Preparing to Automate Data Management

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Chapter 1

“You can use all the quantitative data you can get, but you stillhave to distrust it and use your own intelligence and judgment.” — Alvin Toffler

Chapter Introduction• Discovery phase includes

– Gathering all existing data – Researching missing and incomplete data– Talking with users about data output needs

• Subsequent steps in process include– Putting data into groups called tables– Identifying unique values for each record in those

tables – Designing database to produce desired output

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Database Design Process: The Discovery Phase

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Level 1 Objectives: Examining Existing and Missing Sources of Data• Discover and evaluate sources of existing

business data• Research sources of missing or incomplete data• Assign data to tables and use field types and sizes

to define data

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Discovering and Evaluating Sources of Existing Data• Identify information that organization needs to

manage and organize• Might begin to see patterns that indicate how to

organize data• Database management system (DBMS)

– Includes:• Oracle • ColdFusion• Microsoft Access• MySQL

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Discovering and Evaluating Sources of Existing Data (cont’d)• Data duplication

– Undesirable • Additional space required in database to store extra

records• Leads to inconsistent and inaccurate data

• Data redundancy– Same data repeated for different records

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Researching Sources of Missing Data• Part of discovery phase• Must ask right questions of right people to get

right answers

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Assimilating the Available Information and Planning the Database• First step in database design

– Determine best way to organize data into logical groups of fields

• Field – Single characteristic of entity– Also called column

• Record– Values in each field in table– Also called row

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Assimilating the Available Information and Planning the Database (continued)• Table

– Collection of fields that describe one entity– Also called entity or relation

• Database– Collection of one or more tables

• Relational database– Contains related tables through fields that contain

identical data

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Evaluating Field Values and Assigning Appropriate Data Types• Data type

– Determines how to store data in field• DBMSs use different names for some data types• How do you determine which data type to assign

each field? – Depends on what function you want to derive from

data– Each data type has different properties

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Common Data Types and Their Descriptions

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The Text and Memo Data Types• Text data type

– Letters and numbers– Not used in calculations or formulas– Stores maximum of 255 characters– Default for all fields created in access database

• Memo data type– Store long passages of text– Displays only 64,000 characters

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The Number Data Type• Stores both positive and negative numbers • Contains up to 15 digits• Use for values used in calculations

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The Currency Data Type• Includes two decimal places and displays values

with dollar sign• Use for monetary values

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The Date/Time Data Type• Display values in format mm/dd/yyyy

– Can also include time in different formats• Used in calculations if necessary

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The AutoNumber Data Type• Unique to Access• Number automatically generated by access • Produces unique values for each record• Useful to distinguish two records that share

identical information• Produces values of up to nine digits

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The Yes/No Data Type• Assigned to fields requiring

– Yes/no– True/false– On/off

• Takes up one character of storage space• Make data entry easy

– Check box

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The OLE Object Data Type• Used to identify files created in another program

- Then linked or embedded in database• Abbreviation for object linking and embedding

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The Hyperlink Data Type• Assigned to fields that contain hyperlinks to

– Web pages– E-mail addresses– Files that open in

• Web browser• E-mail client• Another application

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The Lookup Wizard Data Type• Creates fields to look up data in

– Another table– Or list of values created for field

• Makes data entry easy • Ensures that valid data entered into field

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The Attachment Data Type• New to Access 2007• Lets you store one or more files for each record

in the database

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Selecting the Correct Data Type• Helps store correct data in correct format while

using least amount of space• Eases data entry and interactivity with data • Choosing certain data types results in user-

friendly interactive features– Drop-down menus – Check boxes– Hyperlinks

• Correctly manipulate data

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Assigning the Correct Field Size for Text Fields• Important to consider field size when assigning

data types– Minimize space reserved for each record by assigning

smallest data type that will store data• Be conservative when assigning field sizes

– But not too conservative

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Assigning the Correct Field Size for Number Fields

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Dividing the Existing and Missing Data into Tables• Tables

– Single most important component of database– Most databases contain

• Multiple tables • Hundreds or even thousands of records

• Primary key – One field that creates unique value in each record – Used to identify each record in table– May be a combination of fields

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Database Design Process: Planning the Tables

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Naming Conventions• Database tables must

– Have unique names– Follow established naming conventions

• General rules for naming objects– Object names cannot exceed 64 characters– Object names cannot include period, exclamation

point, accent grave, or brackets– Object names should not include spaces– Most developers capitalize first letter of each word

when table name includes two words

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Leszynski/Reddick Naming Conventions for Database Objects

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Level 1 Summary• Discovery phase• Identify existing and missing data• Determine tables

– Determine data types• Follow naming conventions

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Level 2 Objectives:Understanding and Creating Table Relationships• Understand relational database objects and

concepts• Create table relationships• Understand referential integrity

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Understanding Relational Database Objects• Users can view data in tables by:

– Opening table – Creating other objects

• Four main objects in database – Tables– Queries– Forms– Reports

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Tables• Data in relational database stored in one or more

tables• View data in table

– Open it and scroll through records• Most of the time, three other main database

objects used to display data normally

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Queries• Query

– Question asked about data stored in database• Query results

– Look similar to table– Fields displayed in columns – Records displayed in rows

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Queries (continued)• Select query

