Chapter 8knreddycse.weebly.com/uploads/5/7/2/0/57207825/imdb-chapter08.pdf · Systems Development Life Cycle (SDLC) •That, within the information system, the most successful databases

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Chapter 8

Database Design

Database Systems:Design, Implementation, and Management,

Sixth Edition, Rob and Coronel

Database Systems: Design, Implementation, & Management, 6th Edition, Rob & Coronel

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In this chapter, you will learn:•That successful database design must reflect

the information system of which the database isa part

•That successful information systems aredeveloped within a framework known as theSystems Development Life Cycle (SDLC)

•That, within the information system, the mostsuccessful databases are subject to frequentevaluation and revision within a frameworkknown as the Database Life Cycle (DBLC)


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In this chapter, you will learn (continued):

•How to conduct evaluation and revision withinthe SDLC and DBLC frameworks

•What database design strategies exist: top-down vs. bottom-up design, and centralizedvs. decentralized design


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Changing Data into Information

•Information

–Data processed and presented in ameaningful form

–Can be as simple as tabulating the data,thereby making certain data patterns moreobvious

•Transformation

–Any process that changes data intoinformation


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A Simple Cross-Classification Table:Transforming Data into Information


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The Information System•Provides for data collection, storage, and

retrieval•Composed of people, hardware, software,

database(s), application programs, andprocedures

•Systems analysis–Process that establishes need for and extent

of an information system

•Systems development–Process of creating an information system


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Applications

•Transform data into information that forms thebasis for decision making

•Usually produce–Formal report–Tabulations–Graphic displays

•Composed of two parts–Data–Code by which the data are transformed into

information


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Generating Informationfor Decision Making


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Information System•Performance depends on triad of factors:

–Database design and implementation–Application design and implementation–Administrative procedures

•Database development–Process of database design and

implementation–Primary objective is to create complete,

normalized, nonredundant (to the extentpossible), and fully integrated conceptual,logical, and physical database models


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The Systems Development Life Cycle(SDLC)

•Traces history (life cycle) of an informationsystem

•Provides “big picture”within which databasedesign and application development can bemapped out and evaluated


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The Systems Development Life Cycle(SDLC) (continued)

• Divided into five phases

1. Planning

2. Analysis

3. Detailed systems design

4. Implementation

5. Maintenance

• Iterative rather than sequential process


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Planning•Yields general overview of the company and

its objectives

•Initial assessment made of information-flow-and-extent requirements

•Must begin to study and evaluate alternatesolutions

–Technical aspects of hardware and softwarerequirements

–System cost


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The Systems Development Life Cycle(SDLC)


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Analysis

•Problems defined during the planning phaseare examined in greater detail during analysis

•A thorough audit of user requirements

•Existing hardware and software systems arestudied

•Goal is better understanding of system’sfunctional areas, actual and potentialproblems, and opportunities


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Logical Systems Design

•Must specify appropriate conceptual datamodel, inputs, processes, and expectedoutput requirements

•Might use tools such as data flow diagrams(DFD), hierarchical input process output(HIPO) diagrams, or entity relationship (ER)diagrams

•Yields functional descriptions of system’scomponents (modules) for each processwithin database environment


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Detailed Systems Design

•Designer completes design of system’sprocesses

•Includes all necessary technicalspecifications

•Steps are laid out for conversion from old tonew system

•Training principles and methodologies arealso planned


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Implementation

•Hardware, DBMS software, and applicationprograms are installed, and database designis implemented

•Cycle of coding, testing, and debuggingcontinues until database is ready to bedelivered

•Database is created and system iscustomized by creation of tables and views,and user authorizations


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Maintenance

•Three types:–Corrective maintenance in response to

systems errors–Adaptive maintenance due to changes in the

business environment–Perfective maintenance to enhance the

system•Computer-assisted systems engineering

–Make it possible to produce better systems withinreasonable amount of time and at a reasonablecost


