CHAPTER 6 DATA DESIGN

Chapter Objectives Explain data design concepts and structures Describe file processing systems Explain database systems and define the components of a database management system (DBMS) Describe Web-based data design 3

Chapter Objectives Explain data design terminology, including entities, fields, common fields, records, files, tables, and key fields Describe data relationships, draw an entity relationship diagram, define cardinality, and use cardinality notation Explain the concept of normalization Explain the importance of codes and describe various coding schemes 3

Chapter Objectives Describe relational and object-oriented database models Explain data warehousing and data mining Differentiate between logical and physical storage and records Explain data control measures

Introduction You will develop a physical plan for data organization, storage, and retrieval Begins with a review of data design concepts and terminology, then discusses file-based systems and database systems, including Web-based databases Concludes with a discussion of data storage and access, including strategic tools such as data warehousing and data mining, physical design issues, logical and physical records, data storage formats, and data controls 4

Data Design Concepts Before constructing an information system, a systems analyst must understand basic design concepts, including data structures and the characteristics of file processing and database systems, including Web-based database design

Data Design Concepts Data Structures Each file or table contains data about people, places, things or events that interact with the information system File-oriented system File processing system Database system

Data Design Concepts Overview of File Processing Some companies still use file processing to handle large volumes of structured data on a regular basis Although much less common today, file processing can be efficient and cost-effective in certain situations

Data Design Concepts Overview of File Processing Potential problems Data redundancy Data integrity Rigid data structure

Data Design Concepts Overview of File Processing Various types of files Master file Table file Transaction file Work file Security file History file

Data Design Concepts The Evolution from File Systems to Database Systems A properly designed database system offers a solution to the problems of file processing Provides an overall framework that avoids data redundancy and supports a real-time, dynamic environment

Data Design Concepts The Evolution from File Systems to Database Systems A database management system (DBMS) is a collection of tools, features, and interfaces that enables users to add, update, manage, access, and analyze the contents of a database The main advantage of a DBMS is that it offers timely, interactive, and flexible data access

Data Design Concepts The Evolution from File Systems to Database Systems Advantages Scalability Better support for client/server systems Economy of scale Flexible data sharing Enterprise-wide application – database administrator (DBA) Stronger standards

Data Design Concepts The Evolution from File Systems to Database Systems Advantages Controlled redundancy Better security Increased programmer productivity Data independence

Data Design Concepts The Evolution from File Systems to Database Systems Although the trend is toward enterprise-wide database design, many companies still use a combination of centralized DBMSs and smaller, department-level database systems The compromise, in many cases, is a client/server design, where processing is shared among several computers

DBMS Components A DBMS provides an interface between a database and users who need to access the data In addition to interfaces for users, database administrators, and related systems, a DBMS also has a data manipulation language, a schema and subschemas, and a physical data repository

DBMS Components Interfaces for Users, Database Administrators, and Related Systems Users Query language Query by example (QBE) SQL (structured query language) Database Administrators A DBA is responsible for DBMS management and support

DBMS Components Interfaces for Users, Database Administrators, and Related Systems Related information systems A DBMS can support several related information systems that provide input to, and require specific data from, the DBMS No human intervention is required for two-way communication

DBMS Components Data Manipulation Language A data manipulation language (DML) controls database operations, including storing, retrieving, updating, and deleting data Some database products also provide an easy-to-use graphical environment that enables users to control operations with menu-driven commands.

DBMS Components Schema The complete definition of a database, including descriptions of all fields, tables, and relationships, is called a schema You also can define one or more subschemas For example, specific users, systems, or locations might be permitted to create, retrieve, update, or delete data, depending on their needs and the company’s security policies

DBMS Components Physical Data Repository The data dictionary is transformed into a physical data repository, which also contains the schema and subschemas The physical repository might be centralized, or distributed at several locations ODBC – open database connectivity JDBC – Java database connectivity

Web-Based Database Design The following sections discuss the characteristics of Web-based design, Internet terminology, connecting a database to the Web, and data security on the Web

