das - database design (erd) .pdf

Database Design: Logical & Physical ModelingDatabase Accounting Systems

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Systems Development Life Cycle

Planning RequirementsAnalysis Design CodingImplemen-

tation Operation

Logical ModelingPhysical Modeling

Classical Model

MSAccess

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Logical Design Tools

Flowchart Data Flow Diagram Entity-RelationshipDiagram

DatabaseOverall Schema

Maps the dataenvironment ina process-oriented manner

Maps the dataenvironment in a relationship-oriented manner

Maps the dataenvironment ina proceduralmanner

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Logical Modeling





Physical ModelingDesign of relational database tables


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Logical Modeling





Physical ModelingDesign of relational database tables


CodingCreate database in MSAccess

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Data Flow Diagram Flowchart Comparison Manual processing

DFD Flowchart

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Data Flow Diagram Flowchart Comparison Computer Processing Magnetic Tape

DFD Flowchart

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Data Flow Diagram Flowchart Comparison Computer Processing Magnetic Disk

DFD Flowchart

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ERD Modeling

Makes sure that the database captures and stores data about each business activity the company intends to plan, control or evaluate

It produces a database that is in third normal form (3NF)

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Entity Relationship Diagram

Entity - any class of objects about which data is collected.

Customer

OrderSale

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Attributes - properties or characteristics of an entity that are of interest

Invoice #

CustomerName

TelephoneNumber

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Relationship - the link between one or more entities describing how they are related

Pays for

Received by

Made to

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Cardinality - the number of occurrences of one entity that may be associated with a single occurrence of the other entity. Maximum Cardinality Minimum Cardinality

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Employee Is married to

Employee #

Address

Telephone #

Unary Relationship

Name1

1

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Entity Relationship DiagramBinary Relationship

Sales Pays for

Invoice #

CashCollectionsItem

Price $ Amount

CustomerName

Invoice #

1 N

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Office

Employee ComputerIs assigned to

Ternary Relationship

1

1

1

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1) Do not include attributes in ERD2) Use only binary relationships in ERD

2 SimplifyingAssumptions!!!

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Sample E-R Diagrams

SupervisorsEmployers

Departments

Part ofManages

Managed

By

Customer Orders Sales

Cash Receipts

Part of Part of

Players Teams LeaguePart of Part of

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Maximum Cardinality - the maximumnumber of occurrences of one entity that may be associated with a single occurrence of the other entity. One to One One to Many Many to One Many to Many

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Entity Relationship DiagramMaximum Cardinalities

One to One (1:1) Relationships

e.g. Cash Sale Each instance of a sale is linked to at most one instance of

a cash collections event Each instance of a cash collection is linked to at most one

instance of a sales event

Sales Pays for CashCollections1 1

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One to Many (1:N) Relationships

e.g. Installment Payments Each instance of a sale is linked to many instances of a

cash collection event Each instance of a cash collection is linked to at most one

instance of a sales event event

Sales Pays for CashCollections1 N


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Many to One (N:1) Relationships

e.g. Paying monthly store card in full Each instance of a sale is linked to at most one instance of

a cash collections event Each instance of a cash collection is linked to many

instances of a sales event

Sales Pays for CashCollectionsN 1


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Many to Many (N:N) Relationships

e.g. Paying monthly store card in part each month (balance forward method)

Each instance of a sale is linked to many instances of a cash collections event

Each instance of a cash collection is linked to many instances of a sales event

Sales Pays for CashCollectionsN N


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How do you know what the maximum cardinalities should be?

Companys business policies General business knowledge

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ERD MethodologyData Modeling Reading example

1. Identify the entities for the ERD using the:

REA model

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Resource Event Agent Model

Resource

Event

Agent

Things of economic value to an organization that it wants to collect data about, which includes: 1) Assets - cash, inventory, supplies, stores2) Intangibles (not on balance sheet) employee

services, manufacturing techniques3) Items not owned neighborhoods (in a real estate

database), delivery routes (used by a truckingcompany)

All organizations activities about which management wants to collect data - sales, cash collections, customer orders

Types of people an organization collects data about, people who participate in events - employee, vendor, customer

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2. Draw rectangles to represent each entity and arrange event entities in chronological order on page (start with events and then add related resources and agents)

CashCollections

Sales

Resource Event Agent

Cash

SalespersonInventory

Customer

Cashier


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3. Add diamonds to represent important relationships

CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto


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4. Specify maximum relationship cardinalities

CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto

N N N

NN

NN

N

N1

1

1

1

1


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5. Specify minimum relationship cardinalities

CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto


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Minimum Cardinality - the minimumnumber of occurrences of one entity that may be associated with a single occurrence of the other entity.