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The Database Life Cycle (DBLC)


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The Database Initial Study

•Overall purpose:

–Analyze the company situation

–Define problems and constraints

–Define objectives

–Define scope and boundaries

•Interactive and iterative processes required tocomplete the first phase of the DBLCsuccessfully


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Summary of Activities in the DatabaseInitial Study


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Analyze the Company Situation

•Analysis–“To break up any whole into its parts so as to

find out their nature, function, and so on”•Company situation

–General conditions in which a companyoperates, its organizational structure, and itsmission

•Analyze the company situation–Discover what the company’s operational

components are, how they function, and howthey interact


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Define Problems and Constraints

•Managerial view of company’s operation isoften different from that of end users

•Designer must continue to carefully probe togenerate additional information that will helpdefine problems within larger framework ofcompany operations

•Finding precise answers is important

•Defining problems does not always lead tothe perfect solution


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Define Objectives•Designer must ensure that database system

objectives correspond to those envisioned byend user(s)

•Designer must begin to address the followingquestions:–What is the proposed system’s initial objective?–Will the system interface with other existing or

future systems in the company?–Will the system share data with other systems

or users?


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Define Scope and Boundaries•Scope

–Defines extent of design according tooperational requirements

–Helps define required data structures, type andnumber of entities, and physical size of thedatabase

•Boundaries–Limits external to the system–Often imposed by existing hardware and

software


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Database Design

•Necessary to concentrate on the data

•Characteristics required to build databasemodel

•Two views of data within system:

–Business view of data as information source

–Designer’s view of data structure, its access,and the activities required to transform thedata into information


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Two Views of Data:Business Manager and Designer


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Database Design (continued)•Loosely related to analysis and design of larger

system•Systems analysts or systems programmers are

in charge of designing other systemcomponents–Their activities create procedures that will help

transform data within the database into usefulinformation

•Does not constitute a sequential process–Iterative process that provides continuous

feedback designed to trace previous steps


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Procedure Flow in the Database Design


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Conceptual Design

•Data modeling used to create an abstractdatabase structure that represents real-worldobjects in the most realistic way possible

•Must embody a clear understanding of thebusiness and its functional areas

•Ensure that all data needed are in the model,and that all data in the model are needed

•Requires four steps


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Data Analysis and Requirements

•First step is to discover data elementcharacteristics

–Obtains characteristics from different sources

•Must take into account business rules

–Derived from description of operations

•Document that provides precise, detailed, up-to-date, and thoroughly reviewed description ofactivities that define an organization’s operatingenvironment


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Entity Relationship (ER) Modelingand Normalization

•Designer must communicate and enforceappropriate standards to be used in thedocumentation of design

–Use of diagrams and symbols

–Documentation writing style

–Layout

–Other conventions to be followed duringdocumentation


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Developing the Conceptual ModelUsing ER Diagrams


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A Composite Entity


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Data Redundancies in the VIDEO Table


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ER Modeling Is an Iterative ProcessBased on Many Activities


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Conceptual Design Toolsand Information Sources


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Data Dictionary

•Defines all objects (entities, attributes,relations, views, and so on)

•Used in tandem with the normalizationprocess to help eliminate data anomalies andredundancy problems


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Data Model Verification•Model must be verified against proposed system

processes to corroborate that intended processescan be supported by database model

•Revision of original design starts with a carefulreevaluation of entities, followed by a detailedexamination of attributes that describe theseentities

•Define design’s major components as modules:

–An information system component that handles aspecific function


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The ER Model Verification Process


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Iterative ER Model Verification Process


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Verification Process

•Select the central (most important) entity

–Defined in terms of its participation in most ofthe model’s relationships

•Identify the module or subsystem to which thecentral entity belongs and define boundariesand scope

•Place central entity within the module’sframework


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DBMS Software Selection

•Critical to the information system’s smoothoperation

•Advantages and disadvantages should becarefully studied


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Logical Design

•Used to translate conceptual design intointernal model for a selected databasemanagement system

