Section Day Time • Using the suggested approach, a student taking three classes would need three rows in the table. • In the above, simplified example, a number of problems arise. Copyright © 2015 Pearson Education, Inc. 4-31 Student ID Last Name First Name Phone No. 333-33-3333 Simpson Alice 333-3333 ACCT-3603 1 M 9:00 AM 333-33-3333 Simpson Alice 333-3333 FIN-3213 3 Th 11:00 AM 333-33-3333 Simpson Alice 333-3333 MGMT-3021 11 Th 12:00 PM 111-11-1111 Sanders Ned 444-4444 ACCT-3433 2 T 10:00 AM 111-11-1111 Sanders Ned 444-4444 MGMT-3021 5 W 8:00 AM 111-11-1111 Sanders Ned 444-4444 ANSI-1422 7 F 9:00 AM 123-45-6789 Moore Artie 555-5555 ACCT-3433 2 T 10:00 AM 123-45-6789 Moore Artie 555-5555 FIN-3213 3 Th 11:00 AM Course No. Section Day Time • Suppose Alice Simpson changes her phone number. You need to make the change in three places. If you fail to change it in all three places or change it incorrectly in one place, then the records for Alice will be inconsistent. • This problem is referred to as an update anomaly. Copyright © 2015 Pearson Education, Inc. 4-32 Student ID Last Name First Name Phone No. 333-33-3333 Simpson Alice 333-3333 ACCT-3603 1 M 9:00 AM 333-33-3333 Simpson Alice 333-3333 FIN-3213 3 Th 11:00 AM 333-33-3333 Simpson Alice 333-3333 MGMT-3021 11 Th 12:00 PM 111-11-1111 Sanders Ned 444-4444 ACCT-3433 2 T 10:00 AM 111-11-1111 Sanders Ned 444-4444 MGMT-3021 5 W 8:00 AM 111-11-1111 Sanders Ned 444-4444 ANSI-1422 7 F 9:00 AM 123-45-6789 Moore Artie 555-5555 ACCT-3433 2 T 10:00 AM 123-45-6789 Moore Artie 555-5555 FIN-3213 3 Th 11:00 AM Course No. Section Day Time • What happens if you have a new student to add, but he hasn’t signed up for any courses yet? • Or what if there is a new class to add, but there are no students enrolled in it yet? In either case, the record will be partially blank. • This problem is referred to as an insert anomaly. Copyright © 2015 Pearson Education, Inc. 4-33 Student ID Last Name First Name Phone No. 333-33-3333 Simpson Alice 333-3333 ACCT-3603 1 M 9:00 AM 333-33-3333 Simpson Alice 333-3333 FIN-3213 3 Th 11:00 AM 333-33-3333 Simpson Alice 333-3333 MGMT-3021 11 Th 12:00 PM 111-11-1111 Sanders Ned 444-4444 ACCT-3433 2 T 10:00 AM 111-11-1111 Sanders Ned 444-4444 MGMT-3021 5 W 8:00 AM 111-11-1111 Sanders Ned 444-4444 ANSI-1422 7 F 9:00 AM 123-45-6789 Moore Artie 555-5555 ACCT-3433 2 T 10:00 AM 123-45-6789 Moore Artie 555-5555 FIN-3213 3 Th 11:00 AM Course No. Section Day Time • If Ned withdraws from all his classes and you eliminate all three of his rows from the table, then you will no longer have a record of Ned. If Ned is planning to take classes next semester, then you probably didn’t really want to delete all records of him. • This problem is referred to as a delete anomaly. Copyright © 2015 Pearson Education, Inc. 4-34 Database Design Errors • Alternatives for storing data ▫ Another possible approach would be to store each student in one row of the table and create multiple columns to accommodate each class that he is taking. Copyright © 2015 Pearson Education, Inc. 4-35 Student ID Last Name First Name Phone No. 333-33-3333 Simpson Alice 333-3333 ACCT-3603 FIN-3213 MGMT-3021 111-11-1111 Sanders Ned 444-4444 ACCT-3433 MGMT-3021 ANSI-1422 123-45-6789 Moore Artie 555-5555 ACCT-3433 FIN-3213 Class 1 Class 2 Class 3 Class 4 • This approach is also fraught with problems: – How many classes should you allow in building the table? – The above table is quite simplified. In reality, you might need to allow for 20 or more classes (assuming a student could take many 1hour classes). Also, more information than just the course number would be stored for each class. There would be a great deal of wasted space for all the students taking fewer than the maximum possible number of classes. – Also, if you wanted a list of every student taking MGMT-3021, notice that you would have to search multiple attributes. Copyright © 2015 Pearson Education, Inc. 4-36 Student ID 333-33-3333 111-11-1111 123-45-6789 STUDENTS Last First Name Name Simpson Alice Sanders Ned Moore Artie Course ID Course 1234 ACCT-3603 1235 ACCT-3603 1236 MGMT-2103 Student x Course Student ID Course ID 1234 333333333 1236 333333333 1235 111111111 1236 111111111 Copyright © 2015 Pearson Education, Inc. COURSES Section 1 2 1 Phone No. 333-3333 444-4444 555-5555 Day MWF TR MW Time 8:30 9:30 8:30 • The solution to the preceding problems is to use a set of tables in a relational database. • Each entity is stored in a separate table, and separate tables or foreign keys can be used to link the entities together. 4-37 Relational Database Design Rules • Every column in a row must be single valued • Primary key cannot be null (empty) also known as entity integrity • IF a foreign key is not null, it must have a value that corresponds to the value of a primary key in another table (referential integrity) • All other attributes in the table must describe characteristics of the object identified by the primary key Following these rules allows databases to be normalized and solves the update, insert, and delete anomalies. Copyright © 2015 Pearson Education, Inc. 4-38 Basic requirements of a relational database •Every column(field) in a row must be single valued. •In other words, every cell can have one and only one value. student # course # name name address (1,N) STUDENT (1,N) TAKES COURSE Student# Name Address Course# * 1 Tony Cleveland Acg4401, Acg3101 2 Emily New York Acg4401, Acg3101 3 Leigh Birmingham Acg4401, Acg3101 Course# Name Student#* Acg4401 AIS 1, 2, 3 Acg3101 FAR 1 1, 2, 3 4-39 • Note that within each table, there are no duplicate primary keys and no null primary keys. • Consistent with the entity integrity rule. student # course # name name address (1,N) STUDENT (1,N) COURSE TAKES Student# Name Address Student# Course# 1 Tony Cleveland 1 Acg4401 2 Emily New York 1 Acg3101 3 Leigh Birmingham 2 Acg4401 Course# Name 2 Acg3101 Acg4401 AIS 3 Acg3101 Acg3101 FAR 1 Relationship Table Copyright © 2015 Pearson Education, Inc. 4-40 FK example Not in Salesperson Table Referential integrity would prevent this from happening 4-41 RELATIONAL DATABASES • An important feature is that data about various things of interest (entities) are stored in separate tables. ▫ Makes it easier to add new data to the system. You add a new student by adding a row to the student table. You add a new course by adding a row to the course table. Means you can add a student even if he hasn’t signed up for any courses. And you can add a class even if no students are yet enrolled in it. ▫ Makes it easy to avoid the insert anomaly. • Space is also used more efficiently than in the other schemes. There should be no blank rows or attributes. Copyright © 2015 Pearson Education, Inc. 4-42 Student ID 333-33-3333 111-11-1111 123-45-6789 STUDENTS Last First Name Name Simpson Alice Sanders Ned Moore Artie Course ID Course 1234 ACCT-3603 1235 ACCT-3603 1236 MGMT-2103 Student x Course Student ID Course ID 1234 333333333 1236 333333333 1235 111111111 1236 111111111 Copyright © 2015 Pearson Education, Inc. Phone No. 333-3333 444-4444 555-5555 COURSES Section 1 2 1 Day MWF TR MW • Add a student here. • Leaves no blank spaces. Time 8:30 9:30 8:30 • Add a course here. • Leaves no blank spaces. • When a particular student enrolls for a particular course, add that info here. 4-43 RELATIONAL DATABASES • Deletion of a class for a student would cause the elimination of one record in the student x class table. ▫ The student still exists in the student table. ▫ The class still exists in the class table. ▫ Avoids the delete anomaly. Copyright © 2015 Pearson Education, Inc. 4-44 Student ID 333-33-3333 111-11-1111 123-45-6789 STUDENTS Last First Name Name Simpson Alice Sanders Ned Moore Artie Course ID Course 1234 ACCT-3603 1235 ACCT-3603 1236 MGMT-2103 Student x Course Student ID Course ID 1234 333333333 1236 333333333 1235 111111111 1236 111111111 Copyright © 2015 Pearson Education, Inc. Phone No. 333-3333 444-4444 555-5555 COURSES Section 1 2 1 Day MWF TR MW • Ned still exists in the student table. Time 8:30 9:30 8:30 • Even if Ned was the only student in the class, ACCT-3603 still exists in the course table. • If Ned Sanders drops ACCT-3603, remove Ned’s class from this table. 