– Most commonly used query– Data selected from table on which query based

• Action query– Performs action on table– Select specific records in table and update them

• Crosstab query – Performs calculations on values in field and displays

results in datasheet

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Forms• Used to view add delete, update and print records in

database• Based on table or query• Interface more attractive than table datasheet• Customize form’s appearance with instructions and

command buttons• Switchboard

– Form displayed when database opened– Provides controlled method for users to open objects in

database

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Form Based on a Table

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Reports• Formatted presentation of data from table or

query • Created as printout or to be viewed on screen• Data displayed by report usually based on query• Dynamic

– Reflect latest data from object• Cannot be used to modify data

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Accounts Receivable Report

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Other Database Objects• Macro

– Set of instructions – Automate certain database tasks– Usually automates simple tasks

• Module – Contains instructions to automate database task– Written in Visual Basic for Applications (VBA)– Performs more sophisticated actions than macro

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Understanding Relational Database Concepts• Flat file database

– Simple database – Contains single table of information

• Relational database– Contains multiple tables to store related information

• Common field – Field that appears in two or more tables and contains

identical data to relate tables– Primary key in first table– Foreign key in second table

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Creating Table Relationships• Take advantage of interrelated objects• Goal in good database design

– Create separate tables for each entity– Ensure each table has primary key– Use common field to relate tables

• Relate two (or more) tables– Query them as though they are one big table

• Join – Specifies relationship between tables and properties

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One-to-Many Relationships• Abbreviated as 1:M• One record in first table matches zero one or

many records in related table• Primary table

– One side• Related table

– Many side

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One-to-Many Relationship Between Customers and Prescriptions

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One-to-One Relationships• Abbreviated as 1:1• Exists when each record in one table matches

exactly one record in related table

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One-to-One Relationship Between Physical and Billing Addresses

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Many-to-Many Relationships• Abbreviated as M:N• Each record in first table matches many records

in second table• Each record in second table matches many

records in first table• Junction table

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Many-to-Many Relationship Between Employees and Classes

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Understanding Referential Integrity• Null value

– Field does not contain any value

• Entity integrity– Guarantee that there are no duplicate records in table– Each record unique– No primary key field contains null values

• Referential integrity – If foreign key in one table matches primary key in second table – Values in foreign key must match values in primary key

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Understanding Referential Integrity (continued)• When database does not enforce referential

integrity – Problems occur that lead to inaccurate and

inconsistent data• Orphaned

– No longer match between primary key in primary table and foreign keys in related table

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Referential Integrity Errors

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Overriding Referential Integrity• Might want to override referential integrity

– Intentionally change primary key – Delete parent record

• Cascade updates– Change primary key value so that DBMS

automatically updates appropriate foreign key values in related table

• Cascade deletes

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Level 2 Summary• Main database objects:

– Table– Query– Form– Report

• Relationship types:– One-to-many– One-to-one– Many-to-many

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Level 3 Objectives: Identifying and Eliminating Database Anomalies by Normalizing Data• Learn the techniques for normalizing data• Evaluate fields that are used as keys• Test the database design

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Normalizing the Tables in the Database• Normalization

– Design process– Goals

• Reduces space required to store data by eliminating duplicate data in database

• Reduces inconsistent data in database by storing data only once

• Reduces chance of deletion update and insertion anomalies

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Normalizing the Tables in the Database (continued)• Deletion anomaly

– User deletes data from database – Unintentionally deletes only occurrence of data in database

• Update anomaly – Due to redundant data in database– User fails to update some records or updates records

erroneously

• Insertion anomaly – User cannot add data to database unless preceded by entry of

other data

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Normalizing the Tables in the Database (continued)• Functional dependency

– Column in table considered functionally dependent on another column

• If each value in second column associated with exactly one value in first column

• Partial dependency – Field dependent on only part of primary key

• Composite primary key– Primary key uses two or more fields to create unique

records in table

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Normalizing the Tables in the Database (continued)• Determinant

– Field or collection of fields whose value determines value in another field

– Inverse of dependency• Natural key

– Primary key that details obvious and innate trait of record

• Artificial key– Field whose sole purpose is to create primary key– Usually visible to users

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Normalizing the Tables in the Database (continued)• Surrogate key

– Computer-generated primary key – Usually invisible to users

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First Normal Form• Repeating group

– Field contains more than one value• First normal form

– 1NF– Does not contain any repeating groups

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Second Normal Form• 2NF• Table must be in 1NF • Must not contain any partial dependencies on

composite primary key• Tables in 1NF and contain primary key with only

one field – Automatically in 2NF

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Third Normal Form• 3NF• Only determinants must be candidate keys• Candidate key

– Field or collection of fields that could function as primary key but was not chosen to do so

• Transitive dependency – Occurs between two nonkey fields both dependent

on third field• Tables in 3NF should not have transitive

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Level 3 Summary• Normal forms

– First (1NF)– Second (2NF)– Third (3NF)

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Chapter Summary• Discovery:

– Identify existing and missing data– Organize data into tables– Determine data types for each field

• Table relationships– Established through common fields– Types

• 1:M• 1:1• M:N

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Chapter Summary (continued)• Normalization

– Reduces duplication and inconsistency– Forms:

• 1NF• 2NF• 3NF

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