Systems analysis and design methods 7th whitten and benley chapter 11

Database Design Introduction  How does a relational database implement entities, attributes, and relationships from a logical data model?. Database Design Information System System Info

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Database Design

Introduction

 What are the similarities and differences between conventional files and modern, relational databases?

 What are of fields, records, files, and databases? What are some examples of each?

 What is a modern data architecture that includes files, operational databases, data warehouses, personal databases, and work group databases?

 What are the similarities and differences between the roles of

systems analyst, data administrator, and database administrators as they relate to databases?

 What is the architecture of a database management system?

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Database Design

Introduction

 How does a relational database implement entities, attributes, and relationships from a logical data model?

 How do you normalize a logical data model to remove impurities that can make a database unstable, inflexible, and non-scaleable?

 How do you transform a logical data model into a physical,

relational database schema?

 How do you generate SQL code to create the database structures in

a schema?

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• The key word is interrelated

• The records in each file must allow for relationships (think of them

as ‘pointers’) to the records in other files

 In the file environment, data storage is built around the

applications that will use the files

 In the database environment, applications will be built around the integrated database

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Database Design

Information System

System

Database (consolidated &

integrated data from files) File

File

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 Historically, another advantage of conventional files has been processing speed

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Database Design

Conventional Files Versus the

Database

 As legacy file-based systems and applications become candidates for reengineering, the trend is overwhelmingly in favor of

replacing file-based systems and applications with database

systems and applications

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 Databases allow the use of the data in ways not originally

specified by the end-users - data independence

 The database scope can even be extended without impacting

existing programs that use it

• New fields and record types can be added to the database without affecting current programs.

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required

programmers must learn how to use the DBMS

and database specialists must adhere to rigorous design principles

increased vulnerability inherent in the use of shared data.

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Database Design

Conventional Files Versus the

Database

 To fully exploit the advantages of database technology, a database must be carefully designed

 The end product is called a database schema, a technical blueprint

of the database

 Database design translates the data models that were developed for the system users during the definition phase, into data structures supported by the chosen database technology

 Subsequent to database design, system builders will construct

those data structures using the language and tools of the chosen database technology

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FOCUS ON SYSTEM PROCESSES

FOCUS ON SYSTEM INTERFACES

Existing Applications and Technology

Existing Interfaces and Technology

Existing Networks and Technology

FOCUS ON SYSTEM GEOGRAPHY

Implementation Phase (translate technical design into code)

Design Phase (translate business requirements into a technical design)

Definition Phase (establish and prioritize business system requirements)

Study Phase (establish system improvement objectives)

Survey Phase (establish scope and project plan)

ORDER order-no order-date products-ordered

Customers order zero,

one, or more products

Products may be ordered

by zero, one, or more

CREATE TABLE CUSTOMER

(customer_no CHAR(10) NOT NULL

customer_name CHAR(32) NOT NULL

customer _rating CHAR(1) NOT NULL

balance_due DECIMAL(5,2)

CREATE INDEX cust_no_idx on CUSTOMER

CREATE INDEX cust_rt_idx on CUSTOMER

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Database Design

Database Concepts for the Systems

Analyst

 Fields are common to both files and databases

 A field is the implementation of a data attribute

• Fields are the smallest unit of meaningful data to be stored in a file

or database.

 There are four types of fields that can be stored: primary keys,

secondary keys, foreign keys, and descriptive fields.

one record in a file

• A single file in a database may only have one primary key, but it

may have several secondary keys.

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 There are four types of fields that can be stored: primary keys,

secondary keys, foreign keys, and descriptive fields (continued)

database

• Foreign keys are how the database ‘links’ the records of one type

to those of another type.

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Database Design

Analyst

fixed-length or variable-fixed-length records

meaning that each record instance has the same fields, same number of fields, and same logical size

same file to have different lengths

length records

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 When a computer program ‘reads’ a record from a database, it

actually retrieves a group or block of records at a time

 This approach minimizes the number of actual disk accesses

 A blocking factor is the number of logical records included in

a single read or write operation (from the computer’s

perspective) A block is sometimes called a physical record.

 Today, the blocking factor is usually determined and optimized

by the chosen database technology, but a qualified database expert may be allowed to fine tune that blocking factor for performance

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Database Design

Analyst

usually called a table.

permanent

system indefinitely

the individual records are retained indefinitely

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Database Design

Analyst

 Some of the types of files and tables include: (continued)

business events

• The data describing these events normally has a limited useful lifetime

• In information systems, transaction records are frequently retained

on-line for some period of time

• Subsequent to their useful lifetime, they are archived off-line.

data for easy retrieval and review without the overhead of generating the document

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re-Database Design

Analyst

records that have been deleted from on-line storage

• Records are rarely deleted; they are merely moved from on-line storage to off-line storage

• Archival requirements are dictated by government regulation and the need for subsequent audit or analysis.

shared by applications to maintain consistency and improve performance

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Database Design

Analyst

especially master and transaction files

• They are used in conjunction with archive files to recover ``lost’’ data

• Audit trails are typically built into better database technologies.