Web-Based Database Design Characteristics of Web-Based Design In a Web-based design, the Internet serves as the front end, or interface for the database management system. Internet technology provides enormous power and flexibility Web-based systems are popular because they offer ease of access, cost-effectiveness, and worldwide connectivity

Web-Based Database Design Internet Terminology Web browser Web page HTML (Hypertext Markup Language) Tags Web server Web site

Web-Based Database Design Internet Terminology Intranet Extranet Protocols Web-centric Clients Servers

Web-Based Database Design Connecting a Database to the Web Database must be connected to the Internet or intranet The database and the Internet speak two different languages Middleware Adobe ColdFusion

Web-Based Database Design Data Security Web-based data must be secure, yet easily accessible to authorized users To achieve this goal, well-designed systems provide security at three levels: the database itself, the Web server, and the telecommunication links that connect the components of the system

Data Design Terminology Definitions Entity Table or file Field Attribute Common field Record Tuple

Data Design Terminology Key Fields Primary key Combination key Composite key Concatenated key Multi-valued key

Data Design Terminology Key Fields Candidate key Nonkey field Foreign key Secondary key

Data Design Terminology Referential Integrity Validity checks can help avoid data input errors In a relational database, referential integrity means that a foreign key value cannot be entered in one table unless it matches an existing primary key in another table Orphan

Entity-Relationship Diagrams An entity is a person, place, thing, or event for which data is collected and maintained Entity-relationship diagram (ERD) An ERD provides an overall view of the system, and a blueprint for creating the physical data structures

Entity-Relationship Diagrams Drawing an ERD The first step is to list the entities that you identified during the fact-finding process and to consider the nature of the relationships that link them A popular method is to represent entities as rectangles and relationships as diamond shapes

Entity-Relationship Diagrams Types of Relationships Three types of relationships can exist between entities One-to-one relationship (1:1) One-to-many relationship (1:M) Many-to-many relationship (M:N) Associative entity

Entity-Relationship Diagrams Cardinality Cardinality notation Crow’s foot notation Unified Modeling Language (UML) Now that you understand database elements and their relationships, you can start designing tables

Normalization Normalization Table design Involves four stages: unnormalized design, first normal form, second normal form, and third normal form Most business-related databases must be designed in third normal form

Normalization Standard Notation Format Designing tables is easier if you use a standard notation format to show a table’s structure, fields, and primary key Example: NAME (FIELD 1, FIELD 2, FIELD 3)

Normalization Repeating Groups and Unnormalized Design Repeating group Often occur in manual documents prepared by users Unnormalized Enclose the repeating group of fields within a second set of parentheses

Normalization First Normal Form A table is in first normal form (1NF) if it does not contain a repeating group To convert, you must expand the table’s primary key to include the primary key of the repeating group

Normalization Second Normal Form To understand second normal form (2NF), you must understand the concept of functional dependence Field X is functionally dependent on field Y if the value of field X depends on the value of field Y

Normalization Second Normal Form A standard process exists for converting a table from 1NF to 2NF First, create and name a separate table for each field in the existing primary key Next, create a new table for each possible combination of the original primary key fields Finally, study the three tables and place each field with its appropriate primary key

Normalization Second Normal Form Four kinds of problems are found with 1NF description that do not exist with 2NF Consider the work necessary to change a particular product’s description 1NF tables can contain inconsistent data Adding a new product is a problem Deleting a product is a problem

Normalization Third Normal Form 3NF design avoids redundancy and data integrity problems that still can exist in 2NF designs A table design is in third normal form (3NF) if it is in 2NF and if no nonkey field is dependent on another nonkey field

Normalization Third Normal Form To convert the table to 3NF, you must remove all fields from the 2NF table that depend on another nonkey field and place them in a new table that uses the nonkey field as a primary key

Normalization A Normalization Example To show the normalization process, consider the familiar situation in Figure 9-27 which might depict several entities in a school advising system: ADVISOR, COURSE, and STUDENT

Using Codes During System Design Overview of Codes A code is a set of letters or numbers that represents a data item. Codes can be used to simplify output, input, and data formats. Because codes often are used to represent data, you encounter them constantly in your everyday life They save storage space and costs, reduce data transmission time, and decrease data entry time Can reduce data input errors