4-45 Database Design • There are two basic ways to design wellstructured relational databases. ▫ Normalization ▫ Semantic data modeling(chapter 17) Copyright © 2015 Pearson Education, Inc. 4-46 Normalizing Relational Databases • Initially, one table is used for all the data in a database. • Following rules, the table is decomposed into multiple tables related by: ▫ Primary key–foreign key integration • Decomposed set of tables are in third normal form (3NF). Copyright © 2015 Pearson Education, Inc. 4-47 Table 4-14 page 103 FK Requested Mortgage Amount Lender Number 450 Peachtree Rd. $245,000 David 500 Loop Highway Bronson Paul 453 Brown 454 4-48 FK Lender Name Lender Office Address 13 Excel Mortgage 6890 Sheridan Dr. 8 Advent Appraisers $124,688 I3 Excel Mortgage 6890 Sheridan Dr. 9 Independent Appraisal Service 312 Mountain View Dr. $345,000 14 CCY 28 Buckhead Way 10 Jones Property Appraisers Marietta 310 Loop Highway $ 57,090 15 Advantage Lenders 3345 Lake Shore Dr. 10 Jones Property Appraisers Charles Kenneth 3 Commons Blvd. $ 34,000 16 Capital Savings 8890 Coral Blvd. - 8 Advent Appraisers 455 Coulter Tracey 1367 Peachtree Rd. $216,505 13 Excel Mortgage 6890 Sheridan Dr. 8 Advent Appraisers 456 Foster Harold 678 Loop Highway $117,090 12 National Mortgage 750 16 St. 9 Independent Appraisal Service 457 Frank Vernon 210 Bicayne Blvd. $ 89,000 12 National Mortgage 750 16 St. 10 458 Holmes Heather 1121 Bicayne Blvd. $459,010 16 Capital Savings 8890 Coral Blvd. 10 459 Johanson Sandy 817 Mountain View Dr. $ 67,900 15 Advantage Lenders 3345 Lake Shore Dr. 9 460 Johnson James 985 Loop Highway $ 12,000 12 National Mortgage 750 16 St. 10 461 Jones Holly 1650 Washington Blvd. $ 67,890 15 Advantage Lenders 3345 Lake Shore Dr. 9 Borrower Number Last Name First Name Current Address 450 Adams Jennifer 451 Adamson 452 ' Property Appraiser Number Property Appraiser Name Jones Property Appraisers Jones Property Appraisers Independent Appraisal Service Jones Property Appraisers Independent Appraisal Service Solution page 112 Borrower Number 450 451 452 453 454 455 456 457 458 459 460 461 Lender Number 12 13 14 15 16 Last Name Adams Adamson Bronson Brown Charles Coulter Foster Frank Holmes Johanson Johnson Jones First Name Jennifer David Paul Marietta Kenneth Tracey Harold Vernon Heather Sandy James Holly Lender Name National Mortgage Excel Mortgage CCY Advantage Lenders Capital Savings Requested Mortgage Current Address Amount 450 Peachtree Rd. $245,000 500 Loop Highway $124,688 312 Mountain View Dr. $345,000 310 Loop Highway $57,090 3 Commons Blvd. $34,000 1367 Peachtree Rd. $216,505 678 Loop Highway $117,090 210 Bicayne Blvd. $89,000 1121 Bicayne Blvd. $459,010 817 Mountain View Dr. $67,900 985 Loop Highway $12,000 1650 Washington Blvd. $67,890 Lender Address 750 16 St. 6890 Sheridan Dr. 28 Buckhead Way 3345 Lake Shore Dr. 8890 Coral Blvd. Lender Property Number Appraiser Number 13 8 13 9 14 10 15 10 16 8 13 8 12 9 12 10 16 10 15 9 12 10 15 9 Property Appraiser Number 8 9 10 Property Appraiser Name Advent Appraisers Independent Appraisal Service Jones Property Appraisers 49 Primary key/Foreign Key • Establishing relationship • Primary key/Foreign key must be like type data types ▫ Auto# cannot be FK because it can only be used one time Copyright © 2015 Pearson Education, Inc. Data Type PK FK auto# Auto# NO Auto# Number Yes Number Auto# NO Number Number Yes Number Text NO Text Text Yes Text Number NO 50