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How do you know what the minimum cardinalities should be? Companys business policies Knowledge of effective internal

controls

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Minimum Cardinalities and Internal Control

Internal controls:1) Safeguard the assets2) Ensure the accuracy & reliability of

the accounting data3) Ensure efficient operations4) Enforce managerial policies

Some of these controls can be built into thestructure of the database

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Minimum Cardinalities and Internal Control

For good Internal Control there are 3 types of minimum cardinalities:1) Event-Resource 2) Event-Agent3) Event-Event

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CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto


1 0

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Event-Resource Relationships

Every event involves the acquisition, use or disposal of some resource, but a resource may not be involved in any event

Each instance of inventory is linked to a minimum of zero sales events (ie. Unsold or slow-moving inventory - mana-gerial control)

Each instance of a sale is linked to a minimum of one inven-tory item (sale w/o inventory indicates a transaction error)

Inventory Line Item Sales1 0

Entity Relationship DiagramMinimum Cardinalities

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CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto


10

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Event-Agent Relationships

Ensures that all events are legitimate Each instance of a sale must be made by a minimum of one

salesperson (sale w/o salesperson indicates a transaction error)

Each salesperson is linked to a minimum of zero sales (ie. Person is not effective or was on vacation for the period, etc - managerial control.)

Sale Party to Salesperson0 1


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CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto


1

0

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Event-Event Relationships

Ensures that events are legitimate and occur in proper order Each instance of a sale is linked to a minimum of zero cash

collections (ie. uncollected A/R, overdue accounts, etc. -managerial control)

Each cash collection is linked to a minimum of one previous sale (cash collection without a previous sale indicates a transaction error)

Sales Pays for Cash Collection

1 0


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CashCollections

Sales


Cash


Customer

Cashier

Increases

Lineitems

Paysfor

Receivedby

Receivedfrom

Madeto

Partyto

1 0 0

01

00

0

01

1

1

1

1


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Summary of some ERD Rules

Relationships go through EVENTS; there are not Resource Agent relationships

Only one

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Physical Modeling

Once the ERD is finished you convert this diagram into relational database tables

Then apply Normalization rules and make sure the database is in desired normal form

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Physical ModelingERD Conversion

General Guidelines1) Create tables for each Entity and N:N relationship2) Primary key for entity table is a single numeric field;

Primary key for N:N relationship table are two fields3) Link the resulting tables

For tables in a 1:1 relationship, insert a foreign key in one ofthe two tables. In event-event relationships, put foreign key in later event table.

For tables in a 1:N relationship, put foreign key in table of entity participating many times in relationship

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Coding

1) Create and link tables in MSAccess2) Create forms for each event process3) Create forms for maintenance of each

agent and resource entity4) Create queries and reports for each

information process

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Effects of Databases on Accounting

Mechanics of storing and retrieving accounting information change

Journals and Ledgers are outputs of the system, not the core of the system

Less emphasis on double-entry bookkeeping Some internal controls are built into the

database structure

ENDDatabase Design: Logical &

Physical ModelingDatabase Accounting Systems

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Review of ERD Modeling andDatabase Design

Database Accounting SystemsActg/IDS 475

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ERD Modeling Approach

From the problem description determine what are the data elements to be captured in the database. These are fields within entities.

Determine what entities those fields will be contained in. If you only need one data element about something that is a field. If

you need several data elements about something, those are attributes (fields) about an entity.

Sort the entities into types: Events anything that happens about which we want to capture

information (transaction, meeting, call, appointment, order, sale, etc.) Agents people involved in those events Resources either assets (cash, inventory, etc) or anything else of

value (services, processes) that are involved in the events, and about which the organization wants to record information.

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ERD Modeling Approach

Connect up entities with appropriate relationships Determine the cardinality of the relationships

The cardinality question is One record of the first entity can be associated with how many records of the second entity at minimumand maximum?

In assigning cardinalities, use the normal guidelines, but remember: what determines the cardinalities are the business rules of the particular case!

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Database Design

In a relational database we are collecting attributes in tables.

Which attributes go in which tables and how are tables linked and queried?

2 basic approaches

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Database DesignApproach 1

Gather attributes from current business documents (invoices, master files, etc.)

Group into tables according to most likely dependencies, add keys

Use normalization rules to adjust table design to eliminate anomalies

Eliminate derived attributes

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Database DesignApproach 2

Use the Entity Relationship Diagram (REA version) to model data

Convert the ERD into schema (table design) and determine all attributes and keys

Check design against normalization rules Eliminate derived attributes

ENDReview of ERD Modeling and

Database Design

Database Accounting SystemsActg/IDS 475

das - database design (erd) .pdf

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