Using Codes During System Design Types of Codes [1] Sequence codes Numbers/letters assigned in a specific order E.g. UiTM student matric number [2] Block sequence codes Block sequence codes use blocks of numbers for different classifications. E.g. course codes 1xx – 3xx : diploma courses 4xx – 6xx : bachelor courses 7xx – 8xx : master courses

Using Codes During System Design Types of Codes [3] Alphabetic codes [a] Category codes – identify related items using numbers/letters E.g. ITS – system science courses, ITT – data comm. & networking courses, ITC – comp. science courses, ACC – accounting courses [b] Abbreviation codes – mnemonic codes/abbreviations E.g MY = Malaysia, SG = Singapore, NZ = New Zealand

Using Codes During System Design Types of codes [4] Significant digit codes - Distinguish items by using a series of subgroups of digits E.g. Classroom number in UiTM Pahang: J1-01, J1-02, A1- 01, A2-01 [5] Derivation codes - Combine data from different item attributes/characteristics to build the code E.g. Magazine release num: 201109.Vol.18 (Vol. 18, Released on September 2011) Cipher codes Action codes

Using Codes During System Design Types of codes [6] Cipher codes: use a keyword to encode a number E.g. E.g. IASETTO = 1453770 [7] Action codes - Indicate action to be executed associated with item E.g. X – exit program, F – File menu

Using Codes During System Design Developing a Code Keep codes concise Allow for expansion Keep codes stable Make codes unique Use sortable codes

Using Codes During System Design Developing a Code Avoid confusing codes Make codes meaningful Use a code for a single purpose Keep codes consistent

Steps in Database Design Create the initial ERD Assign all data elements to entities Create 3NF designs for all tables Verify all data dictionary entries After creating your final ERD and normalized table designs, you can transform them into a database

Database Models Relational Databases The relational model was introduced during the 1970s and became popular because it was flexible and powerful Because all the tables are linked, a user can request data that meets specific conditions New entities and attributes can be added at any time without restructuring the entire database

Database Models Object-Oriented Databases Many systems developers are using object-oriented database (OODB) design as a natural extension of the object-oriented analysis process Object Management Group (OMG) Each object has a unique object identifier

Data Storage and Access Data storage and access involve strategic business tools Strategic tools for data storage and access Data warehouse – dimensions Data mart

Data Storage and Access Strategic tools for data storage and access Data Mining Increase average pages viewed per session. Increase number of referred customers Reduce clicks to close Increase checkouts per visit Increase average profit per checkout Clickstream storage – market basket analysis

Data Storage and Access Logical and Physical Storage Logical storage Characters Date element or data item Logical record Physical storage Physical record or block Buffer Blocking factor

Data Storage and Access Data Coding and Storage Binary digits Bit Byte EBCDIC, ASCII, and Binary EBCDIC and ASCII

Data Storage and Access Data Coding and Storage EBCDIC, ASCII, and Binary Binary storage format Integer format Long integer format Unicode

Data Storage and Access Data Coding and Storage Storing dates Y2K Issue Most date formats now are based on the model established by the International Organization for Standardization (ISO) Absolute date

Data Control File and database control must include all measures necessary to ensure that data storage is correct, complete, and secure A well-designed DBMS must provide built-in control and security features, including subschemas, passwords, encryption, audit trail files, and backup and recovery procedures to maintain data

Data Control User ID Password Permissions Encryption Backup Recovery procedures Audit log files Audit fields

Chapter Summary Files and tables contain data about people, places, things, or events that affect the information system DBMS designs are more powerful and flexible than traditional file-oriented systems 49

Chapter Summary An entity-relationship (ERD) is a graphic representation of all system entities and the relationships among them A code is a set of letters or numbers used to represent data in a system The most common database models are relational and object-oriented 49

Chapter Summary Logical storage is information seen through a user’s eyes, regardless of how or where that information actually is organized or stored Physical storage is hardware-related and involves reading and writing blocks of binary data to physical media File and database control measures include limiting access to the data, data encryption, backup/recovery procedures, audit-trail files, and internal audit fields 49