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 Out of necessity, database technology was created so an

organization could maintain and use its data as an integrated whole instead of as separate data files

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 A business’ data architecture is comprised of the files and

databases that store all of the organization’s data, the file and database technology used to store the data, and the organization structure set up to manage the data resource

day-to-day operations and business transaction processing for major information systems

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production databases and conventional files

– Fourth-generation programming languages, query tools, and

decision support tools are then used to generate reports and analyses off these data warehouses.

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• These databases may contain unique data, or they may import data

from conventional files, operational databases, and/or data warehouses

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• A data administrator is responsible for the data planning,

definition, architecture, and management.

– One or more database administrators are responsible for the

database technology, database design and construction, security, backup and recovery, and performance tuning.

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Database Design

A legacy file-based information system (built in-house)

File

(built in-house)

Information System (built in-house)

Operational Database File

File

Information System (built in-house)

A legacy file-based information system (purchased)

File File File

Information System (purchased)

Operational Database

Data Warehouse

End-User Tools

End-User Applications

Personal DB

Work-Group Database

Users and Programmers

Users

End-User Work Group

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including the database engine, database management utilities, database CASE tools for analysis and design, and database application development tools.

management system

software available from computer vendors that is used to create, access, control, and manage the database The core of the DBMS is

often called its database engine The engine responds to specific

commands to create database structures, and then to create, read, update, and delete records in the database.

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record types, and relationships that exist between record types.

 These structures are defined to the database management system using its data definition language

physically establish those record types, fields, and structural relationships Additionally, the DDL defines views of the database Views restrict the portion of a database that may be used or

accessed by different users and programs DDLs record the definitions in a permanent data repository.

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Database Design

Database Management System (DBMS)

Data Definition Language DDL

Data Manipulation Language DML

Proprietary Data Manipulation Language and/or Report Writers

Host-based Transaction Processing Monitor (optional)

Internal

TP Monitor (opt)

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helps database specialists track metadata – the data about the

data –such as record and field definitions, synonyms, data relationships, validation rules, help messages, and so forth

manipulation language to access and use the database in applications

update, and delete records in the database, and to navigate between different records and types of records The DBMS and DML hide the details concerning how records are organized and allocated to the disk.

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 Some DBMSs include a transaction processing monitor (or

TP monitor) that manages on-line accesses to the database, and

ensures that transactions that impact multiple tables are fully processed as a single unit

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can be classified according to the way they structure records

hierarchies or networks implemented with indexes and linked lists.

‘related’ to one another via foreign keys.

relations

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Quantity Ordered

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Database Design

Analyst

 Relational Database Management Systems:

 Both the DDL and DML of most relational databases is called

SQL (which stands for Structured Query Language)

• SQL supports not only queries, but complete database creation and maintenance

• A fundamental characteristic of relational SQL is that commands return ‘a set’ of records, not necessarily just a single record (as in non-relational database and file technology).

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 Relational Database Management Systems:

 High-end relational databases also extend the SQL language to support triggers and stored procedures

automatically invoked by a updates to another table

be called from an application program.

 Both triggers and stored procedures are reusable because they are stored with the tables themselves

• This eliminates the need for application programmers to create the

equivalent logic within each application that use the tables.

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Database Design

Data Analysis for Database Design

 A good data model is simple

 As a general rule, the data attributes that describe an entity should describe only that entity

 A good data model is essentially non-redundant

 This means that each data attribute, other than foreign keys, describes at most one entity

 A good data model should be flexible and adaptable to future

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implementation as a simple, non-redundant, flexible, and adaptable database The specific technique is called

normalization.

that they are grouped together to form stable, flexible, and adaptive entities.

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 An entity is in first normal form (1NF) if there are no

attributes that can have more than one value for a single instance of the entity

 An entity is in second normal form (2NF) if it is already in

1NF, and if the values of all non-primary key attributes are dependent on the full primary key – not just part of it

 An entity is in third normal form (3NF) if it is already in

2NF, and if the values of its non-primary key attributes are not dependent on any other non-primary key attributes

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Database Design

Data Analysis for Database Design

 First Normal Form:

 The first step in data analysis is to place each entity into 1NF

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Database Design

MEMBER ORDER -Key Data - Order-Number (PK)

-Non-Key Data - Order-Creation-Date

Order-Automatic-Fill-Date Member Number (FK1)

Member-Name Member-Address

Shipping-Address Shipping Instructions Club-Name (FK2) Promotion-Number (FK2)

Title-Cover Catalog-Description Copyright-Date Entertainment-Category Credit-Value

Director Video-Category Video-Sub-Category Closed-Captioned Language Running-Time

GAME TITLE -Key Data - Product-Number (PK1) Universal-Product-Code (PK1) -Non-Key Data - Manufacturer

Game-Category Game-Sub-Category Game-Platform Game-Media-Type Number-of-Players Parent-Advisory-Code

is a

MEMBER -Key Data - Member-Number (PK1)

-Non-Key Data - Member-Name

Member-Status Member-Street-Address Member-Daytime-Phone-Number Date-of-Last-Order Member-Balance-Due Member-Bonus-Balance-Available Member-Credit-Card-Information

-Non-Key Data - Club-Description

enrolls in

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