•Logical design is software-dependent

•Requires that all objects in the model bemapped to specific constructs used byselected database software


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A Simple Conceptual Model


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Sample Layout for the COURSE Table


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Physical Design

•Process of selecting data storage and dataaccess characteristics of the database

•Storage characteristics are a function ofdevice types supported by the hardware, typeof data access methods supported by system,and DBMS

•Particularly important in the older hierarchicaland network models

•Becomes more complex when data aredistributed at different locations


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Implementation and Loading

•New database implementation requires thecreation of special storage-related constructsto house the end-user tables


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Physical Organization of a DB2 DatabaseEnvironment


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Performance

•One of the most important factors in certaindatabase implementations

•Not all DBMSs have performance-monitoringand fine-tuning tools embedded in theirsoftware

•There is no standard measurement fordatabase performance

•Not only (nor even main) factor


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Security

•Data must be protected from access byunauthorized users

•Must provide for the following:–Physical security

–Password security

–Access rights

–Audit trails

–Data encryption

–Diskless workstations


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Backup and Recovery

•Database can be subject to data loss throughunintended data deletion and power outages

•Data backup and recovery procedures

–Create a safety valve

–Allow database administrator to ensureavailability of consistent data


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Integrity

•Enforced through proper use of primary andforeign key rules


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Company Standards

•May partially define database standards

•Database administrator must implement andenforce such standards


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Concurrency Control

•Feature that allows simultaneous access to adatabase while preserving data integrity

•Failure to maintain can quickly destroy adatabase’s effectiveness


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The Need for Concurrency Control


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Testing and Evaluation•Occurs in parallel with applications

programming•Database tools used to prototype applications•If implementation fails to meet some of the

system’s evaluation criteria–Fine-tune specific system and DBMS

configuration parameters–Modify the physical design–Modify the logical design–Upgrade or change the DBMS software and/or

the hardware platform


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Operation

•Once the database has passed theevaluation stage, it is considered operational

•Beginning of the operational phase starts theprocess of system evolution


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Maintenance and Evolution

•Required periodic maintenance:–Preventive maintenance–Corrective maintenance–Adaptive maintenance

•Assignment of access permissions and theirmaintenance for new and old users

•Generation of database access statistics•Periodic security audits•Periodic system-usage summaries


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Parallel Activities in theDBLC and the SDLC


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A Special Note aboutDatabase Design Strategies

•Two classical approaches to database design:

–Top-down design

•Identifies data sets

•Defines data elements for each of those sets

–Bottom-up design

•Identifies data elements (items)

•Groups them together in data sets


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Top-Down vs. Bottom-Up DesignSequencing


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Centralized vs. Decentralized Design•Database design may be based on two very

different design philosophies:

–Centralized design

•Productive when the data component iscomposed of a relatively small number ofobjects and procedures

–Decentralized design

•Used when the data component of system hasconsiderable number of entities and complexrelations on which very complex operations areperformed


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Centralized Design


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Decentralized Design


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Aggregation Process

•Requires designer to create a single model inwhich various aggregation problems must beaddressed:

–Synonyms and homonyms

–Entity and entity subtypes

–Conflicting object definitions


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Summary of Aggregation Problems


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Summary

•Transformation from data to information isproduced when programming code operateson the data, thus producing applications

•Information system is designed to facilitatetransformation of data into information and tomanage both data and information

•SDLC traces the history (life cycle) of anapplication within the information system


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Summary (continued)

•DBLC describes the history of the databasewithin the information system

•Database design and implementation processmoves through a series of well-definedstages

•Conceptual portion of the design may besubject to several variations, based on twodesign philosophies

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Chapter 8knreddycse.weebly.com/uploads/5/7/2/0/57207825/imdb-chapter08.pdf · Systems Development Life Cycle (SDLC) •That, within the information system, the most successful databases