Data Management. Information Technology For Management 7 th Edition Turban & Volonino Based on lecture slides by L. Beaubien, Providence College

Transcription

1 Chapter 3 Data Management Information Technology For Management 7 th Edition Turban & Volonino Based on lecture slides by L. Beaubien, Providence College John Wiley & Sons, Inc. Chapter 3 1

2 Data Management Difficulties with managing data Amount of data is increasing Data is scattered throughout the organization Legal regulations Data quality and security Solutions to managing data File Management Database Management Systems (DBMS) Data Warehousing and Analytical Processing Chapter 3 2

3 Data Sources Organizational data Internal data on customers, products,... End-user data Maintained in de-centralized way, personal contacts, estimates,... External data Stock quotes, reports, academic papers,... Chapter 3 3

4 Data Quality Accuracy, accessibility, relevance, timeliness and completeness Inconsistent or incorrect data Redundant data Stolen data Missing data Steps: standardization, verification, matching, ehancement Chapter 3 4

5 Data Hierarchy The Data Hierarchy: A bit represents the smallest unit of data a computer can process (a 0 or a 1); a byte, represents a single character, which can be a letter, a number, or a symbol. Field: A logical grouping of characters into a word, a small group of words, or a complete number. Record: A logical grouping of related fields. File: A logical grouping of related records. Database: A logical grouping of related files. Chapter 3 5

6 The Traditional Approach To Data Management Chapter 3 6

7 Databases A database is an organized logical grouping of related files. Centralized databases - all the related files are located in one physical location Distributed database Replicated database Partitioned database Considerations Failure Access speed Maintaining consistency Security Chapter 3 7

8 The Database Approach to Data Management - Database Management Systems (DBMS) Chapter 3 8

9 Advantages of DBMS Persistence Query ability Concurrency Backup and replication Rule enforcement Security Computation Logging Chapter 3 9

10 DBMS (cont d) DBMS provides the ability for many users to share and process data by providing two views of the database Physical view (for expert in maintenance) Logical view (user view) DBMS Languages Data Definition Language Data Manipulation Language SQL Structured Query Language Chapter 3 10

11 Creating Databases Step 1: Data Model Entity-Relationship Diagram (ERD) Abstract model for data and their relationships Step 2: Data Tables Derived from data model Based on one general model for databases (e.g. Relational model) Chapter 3 11

12 Data Model and ERD Entity Type collection of entities that share common properties or characteristics Person, place, object... Attribute - property or characteristic of an entity type that is of interest to the organization Name, address,... Identifier uniquely identifies an entity instance Relationship type link (association) between entity types Chapter 3 12

13 Data Model and ERD Entity symbols A special entity that is also a relationship Attribute symbols Several slightly different notations exist... Chapter 3 13

14 Data Model and ERD Relationships Degree (unary, binary,...) depending on entities involved Chapter 3 14

15 Data Model and ERD Relationships Cardinality (one-to-one, one-to-many, manyto-many) depending on matching One-to-one: Husband Wife One-to-Many: Teacher Student Many-to-Many: Student - Course Chapter 3 15

16 Data Model and ERD Example Id Name Grade Student takes Course advises uses Professor Textbook Chapter 3 16

17 Data Model and ERD Example Id Name Grade Student m takes n Course m 1 advises 1 Professor uses 1 Textbook Chapter 3 17

18 ERD - Example Prepare an ERD for the following situation: A supermarket wants to store its data in a database. They have several branches, each with an adress, and employees are assigned to one branch each. Products (like milk, bread,...) can be offered in several branches, and customers will buy products on certain dates. Think of suitable attributes. Chapter 3 18

19 ERD - Example Prepare an ERD for the following situation: A consulting company maintains offices in several countries. Each office can have several employees assigned, each employee is assigned to one office. Each employee is managed by another employee. Customers offer projects to the company, each project is from one customer. Employees work on the project for a given time and intensity, and can work on more than one project at the same time. A project will have several employees assigned. For each project, there can be several invoices with different amounts and dates. Chapter 3 19

20 Relational Models Describe data using a standard tabular format with all data elements placed in twodimensional tables. Entity: translates to table Attribute: translates to field Chapter 3 20

21 Relational Models Relationship: stored by using the identifiers (keys), storing them as references (foreign keys) at other tables depends on cardinality 1-to-1: identifier of one side is included in other side (Course: id, time, textbook-id) 1-to-m: identifier of 1-side included in other side (Student: id, name, advisor-id) N-to-m: separate table with both identifiers (Takes: student-id, course-id, grade) Chapter 3 21

22 Relational Models - Example Describe the tables from the Supermarket / Consulting Company ERD. Chapter 3 22